RPM Test; a tale of three twists, Chapter 2

[Larry Gibson]

RPM Test; a tale with three twists

Chapter 2; Test 1 [311291 of 2/1 alloy]

Yesterday broke clear with the promise of some warmth and little wind so I packed up the three rifles, the M43 PBL, the test ammo and the usual other necessary accoutrements for the range and set off the Tacoma Rifle and Revolver Club to conduct the first test. The primary goal of this test was to see if we could determine what causes the 311291 cast bullet to loose accuracy at a certain level. On arrival at TRRC I proceeded to set up. The benches there are very solid benchrest designed and made. It was about 46-48 degrees in the shade of the firing line but was into the 50s in the sunshine. Wind was coming out of 11 o’clock at 1-3 mph. The target distance was 103 yards. The testing was begun using the 10” twist rifle and then the 12” twist rifle and finally the 14” twist rifle. The barrels were cleaned between every two 5 shot groups with 2 foulers fired before testing was resumed. All data was collected via the M43 using pressure recording, muzzle screens and down range screens. Besides information on the rifle, load and test conditions the M43 provided data on the following information;

Data recorded for each shot;
• Velocity at the muzzle screens
• Proof variance of muzzle screens
• Time Of Flight between muzzle screens and down range screens (in front of 100 yard target)
• The down range velocity
• Proof variance of down range screens
• Ballistic Coefficient
• Peak average pressure (psi.m43)
• Area under the pressure curve
• Rise of pressure curve
• Actual pressure curve

Summary of shot data for recorded shots in the group;
• Average velocity at muzzle screens
• Average Proof variance of muzzle screens
• Average TOF
• Average down range velocity at down range screens
• Average proof variance of down range screens
• Average Ballistic Coefficient
• Average peak pressure
• Average area under the pressure curve
• Average rise of pressure curve
• Standard Deviation of each of the above data averages
• The high reading of each of the above data fields
• The low reading of each of the above data fields
• The Extreme Spread of each of the above data fields.

The M43 also provided the additional data on Standard Atmospheric Ballistics;
• Bullet path from muzzle to 250 yards based on data entered and the actual BC
• 10 mph wind deflection
• Computed muzzle velocity (fps)
• Energy (ft-lbs)
• Power factor
• Recoil of the rifle

The testing was uneventful except for one low shot that hit one of the down range screens….ooops! It knocked a chunk of the plastic off but didn’t actually hurt anything. As the groups enlarged I did have a few rounds that hit on the edge of the window and didn’t read. This cut some of the group data to 4 shots instead of 5 and one group to 3 shots of recorded data. The first test was with the 311291 cast of 2 parts WW to 1 part linotype. This gives an alloy that with the bullets air cooled the hardness of the bullets is similar to Lyman’s #2 alloy. That has long been a standard for cast bullets. As mentioned in Chapter 1, the cases for all three rifles were fire formed to the specific rifles and “match prepped” as such. The primers used are WLRs. Two powders were used. H4895, a medium burning powder, was used with a Dacron filler in 2 gr increments from 26 gr to 38 gr. This was expected, and did, to give velocities from 1700 fps or so up through 2500 fps. The second powder tested was H4831SC, a slow burning powder, loaded in 2 gr increments from 40 to 46 gr to give from 90 to 100% loading density. The only sorting done with the 311291 bullets were to inspect them for wrinkles, voids of non fillout. None were weighed for segregation by weight. The gas checks used were Hornady’s. They were pre-seated with the Lyman GC seater on a Lyman 450 with the .311 H die and then lubed in the .310 H die. The lube used was Javelina. At no time during the test was there any indication of leading or “lube failure”.

All told in Test 1 I fired 75 shots for record plus 10 foulers through each rifle for a total of 250 shots . After returning home it seemed a daunting task to sort through the data, measure groups and put it into some format that is easily presented on this forum. I could list all sorts of numbers in various manners but that would just get confusing. From the listed data the M43 provides on each shot plus the averages let me tell you I’ve got lots of numbers! I decided instead to put the pertinent data onto graph form. That is a “visual” way to present information and it gives valid comparisons which are easy to see and make comparisons from. It is easy enough to pull additional information of the graphs if you want it. However the little squares of the graph did not scan well so if you want some specific information don’t hesitate to ask. I couldn’t get the graph on this computer to work right so I resorted to graph paper and hand plotted them.

Without further ado we might as well get to the meat and potatoes of the test. Graph #1 is a comparison of velocity and pressure. There was considerable consternation from some forum members that pressures would not be “exact” between the rifles. I stated that, disregarding the fact that there is always variation of pressures, even with the same load in the same rifle; the pressures need not be the same in each rifle. In fact they were not. When we graph out the velocity/pressure of the same increasing loads out of different rifles what we expect to see is a linear relationship between them. The linear lines for each (red = 10” twist, blue = 12” twist, green = 14” twist) should run fairly parallel. This gives us a valid comparison of the time pressure curves of each rifle with the other rifles time pressure curves. That’s exactly what we see in graph #1. As the pressure increases the velocity increases pretty close for the 10 and 12” twist rifles but the 14” had some problems. We also see a slight divergence as velocity increases. This is expected as the 12 and 14” twist barrels were longer than the 10” twist barrel so velocity increased more as pressure was increased. Thus the comparison between the rifles is valid as the linear progressions are close to the same. Were one of them radically different then it would be obvious a comparison wasn’t valid. However there is a slight anomaly with the 14” twist. We could pontificate as to why and probably come up with numerous reasons, most of which would probably be wrong. So let’s what the data can tell us regarding that anomaly.

The answer to the velocity/pressure anomaly with the 14” twist is rather simple and is demonstrated in graph #2. The relationship between pressure and velocity is encompassed in internal ballistics so we merely need to look at that data showing the consistency of the loads, i.e. how consistent the powder burns. Consistency of a load (given a test string of several shots) is most often expressed in Extreme Spread of velocity and Standard Deviation of the combined averages of velocity. SD tells us what a load may do but ES tells us what that load did do. Since I am interested in what the load did do I compared the ES consistency of the loads with the pressure. In graph #2 the loads of the 10 and 12" twists all had ESs of 50 fps or less. That is pretty good consistency given the spread of the loads velocities of 1700 fps through 2500 fps. The 14” twist had some early problems with the powder burning efficiently. We see the ES for the 2nd and 3rd test loads was considerably higher than the same loads in the 10 and 12” twists. That accounts for the small anomaly in the pressure curve of the 14” twist on graph #1. The other, and perhaps more important, piece of information graph #1 gives us is the time pressure curve of the same loads in the different twists. Obviously the curves are pretty close together and linear. Thus the time pressure curve or acceleration is very close to the same for each rifle.

Next let us consider the question; if the time pressure curves are the same then any deformation to the bullet due to acceleration will be close to the same. Thus if the deformation to each bullet is the same at the same rate of acceleration then any change to the form of the bullet will result in a change to the Ballistic Coefficient. Following that then won’t any changes to the BC be the same for each twist since any deformation of the bullet should be the same? To find the answer to that question we merely compare the BCs of the 3 different twists as the velocity increases (hence the acceleration increases and deformation of the bullet increases). Graph #3 provides the comparison of the BCs vs the velocities of each load in each twist. Let us remember that the BC in this case is a measured BC from the actual flight of the bullets not a guestimated one from some chart. These actual BCs measured the bullets ability to fly through the air efficiently. The higher the BC the less deformed and more stabilized the bullet was. It is readily apparent that the BCs stayed pretty much the same for all three twists during acceleration at all velocities and pressures. It is interesting to note that the BCs of the bullets from the 10” twist retained the highest BC at the highest velocity (acceleration). This is just the opposite what it would be as believed by some on this forum. The BCs from the bullets from all three twists stayed very close together and linear across the wide spectrum of velocity (acceleration) from 1700 to 2500 fps which obviously shows the acceleration remained constant regardless of the twist of the barrel.

So this is what we now know now about the same loads in the 3 different twists; the time pressure curve is the same, the acceleration is the same and the BCs remain the same. Let’s now take a look at the results on target. After all what we are looking at in conducting this test is the accuracy at higher velocity and why that accuracy goes bad. Graph #4 shows us the group sizes vs pressure. Whoa there! Something is amiss….if the time pressure curves are the same, the acceleration the same and the BCs are the same; then if the groups get larger as we increase velocity shouldn’t the groups get larger by proportionally the same amount? [Note; by “proportional amount” is an amount to compare the accuracy of each twist to each other. The proportional amount of increase is found by dividing the increased group size by the smallest group with each rifle.] However, what we see is that the groups do not get proportionally larger as velocity increases. The inaccuracy of the 10” twist increases 5.38 while the inaccuracy of the 12” twist increases 3.14 and 14” twist increases 2.08. Hmmmmmm……pressure curve is the same, deformation of the bullet from acceleration is the same then why doesn’t inaccuracy increase the same? Especially since graph #4 shows the group size vs pressure. But wait…there’s more (sorry, just couldn’t resist!). Doesn’t every one say that it is pressure that destroys accuracy? We do see that accuracy with all three twists is decreasing with the increase of pressure. If pressure was the only reason for the decrease in inaccuracy then the inaccuracy should be proportional and it isn’t. We also see inaccuracy increases much more with the 10” twist than either the 12 or 14” twists. We also see the 12” twist’s inaccuracy to increase more rapidly than the 14”s inaccuracy. Again, if it was pressure that increased the inaccuracy then why doesn’t the inaccuracy of all three twists increase equally as the pressure increases? It seems there is something other than pressure adversely affecting accuracy and to a much greater extent.

Okay, let’s look at it one more way just to be fair. Graph #5 compares accuracy to velocity. Something wrong here again….that dreadful 10” twist is once again being more inaccurate by a greater proportional amount than either the 12 or 14” twists. How can this be? We know the acceleration is the same; the BCs are the same so the deformation of the bullet is the same yet the 10” twists inaccuracy is disproportional to the 12 and 14” twists. It should be the same amount of inaccuracy, right? The lines for each twist should be linear right? Yet the proportional inaccuracy are not the same between the twists nor are the lines linear. Have we missed something? Is there another game afoot? We’ve a good handle on the internal ballistics. We know about the terminal ballistics as the groups are self revealing. But have we really looked hard at the external ballistics (the bullets flight)? We know the bullets are stable, we know the BCs are getting smaller telling us there is some deformation from the acceleration. We know the 10” twist had the highest BC at the highest pressure and velocity so why isn’t it as accurate as the 12 and 14” twists?

Let us look at graph #6. It is a comparison of group sizes vs RPM. Note the very, very obvious adverse affect that the increasing RPM has on the accuracy of the 10” twist. That red line really climbs up there! Also note that area of RPM where the majority of accurate groups fall; it is in or below the RPM threshold. Also note that in or at the top end of the RPM threshold is where accuracy begins to deteriorate.

The tests with H4831SC seemed to be headed the same way but were inconclusive as top velocity was only 2287 fps with 100% loading density. The 10” twist velocity was 1928 fps through 2287 fps with groups running from 2.4” to 3.3”. RPM was 138,900 to 164,700. Conversely the 14” twist went from 1906 fps to 2265 fps. Groups ran .95” to 2.2”. RPM was 98,000 to 116,600. The highest peak pressure was 39,600 psi.M43. Thus I couldn’t get into a high enough pressure/RPM range with all three twists to make any comparison.

I am not going to conclude that there is an RPM threshold as the test is not complete. I shall wait until I conclude the test before giving a firm conclusion.

Chapter 3 will be to see how I can improve on and perhaps push the threshold with 311291 in all 3 twists. I have some cast of linotype (that’s pretty hard stuff). I have them weighed to a +/- ½ gr. I weighed them “dressed” for summer (that’s with just the GC on, not fully “dressed” with lube too). I plan on using Varget and RL15. Probably won’t get around to testing those until May.

Larry Gibson

To be continued:

[sundog]

It's turning into a doctoral thesis...

[felix]

Jolly good show, Larry! Thank you, and please continue the good work. A little overkill for this board, but that's OK too. But, it does remind me of my work days, a'la' Sundog's interpretation. ... felix

[carpetman]

Larry Gibson---I am impressed you finally got consistency correct.

[Larry Gibson]

Larry Gibson---I am impressed you finally got consistency correct.

Just goes to show I can learn new tricks...;-)

Larry Gibson

[Sailman]

Larry
Congratulatinons On your work and it's presentation.

Please continue with your research.

Sailman

[LeadThrower]

A great bit of prose, and fantastic display of data!
Kudos!

[Blammer]

Outstanding!

I suppose I'll be looking for a 1/14 twist now... :)

[Blammer]

I wonder if we could 'sticky' these some where?

[leftiye]

Larry, it is a fine piece of work! B.C. itself however does not necessarily capture the issue of deformation. Base deformations such as blowby- gas cutting might actually show up as an increase in B.C., as could some variations of nose slump. Nor does it obviate the issue of well formed, but out of balance still. We all know what deformed bases do to accuracy.

[Larry Gibson]

letiye

I think we can agree that the measurement called "BC" measures the efficiency with which a bullet flies through the air. The higher the BC the more efficient the bullet form; i.e. the bullet is balanced with the center of spin close to the center of gravity, stabilized and flying nose forward.
Since deformations caused by gas blow by and nose slump are unevenly distributed about the bullet they induce "out of balance". This means the bullet is not flying through the air efficiently; i.e. the bullet is out of balance, the center of spin is not close to the center of gravity, the bullet may have stability problems. Additionally an uneven base creates yaw and pitch which you correctly state “we all know what deformed bases do to accuracy”. All of these are factors that detract from a bullets efficient flight through the air decrease the BC of a bullet.

Could you please elucidate on how these deformations (slumped nose and uneven base) “might actually show up as an increase in B.C.” as I don't understand how they could?

Thank you for the compliment.

Larry Gibson

[leftiye]

Higher ballistic coefficients do result from other things than better balance (shape for instance). Though you are correct, I think, that out of balance should reflect in somewhat poorer flight characteristics, there are other factors than balance around the axis of weight as affected by rpm that produce loss of accuracy. The actual shapes producing the out of balance would be one. And this is often a result of deformation or flaws in casting that affect flight without resulting in velocity loss. Didn't your test show the 1 in 10 B.C.s getting better while the accuracy went south at high velocities?

They do not necessarily produce balance problems, only a change in shape which is not necessarily bad from an aerodynamic viewpoint. An uneven base may produce little or no imbalance, only a bullet thrown out of line with the intended path (also known as a flier) when the gasses act unevenly on it as it leaves the muzzle. At the same time ballistic stability, and coefficient may be unaffected. I'm not convinced that yawing, etc have to be in the picture, though often (or most of the time) they are.

A slumped nose could concieveably improve aerodynamics, (though not muy likely, and concentric slumping is probly an unusual event). Other than RPM, the slumped nose if not concentric, will induce the spiral flight path thang due to air resistance. While this kinda thing will possibly slow the boolit (though not necessarily), and refect in changed BC, it is not really an rpm phenomenon in terms of how it buggers up groups. I guess we'd have to call it a flight path or aerodynamic effect. The point being that while not to be expected often, things like this do happen. Further, they too can be so small in size as to be undetectable, just as the imbalances usually are.

Justa side thought, how does this apply to those who "shoot 'em anyway" anything thet comes out of the mold? A lot of those imperfections cannot be culled out with any method I know of, and especially at lower velocities are supposed to shoot as well as the carefully culled boolits.

[Larry Gibson]

leftiye

Excellent response, now I know where you are coming from and I agree. A good example is the out of round bullet produced by 2 groove '03 barrels. I also shoot a lot of my "culls". I shoot them as sighters and foulers and just for general shooting. You are right in that the ones with minor imperfections shoot quite well at lower velocities which coincide with the low end of the RPM threshold or under it. This is because the centrifugal force is not great enough at the lower velocity/RPM level to over come the rotational stability of the bullet. If you note in my explanations I said a lower BC could be the result of instability or deformation or both. Also we need to remember that as velocity increases with most cast bullets the BC will also decrease (RN and FN bullets). This to be expected. If we know what the rate of change is with a hard bullet (linotype for instance) and the same bullet of a softer alloy gives a higher rate of change then we know the softer bullets shape is getting deformed and the bullet is out of balance through accelleration. Good topic and good food for thought.

Larry Gibson

[leftiye]

Dang, I put my asbestos diaper on for nuthin'

[joeb33050]

Larry;
Do you have the numbers where you could send them to me? Excel maybe? I do better understanding the numbers.
Thanks;
joe b.

[Ricochet]

Asbestos diaper? You been eatin' Mexican?

[eka]

I just love it when you guys get into these deep technical discussions. I bring my wife in here and show her proof positive that other people are afflicted as bad or worse than me. :mrgreen:

Awesome show, keep it up. :drinks:

Keith

[44man]

I wonder how the average pressure, pressure rise, average area under the pressure, average rise under the pressure, actual pressure curve and peak pressure was measured? Is this from published data?

[runfiverun]

it would seem to me that if boolit deformation is causing the better b.c
that by switching to lino will bear that out.
or point in its direction.
hate to say it but the "better" boolit may not be

[Larry Gibson]

I wonder how the average pressure, pressure rise, average area under the pressure, average rise under the pressure, actual pressure curve and peak pressure was measured? Is this from published data?

44man

This is not from "published data". The average pressure, pressure rise, average area under the pressure, average rise under the pressure, actual pressure curve and peak pressure was measured by the M43. There is a strain gauge attached to the barrel over the chamber.

Attached photo shows it on the M98 Palma. It is firmly attached and to remove it would be to destroy it by scraping it off. On the Palma rifle and a couple others I have it mounted on top as the gauge showing doesn't matter. On rifle I don’t want the gauge to show it is attached on the bottom of the barrel and hidden by the stock. The wires to the gauge are readily attached and unattached on those rifles.

Also attached is the print out of the data recorded for the 32 gr load of H4895 as tested in the M70. I compute and write the RPM (rounded to nearest 100 RPM) in the “Summery Column”. I use the average velocity as measured by the muzzle screens. I suppose I could use the computed muzzle velocity but since I am consistent and round off the few fps difference doesn’t matter. I also write the size of the group under the actual pressure curve. In my record book I normal cut out the group from the target and paste it here for record. In this case I am keeping all the targets with the records of this test in a separate hard copy binder.

Note on the actual pressure curve the little dog leg as the pressure begins to rise; this is consistent with all cast bullet loads tested so far. It is not consistent and most often not present on jacketed bullet tests. I believe this is showing the entry of the bullet into the rifling. Once the cast bullet is engraved the pressure rise slows a bit then continues its rise. I will query Dr. Oehler on this.

Larry Gibson

[Larry Gibson]

Larry;
Do you have the numbers where you could send them to me? Excel maybe? I do better understanding the numbers.
Thanks;
joe b.

Joe

Sorry, I do not have the numbers collated on a spread sheet. Look at the Oehler test print out in the response to 44man and you will get an idea of the volume of numbers and the job that would be to spread sheet them. I have 22 such record print outs for the first test alone. I could scan them all or copy them and mail them (easiest).

Larry Gibson

[Larry Gibson]

it would seem to me that if boolit deformation is causing the better b.c
that by switching to lino will bear that out.
or point in its direction.
hate to say it but the "better" boolit may not be

Except with perhaps a rare occasion that leftiye and I discussed the BC of a deformed bullet will be worse. We will see how the linotype 311291s fare in Chapter 3. Knowing the BCs of RN & FN bullets decrease with the increase of velocity it will be interesting to note the difference in that increase between the two alloys. If perchance the BC change is close to the same then it is telling the #2 alloy held up very well with little deformation. Of course it could be completely different and right now I don't know. We shall see.

Apparently we lost part of your message. What do you mean with; "hate to say it but the "better" boolit may not be"?

Larry Gibson

[Larry Gibson]

I just love it when you guys get into these deep technical discussions. I bring my wife in here and show her proof positive that other people are afflicted as bad or worse than me. :mrgreen:

Awesome show, keep it up. :drinks:

Keith

Keith

If you've got the "affliction" leap on into the discussion:-)

Larry Gibson

[felix]

Larry, use a side test with 4227/2400 at about 23-25 grains with either boolit and to see if the little wiggles go away, or strongly diminish, during the ignition stage. That will tell you the story without calling Oehler. ... felix

[Larry Gibson]

Larry, use a side test with 4227/2400 at about 23-25 grains with either boolit and to see if the little wiggles go away, or strongly diminish, during the ignition stage. That will tell you the story without calling Oehler. ... felix

felix

Good idea, I had planned on using those powders also at the end of this test. Someone else had requested a test with "faster powders".

Larry Gibson

[runfiverun]

larry
what i meant was the harder boolit may not show this anomaly
to "set back" and show the better or as good as bc.
i have run into the [ problem ] of going to a harder boolit did not really gain
me more. accuracy or what have you at least not enough to justify the extra cost.

[Larry Gibson]

larry
what i meant was the harder boolit may not show this anomaly
to "set back" and show the better or as good as bc.
i have run into the [ problem ] of going to a harder boolit did not really gain
me more. accuracy or what have you at least not enough to justify the extra cost.

That has been my general experience with bore riders in the quicker twists of 10" and faster. This is why I mostly just shoot bore riders cast of ACWWs at 1800-1900 fps in the 9 1/2-10" twist barrels. However with slower powders I have pushed the RPM threshold in a couple of those but not very much. I've gotten away with some pretty decent accuracy in the 2000+ fps range years back with the two Lyman Lovern bullets cast in linotype in 8x57 which is pushing the RPM threshold. In 12-14" twist barrels of several calibers I have run some pretty decent accuracy at higher velocity with the harder bullets. However all have really been within the RPM threshold. Also I've not pushed a good bore rider like 311291 in a 14" twist before when cast hard. Will be interesting to see if it fares any better than the #2 type alloy.

Larry Gibson

[runfiverun]

i just read my own post
i need to use ing and commas and stuff.
my elementary school teacher would be proud?

[Bass Ackward]

Larry,

I think you draw some interesting conclusions about pressure curve with the twist rates that are not correct. Listen to my grandson.

Watched my grandson with his pedal car in the driveway. He was sitting still and I cut the wheels hard to the right and asked him to start out. He said grampa, you need to straighten the wheels out some and then turn if you need to otherwise it's too hard to pedal.

Load from 11 to 15 grains of Red Dot. That should max out between 1700 and 1800 fps which is the ideal RPM range. See if you get different accuracy from the three twists even in the ideal RPM zone. If the accuracy is different in the ideal zone, then the only variable has to be pressure. Please post those group sizes.

[runfiverun]

bass
straightening the wheels would be like straightening the
twist in a bbl wouldn't it?

[leftiye]

Dern smart kid!

[Larry Gibson]

Larry,

I think you draw some interesting conclusions about pressure curve with the twist rates that are not correct. Listen to my grandson.

Watched my grandson with his pedal car in the driveway. He was sitting still and I cut the wheels hard to the right and asked him to start out. He said grampa, you need to straighten the wheels out some and then turn if you need to otherwise it's too hard to pedal.

Load from 11 to 15 grains of Red Dot. That should max out between 1700 and 1800 fps which is the ideal RPM range. See if you get different accuracy from the three twists even in the ideal RPM zone. If the accuracy is different in the ideal zone, then the only variable has to be pressure. Please post those group sizes.

Bass

With all due respect to your grandson; you just aren't getting it. I don't "draw interesting conclusions". The facts on the pressure curves are there. Perhaps you failed to look at the graph on group size vs pressure and the graph on group size vs velocity. You're the one who disagrees with RPM threshold with regards to high velocity loads. With the facts clearly beginning to demonstrate there is a RPM threshold with regards to high velocity, you now want to revert back to medium velocity? Give us a break, at least try to keep your story straight.

As to your test with Red Dot; define "different accuracy". The test has already demonstrated that pressure was not what caused the proportionally greater group sizes. It was the increased RPM of the faster twist that caused the proportionally larger groups.

Also when have we ever said 1700-1800 fps was the "ideal RPM range"? Since RPM is a function of twist and velocity (or have you forgotten?) at 1700-1800 fps; the 10" twist will be doing 122,500 - 129,700 RPM, the 12" twist will be doing 102,000 - 108,00 and the 14" twist will be doing 87,500 - 92,600 RPM. Which one of those 3 different RPM levels do you consider "ideal"? Since the RPM is in fact varied, how is pressure then the “only variable? It isn’t, is it.

Further more, since the RPM threshold (the topic of this test and this discussion, remember?) is 125,000 - 140,000 RPM and involves inaccuracy induced when RPM overcomes the rotational stability of the bullet in or above that threshold I just don't see where your test is relevant.

Larry Gibson

[Larry Gibson]

bass
straightening the wheels would be like straightening the
twist in a bbl wouldn't it?

It doesn't work out like Bass seems to think it does. Unfortuneately for many, many years others have believed that pressure was the culprit also. You will read that over and over again in numerous writing and publications. All of them ignore the effects of RPM. Pressure is certainly partially to blame as it is what creates the defects in the bullets (given a quality cast bullet) during accelleration. However, it is RPM that adversely affects the bullet during flight creating the inaccuracy. If it was just pressure then explain how it is that when the pressure is the same in the 10" twist and the 14" twist the 10" twist is still proportionately more inaccurate? The answer is simple, RPM.

Bass just doesn't see that as apparently do numerous other people who've believed for years that it was pressure.

Pressure the same, accuracy is not the same; 10" twist has worse accuracy than 14" twist.......hmmmmm.........RPM higher in 10" twist than 14" twist........accuracy worse in 10" twist.........pressure is the same.....hmmmmmm. Not to hard to understand.

Larry Gibson

[Bass Ackward]

Larry,

I try to consider everything. I suppose RPM forces in the bore explains why lube sizing of bullets lets go worse in colder weather But in the warm it does OK with pressure being constant. Why rifling height makes a difference too. But pressure is still there as well as RPMs.

My tests with defacing bullets showed the worst results when the base was disturbed. And we have history on crown research too. I have shot plenty of good bullets at low RPMs badly and quite a few good bullets at high RPM well. So RPMs can't explain everything.

If RPMs explains HV, it has to apply in some regard at low? RPMs is used as an excuse to explain failure when the security of cast comfort levels are surpassed.

What ties pressure and RPMs together is hardness as it defeats both. And why we hear match hardness to the velocity of interest. Not to the pressure of interest, not the RPMs of interest, but velocity. So maybe both are at work.

But think my granson is wrong huh? Take your car and cut your wheels in the angle of a 10 twist and slowly step on the gas from a dead stop. Feel how much more gas it takes to get your car moving than with the wheels straighter. Everything has an effect, don't blind yourself to it. If this could be defined simply, then we would have answers now.

[felix]

The base of the boolit must be DYNAMICALLY the same at the muzzle during the entire duration of each boolit exit. Otherwise, we are really sucking wind on this RPM endeavor. The duration is defined as the time it takes when the pressure between the boolit base and the barrel becomes zero. "Dynamically the same" means the base remains perfectly round for all pressures/twists without regard to base expansion or contraction at exit. This has to explain why boat tails and flat based projectiles can shoot identically out of the same gun, but in most guns they do not. Obturation style is paramount. ... felix

[sundog]

Boolits don't have steering wheels, in and of themselves, if they are good boolits to begin with. The steering wheels are 'induced' by such things as poor alignment, poor throat to boolit fit, poor land/groove consistency, poor boolit exit or poor crown, etc., basically all those things we've been discussing.

So, the more twist you put on the boolit (one factor that can affect it's 'steering wheels') the more chance you have of inducing failure - inability to get started.

Don't forget, the barrel is a swaging device. If the boolit is not swaged perfectly, then you get what you get, which is less than perfect performance.

I'm not taking any sides on any of this, just thinking out loud. I know the things that work for me, so anything I can learn new from y'all is just like eating chocolate pudding (which to me is 'pretty good stuff, Maynard!')

[felix]

Yeah, it's tough to make RPM a true independent variable when considering this mess of variables which seem to depend on each other so strongly in our discussions. ... felix

[Larry Gibson]

Bass Ackward

Okay bass, lets go through this one more time.

I try to consider everything. I suppose RPM forces in the bore explains why lube sizing of bullets lets go worse in colder weather But in the warm it does OK with pressure being constant. Why rifling height makes a difference too. But pressure is still there as well as RPMs.

I don't think you are trying to consider everything. I think you are searching, sometimes even grasping, for a something to validate something you (your not alone as there are many others) have believed for many years. I believed it for many years also. But the more I looked at it the less pressure answered the question. How many times have we heard or seen it written; “I load 311359 in my .30 carbine to 40,000 psi and it shoots great. But when I load it to the same pressure in my 30-06 it shoots terribly." Or as published in the current Lyman manual; "Load Lyman's 311291 in a 30-30 case at about 40,000 psi. In a good rifle it will shoot alongside jacketed ammo of the best quality, if properly made and loaded. Now load it to 40,000 psi in a .300 Magnum. The only thing it will shoot along side of is a blunderbuss-if you're lucky." Everyone wants to say it is pressure but yet they constantly give examples where it is not pressure. None of those who say it is pressure even consider that it might be something else. That is because everyone else says it is pressure so it must be. But it is not pressure. I did not dream this idea of an RPM threshold up myself. There have been several others over the years who've said the same thing.

Have you ever consider that it is the cold making the lube harder as the reason it "let's go"? Probably not. I and numerous others conducted tests back in the '70s on that very subject. The lube residue in the bore gets harder in cold weather. Ever notice in cold weather with a fouled cold bore the first 2-3 shots are the flyers? When the barrel has warmed up the rest of the string shoots to group.

Lube failing and the height of rifling all have effects in the bore. Once again the RPM effects the bullet outside the bore.

My tests with defacing bullets showed the worst results when the base was disturbed. And we have history on crown research too. I have shot plenty of good bullets at low RPMs badly and quite a few good bullets at high RPM well. So RPMs can't explain everything.

If RPMs explains HV, it has to apply in some regard at low? RPMs is used as an excuse to explain failure when the security of cast comfort levels are surpassed.

[B]during flightand inaccuracy results.

The effects of RPM do apply at lower pressures. Cast the bullet of just soft lead and how fast can we shoot it before accuracy fails? How fast can we shoot PB bullets before accuracy fails? The answer is increased pressure has caused defects in the bullets during acceleration at a lower level and RPM during flight causes the then unbalanced bullet to be inaccurate. How many times have I told you that all bullets are imbalanced even jacketed bullets? When the center of spin does not coincide with the center of form or the center of gravity the bullet is unbalanced. RPM will adversely affect the accurate flight of every unbalanced bullet. How much that affect is depends on the amount of imbalance. That is why we shoot bullets into groups instead of one hole.

"RPMs is used as an excuse to explain failure when the security of cast comfort levels are surpassed." Let us substitute "pressure" for "RPM" and we have your excuse. However I am proving the effect of RPMs so it is not an excuse. Also, as you have failed to notice, I also am proving the adverse effects pressure has on the bullet during acceleration. /B]
What ties pressure and RPMs together is hardness as it defeats both. And why we hear match hardness to the velocity of interest. Not to the pressure of interest, not the RPMs of interest, but velocity. So maybe both are at work.

"So maybe both are at work." Perhaps you are getting the idea. Cast a harder bullet of better design that resists deformation during acceleration and you can push the RPM threshold for that bullet up to a much higher velocity. Your work with the LBT bullet is good proof of that. Just increasing the hardness of a regular cast bullet also allows you to push the RPM threshold but not nearly as much.

But think my granson is wrong huh? Take your car and cut your wheels in the angle of a 10 twist and slowly step on the gas from a dead stop. Feel how much more gas it takes to get your car moving than with the wheels straighter. Everything has an effect, don't blind yourself to it. If this could be defined simply, then we would have answers now.


Never said your grandson was wrong, it was he I was giving "due credit" to. If you are inferring that pressure with a given load is higher in quicker twist barrels then you are correct. The M43s measurements clearly show that. However the comparison of groups was with equal pressures in all three barrels. That comparison clearly shows the proportional increase in group size is larger with the faster twist.

I do not blind myself. It is you who have the blinders on. You actually see the relationship that pressure has during acceleration on the integrity of a cast bullet. You do understand how that acceleration from pressure causes defects in the balance of the bullet. What you fail to see is that it is the centrifugal force of RPM that adversely affects the bullets flight and causes the inaccuracy. If you would quit grasping at straws to prove it is pressure when there is ample evidence it is not pressure then you would understand the relationship of the two. You would understand the cause and effect of each and have a better understanding of the cast bullet in flight. Take the blinders off Bass.

Larry Gibson

[Larry Gibson]

sundog

Quite correct; it is all of those things that cuase the defects in the balance of the bullet while inside the barrel. It is the RPM during flight outside the barrel that causes the inaccuracy. The greater the defects, the higher the RPM the greater the inaccuracy.

Larry Gibson

[Larry Gibson]

Bass

One other reminder; you've not answered the question, "As to your test with Red Dot; define "different accuracy"." with regards to your test with Red Dot. Are you now not wanting to proceed in that direction?

Larry Gibson

[sundog]

Larry, yeah, kinda knew that all along. The problem is reducing all those detrimental things to near zero. We can heap environmental conditions on top of all that, too, as in temp, humidity, pressure, wind, sun angle, brightness, etc. Damage that occurs after ignition and before exit is amplified by increased rpm. The less the damage, the less the amplification of error. Changing any condition will change the threshold.

But, unless a load is faithfully repeatable across a range of conditions, what use is it?

Patiently waiting for further testing....

[Larry Gibson]

Concur...Changes we make does change the threshold but I've noticed for some years that with regular cast bullets in rifles it doesn't change that much. If accuracy strats going bad at say 128,000 RPM and we harden the bullet so accuracy stays good through 138,000 RPM we have accomplished something but are still within the threshold. I've found over the years that it is difficult to get consistant good accuracy above the threshold, i.e. above 140,000 RPM. I never had the means to test it that accurately before as I do now. We will see if my suspicians are correct.

Larry Gibson

[runfiverun]

hmmmm.
1st the lube thing i have noticed that i use a heater to make my lube flow when
sizing, it also takes a few shots to warm the bbl and then accuracy occurs.

2nd i have always tried to match my pressures to my hardness
and have tried to tell others to do the same thing , if you are not pushing hard enough
or too hard.?

3rd as far as twist rate affecting pressure? i do know it takes more energy
to spin a bullet, and the faster you have to spin it, the more eenergy it takes
which will lower your velocity,
this may have something to do with that obturation thing and also the take care
of the boolit and it will show up on the other end.

some obsrevations

i also have proven to myself that acww will not go 1700 fps with out poor accuracy
and bed leadind no matter how much lube you use, or what pressure you do it with.

[leftiye]

sundog

Quite correct; it is all of those things that cuase the defects in the balance of the bullet while inside the barrel. It is the RPM during flight outside the barrel that causes the inaccuracy. The greater the defects, the higher the RPM the greater the inaccuracy.

Larry Gibson

Larry, Correction: It is the RPM [B] during flight outside the barrel that causes SOME OF THE (or adds to the, or aggravates the) inaccuracy. IMHO. Without rotational effects there will still be inaccuracy due to other factors. Since one cannot shoot a boolit without rotating it and get accurate results, these may be inseparable, but the other factors do still exist, and they still do cause inaccuracy. TomAYto, tomAHto.

[Larry Gibson]

Leftiye, correction: there are three types of ballistics; internal, external and terminal. Were all three the same there would be only “ballistics”. They are not the same and we must realize this. What happens inside the barrel (internal ballistics) to the bullet is not what happens out side the barrel (external Ballistics) to the bullet. What happens inside the barrel during acceleration or from a poor casting is what the RPM works on out side the barrel. The two what happens are different. One is not related to the other. The centrifugal effect of the RPM will be there whether or not the bullet is unbalanced. The unbalancing happens in the barrel, the inaccuracy happens out side the barrel when those imbalances are acted upon by the RPMs centrifugal force. No imbalance then the RPM does not act on it but the centrifugal force of the RPM is still there. Not realated but simple a cause and effect.

It is apples and oranges, not ; “TomAYto, tomAHto”

Some also are arguing that the different twists mean different pressure. Well duh okay, maybe a little but how much? Not very much really. There is ample evidence that once a bullet has gone one bearing length there is no longer any increased pressure required to keep in rotating. This has to do with Newton’s law about once in motion a body tends to stay in motion. That pertains to rotating bodies also.

Additionally some seem to think that since a bullet out of a 10” twist at 2000 fps is doing 144,000 RPM that as soon as the bullet enters the barrel it is doing that amount of RPM and therefore the centrifugal force must be the same "in the barrel". They equate this with some greater amount of pressure. Such is not true. The bullet goes from 0 to 2000 fps within the barrel so the RPM is increasing as the bullet travels down the barrel. The RPM goes from no RPM, 0 to 144,000 RPM as the bullet leaves the barrel. So we see that within the first half of the bullets travel within the barrel which happens to be where the pressure is the highest the RPM is actually quite low. The RPM of a bullet in this case at mid barrel is only 72,000 rpm give or take when the pressure is decreasing. The time pressure curves of the 10” twist are almost the same as that with the 12 and 14” twist barrels. If there were a much greater pressure difference the it would have been measured. It was not.

Larry Gibson

[felix]

Well, Larry, if the boolit is still accelerating, then the RPM is accelerating, on track, hopefully! Both take force to do so via F=MA, eh? Don't forget to consider the torque on the tail of the boolit as the forefront of the bearing surface leaves the muzzle! That difference in torque is an induced imbalance, as you know. A good-based, and tough-bodied, boolit should not see that as a fault, provided the twist is within range for the INERNALS of the boolit. ... felix

[Larry Gibson]

felix

"Don't forget to consider the torque on the tail of the boolit as the forefront of the bearing surface leaves the muzzle!"

I believe that is a "Bassism" that is still to be proven. I have recovered and inspected many, many bullets from down range as have many others and they make exactly the same observation I do. None indicate any additional signs of applied pressure to one side of the groove where this additional pressure, if it exists, would have to have exerted it self.

Kindly show me one single bullet that exhibits signs of pressure on one side of the groove where this pressure is applied.

Given that the "boolit is still accelerating" when exiting the barrel then since the front of the bullet is ahead of the rear of the bullet then it is theoretically rotating faster, right? Then is the rear of the bullet is trying to catch up with the front of the bullet in RPM, correct? So what happens to the middle of the bullet?

Now if we really want to believe this "Bassism" and think that bullets twist from the torque because the back of the bullet is rotating slower than the front of the bullet and is "catching up" after the front of the bullet exits the barrel then you're way beyond me. That falls right in there with those who want to believe that bullets go faster when exiting the barrel because of the release of pressure. I do not believe either one in the least bit.

Larry Gibson

[Larry Gibson]

leftiye

One other thing to remember; if there wasn't any centrifugal force from RPM an unbalanced bullet would fly as straight as a balanced bullet. As mentioned, the ballanced bullet is not affected by RPMs centifugal force because there is nothing for the centrifugal force to act upon. However, the centrifugal force is still there. It is the centrifugal force of the RPM that acts upon the imbalancing defects of the bullet to cause yaw, pitch and wobble. It is not the imbalances that cause yaw, pitch and wobble in bullets. Yaw, pitch and wobble are caused by RPM.

Larry Gibson

[leftiye]

Yes Larry there are any number of types of ballistics, oh well. Changing the terminology is irrelevant. These thangs all contribute to accuracy or the failure thereof. Isn't it interesting how every one in this discussion can be right? Isn't it interesting how we all agree on everything and yet still find substance for argument?

The issue to me is factors that contribute to failing accuracy, I don't care if they are in the ctg case, the leade , in the barrel, at the boolit's exit from the barrel, in flight, or in your grandma's purse. RPMs are just ONE OF THE MANY factors, even during flight. If you were to say "I want to study the effects of speed of rotation of the boolit as it affects accuracy, I would have no problem with that. The answer would be, the faster it revolves, the more effect it has. EOS

Unbalanced boolit versus balanced in the absence of centrifugal force - By this are you stipulating to boolits that fly straight without being revolved? If so they all would be accurate or inaccurate depending on all of the other factors except rpm/centrifugal force, ie. if they were accurate or not as the other factors determined. Yep, there are other thangs goin' on! They would NOT be accurate simply because centrifugal forse were negated.

[Larry Gibson]

leftiye

I'm not sure it's an argument (is that arguing?) but I rather consider it a discussion. We are in complete agreement. However as Bass has pointed out correctly; we must separate the various cause of inaccuracy and test each one separately. Otherwise we do not really know what the cause of the inaccuracy is. Unless we truly understand each cause of inaccuracy seperately we won't be able to adequately deal with it in its relationship to other causes. To pick on Bass again; he has adequately dealt with several of the major causes of inaccuracies with cast bullet using the 154 gr LBT bullet. Truly understanding what can be done by dealing with and understanding each of the causes will help us all achieve better accuracy. If we understand how harder alloys can better with stand acceleration, how we can use different powders to alter the time pressure curve, how different designs of cast bullets resist deformation under acceleration better, how to better fit the bullet to the leade and sizing it correctly and numerous other things then we can tie them together to produce a more balanced bullet. That bullet when fired at high velocity and subsequent high RPM will then be more accurate.

The other and perhaps more beneficial aspect to understanding how the RPM adversely affects the cast bullets flight comes when we are going to buy or build a rifle that we want good cast bullet accuracy in. If we want hunting cast bullets at 2200 -2400 fps then we know to get a 12” twist .308 instead of a 10” twist .308. We know that if rebarreling we should get the 12” twist or more probably a 13 or 14” twist barrel for best cast bullet accuracy at higher velocity. Understanding RPM and its affects we also know what cartridges best serve using a slower burning powder at close to 100% capacity to achieve the velocity level we want. Thus we see there are many other benefits to understanding the individual aspects of all the elements of accuracy of a cast bullet.

Larry Gibson

[leftiye]

Larry, Think philosophy. Arguement is a good word! I thought that people formulated arguements in the course of discussions. "Apology" is the presentation of an arguement in favor of a position. It's like the difference between gross frosting on a boolit, and the frosting that helps fillout. There are polite arguments, and there are heated arguments, and there are out of control arguents. And, yes, the more this happens, the more I suspect that we may actually agree. (I wasn't angry, I can't think that well if I am!)

[floodgate]

Larry:

"Some also are arguing that the different twists mean different pressure. Well duh okay, maybe a little but how much? Not very much really. There is ample evidence that once a bullet has gone one bearing length there is no longer any increased pressure required to keep in rotating. This has to do with Newton’s law about once in motion a body tends to stay in motion. That pertains to rotating bodies also."

As a retired (retarded?) physic ist, I've got to support Felix' comment on the above. So long as the bullet is accelerating in the bore, the RPM's are also increasing, and the Newtonian inertial reaction HAS to require increased pressure. Back in the early BP days, there was a lot of back and forth between proponents low- and high-twist rifling (back then, pre-Greenhill, they did not think of twist in inches per turn, but in turns - or fractions of turns - per barrel-length, since, all other things being equal, longer barrels, with correspondingly increased charges, gave higher velocities). The Baker rifles of 1803 or so traded twist (as I recall, 1/2 turn in the barrel) for speed in loading and decreased fouling: accepting the well-established loss in accuracy with the slow twist, they still far out-performed the muskets of the era.

But, none of the foregoing takes anything away from your EXTERIOR BALLISTCS study, so CARRY ON! - and keep us posted.

floodgate

[waksupi]

A most interesting thread.
Considering more pressure with a faster twist. Push a bowling ball up inclines, set at 10, 45, and 60 degrees. As the incline gets greater, more effort is used to move the object the same distance. Rifleing is an incline, and the principle should be the same.

[sundog]

Actually Ric, think of it as a screw as opposed to an incline. The more you got, the more screwed you are...

[Larry Gibson]

Leftiye

Very well put, outstanding actually. Thanks.

Larry Gibson

[Larry Gibson]

floodgate

Appreciate the support, thanks.

However regards the "Newtonian inertial reaction"; some would argue once the bullet has started to spin the inertia is very little if any as the bullet now has inertia in the direction of spin. Further retardation of that inertia as the RPM increase is little if any. As I stated many have recovered bullets down range but none have found evidence of additional pressure. The time pressure curve gives a clear picture of the engraving of the bullet into the rifling. The pressure rises and then lets off a little and then picks up again. Look at the time pressure curves on the Oehler printout I posted for 44man (I believe it is on the 1st page of this thread). Every single cast bullet rifle load shows this initial pressure let off after the bullet enters the barrel. The pressure curves show a more pronounced let off in the 12 and 14” twist barrels. This shows that the pressure backs off when the bullet starts spinning in the very first part of the barrel. There is nothing in the time pressure curves to indicate a greater pressure was required in the 10” twist to keep the bullet moving. There is an indication that a greater pressure was required to initially push the bullet into the barrel on the 10” twist but after that the pressure curves are essentially the same. I am open on this issue, my point is I've found no evidence of increased effort to move the bullet down the barrel in quicker twists. To the contrary I've evidence that supports the opposite. Like I said I'm still open on this one though.

Larry Gibson

[Larry Gibson]

waksupi

I agree, in theory it should be the same but from what I and others have found perhaps it's not the same.

Larry Gibson

[Bass Ackward]

bass
straightening the wheels would be like straightening the
twist in a bbl wouldn't it?


Works that way for everything else, so that's my theory.

[Bass Ackward]

Bass

One other reminder; you've not answered the question, "As to your test with Red Dot; define "different accuracy"." with regards to your test with Red Dot. Are you now not wanting to proceed in that direction?

Quite correct; it is all of those things that cuase the defects in the balance of the bullet while inside the barrel. It is the RPM during flight outside the barrel that causes the inaccuracy. The greater the defects, the higher the RPM the greater the inaccuracy.


Larry Gibson


Larry,

Forget the Red Dot. I'll not go into it. All it was going to show was that a poorly launched projectile was a poorly launched projectile no matter what the RPMs. But I would like an answer from you.

But again I am confused. I can take a 45 caliber rifle bullet at 57,600 RPM and make it shoot 18 inch groups in the cold. I can take the same mix in a 30 caliber and spin it at 180,000 and have it shoot 5" below 50 degrees. Which bullet do you think got more damaged, unbalanced, deformed? And it still shot better at 3 times the RPM. Both guns are MOA producers with no mechanical defects.

Bear in mind that this same bullet is stabilized at 1300 fps running 46,800 RPMs. Rpms are linear. Why then isn't accuracy linear if there are no other forces involved?

[w30wcf]

Bass Akward,
Hmmmm...... Wow! I have shot plenty of .45-70 bullets but never did I have anything approaching an 18" group. Was the sectional density / bullet fit to the barrel / bullet alloy similar to the recipe in your .30 cal.? I've pushed a softer 420 gr. 16/1lead/tin bullet to 1,850 f.p.s. (66,000 rpm) and got 4" groups @ 100 yards even with a bit of flinch. For me, a .45-70 is a bit harder to control with heavy recoiling loads than the .30 cal's.

Larry,
Great work! I will be interested to see how the harder Lino bullets do in your tests since the quicker twist at higher velocities would need a harder bullet for its best work.

You have come a long way since the "Old Gentleman" taught a 15 year old youngster how to reload .30-30 cartridges with a Lee Loader and 3118 cast bullets.:-D

w30wcf

[Larry Gibson]

Bass

As to the Red Dot test; the following also applies to it. If you remember the RPM threshold applies to otherwise accurate cast bullet rifles loads using medium and slow burning that are pushing higher RPM because of twist rate and velocity. We "can make" bullets/loads to be inaccurate, particularly with fast powders. By causing a lot of deformation and unbalancing through rapid acceleration the bullets, at the low twist rate of a 45 cal barrel, never attain complete rotational stability before the centrifugal force of the RPM overcame it. This occurs even at low RPM as you discovered.

RPM are only linear given the same twist with increasing or decreasing velocity. However, centrifugal force also increases as the RPMs increase. I'm not sure but perhaps the increased centrifugal force is not linear as the RPM increases (anyone know? I don’t have time to research it today.). I expect it is not as accuracy is not linear even with the same twist, i. e. the greater the RPM the inaccuracy is proportionally greater.

We do know that proportional accuracy is not linear with the same twist or when compared to other twists. Not only do my tests adequately proved that but I’m sure you and many others have also observed it in your own tests. I thoroughly expect the additional comparison tests of the 3 twists will show the same nonlinear inaccuracy.

Larry Gibson

[Larry Gibson]

w30wcf

I guess I have. I hope the "Old Gentleman" (God bless him) approves. He started me off on a wonderful adventure. Thanks for the support.

Larry Gibson

[Bass Ackward]

Larry,

According to the RPM theory, If bullet balance is the same, then accuracy would improve with lower RPMs correct?

Take one HV load in any one of those twist rate barrels and cut 12" off the barrel.

Acceleration should be the same, bullet deformation should be the same, velocity will drop so RPMs will drop. Therefore, the accuracy of the load should improve with every inch you cut off the barrel?

That removes all the variables except muzzle pressures as it will increase. It answers the question in a nut shell with no way to dispute it. If accuracy gets worse, it's pressure. If accuracy improves, it's RPMs.

[Larry Gibson]

Bass

"According to the RPM theory, If bullet balance is the same, then accuracy would improve with lower RPMs correct?"

The RPM threshold is in reference to the use of cast rifle bullets using medium and slow burning powder when we try to push them to higher velocity. It is that area of RPM (generally 125,000 to 140,000 RPM) where the centrigugal force overcomes the rotational stability and accuracy worsens. The accuracy gets worse than it was in or below the RPM threshold. If you've got good loads with well cast bullets you will have best accuracy in or below the RPM threshold. If you have poor loads that are relative inaccurate they will still be more accurate in or below the RPM threshold. It is a matter of proportional accuracy compared in and to itself.

However if the bullets are balanced the same and the loads are equal, within reasonable pressures and are consistant in ignition then the accuracy will probably be equal up to and into the RPM threshold, maybe even a little beyond. Remeber that it appears the centrifugal force is not linear, it gets stronger at higher RPM. Thus at the higher RPM, above the threshold, the accuracy will get still worse as the centrifugal force is greater. Maybe not by much depending on the extent of the imbalances in the bullets equal though they may be.

"Take one HV load in any one of those twist rate barrels and cut 12" off the barrel.

Acceleration should be the same, bullet deformation should be the same, velocity will drop so RPMs will drop. Therefore, the accuracy of the load should improve with every inch you cut off the barrel?

That removes all the variables except muzzle pressures as it will increase. It answers the question in a nut shell with no way to dispute it. If accuracy gets worse, it's pressure. If accuracy improves, it's RPMs."

That is a good assumption but it contains several caveats (those be variables BTW); it is correct only until the velocity/RPM comes back down to the level where that load produces the best accuracy in or below the RPM threshold. Also accelleration is not the same as you're removing barrel length which also shortens accelleration (that's why the velocity is less). Thus the bullet may have sustained less deformation during the lessoned acceleration. That induces several variables into your test and skews the basic premiss of this line of thinking. There are in fact variables.

You are grasping at straws again with to much postulation. It is easy to theorize what the results of an experiment may be. There is only one way to know whether you are right or wrong and what the results of an experiment are; that is to actually conduct the experiment. Since it is your theory and you want to cut barrels I'll defer the conduct of this experiment to you.

My tests are already confirming the existance of the RPM threshold and the effect increased RPM has on cast bullets. I "theorize" that further testing will confirm those facts. However I do not state that theory as fact yet becuase I have not completed the tests. Perhaps you shouldn't state your "theories" as facts until you have completed tests, leaves room for less embarassment. Want to borrow my hacksaw;-)

Larry Gibson

[joeb33050]

Larry,

According to the RPM theory, If bullet balance is the same, then accuracy would improve with lower RPMs correct?

Take one HV load in any one of those twist rate barrels and cut 12" off the barrel.

Acceleration should be the same, bullet deformation should be the same, velocity will drop so RPMs will drop. Therefore, the accuracy of the load should improve with every inch you cut off the barrel?

That removes all the variables except muzzle pressures as it will increase. It answers the question in a nut shell with no way to dispute it. If accuracy gets worse, it's pressure. If accuracy improves, it's RPMs.

If accuracy improves after you cut the barrel off, maybe the crown is better. Or maybe you cut off the accuracy-diminishing piece of the barrel. Or maybe the rifle/load likes lower velocities.
If accuracy gets worse after you cut off the barrel, maybe the crown is NFG. Or the rifle/load likes a slightly higher velocity. Or you're having a bad day.

As the exponent of the infinite-number-of-variables-so-we-can-never-learn-anything theory, how can you leave out these and the many others? Remember, variables rule!
joe b.

[Tiger]

Gibson,

You said: As mentioned, the ballanced bullet is not affected by RPMs centifugal force because there is nothing for the centrifugal force to act upon"

On yes there is, one is air and another is turbulence. Centrifugal force causes a spinning object to push against anything trying to disturb it.

Think to this, which golf ball will travel further: one hit to cause a backspin or one hit to cause a forward spin. Also if you hit the ball to give it a left or right spin, in what direction will it travel?

I think some see a bullet spinning as fast as a Dremel grinder. Take the famous 30-06 with twist 10. Let shoot 100 yards. That is 3600 inches. Means bullet only turns 360 times before it hits the target in matter fraction second. It not like crazy bicycle wheel spinning say 120,000 rpm toward target. It not get much chance, mean time, to spin.

One thing more. Some jacketed bullet actually more accurate at very highest rpms...how you explain this.

Ralf

[leftiye]

Screw threads and rifling ARE both inclined planes. JoeB that's spelled "Bad hair day"? And also there is a very strong possibility that muzzle pressure in B.A.s shortened barrel scenario will make more negative effect than the reduced rpms will improve thangs (almost worth betting on). My best guess.

[Larry Gibson]

Ralf

"You said: As mentioned, the ballanced bullet is not affected by RPMs centifugal force because there is nothing for the centrifugal force to act upon"

On yes there is, one is air and another is turbulence. Centrifugal force causes a spinning object to push against anything trying to disturb it."

Ok, you're talking about drift with regards to the spinning bullet. However if you look at drift of a bullet you'll find it is not the centrifugal force that causes it. It is the friction between the spinning surface of the bullet and the air. As to tubulancethat is a force acting upon the bullet unless you are talking about bullet turbulence, then it wouldn't be stable would it? The centrifugal force from the RPM does not exist outside the bullet.

"Think to this, which golf ball will travel further: one hit to cause a backspin or one hit to cause a forward spin. Also if you hit the ball to give it a left or right spin, in what direction will it travel?"

Again that is drift. The golf balls movement in the direction of spin has to do with the friction of the air on the ball. It has nothing to do with centrifugal force.

"I think some see a bullet spinning as fast as a Dremel grinder. Take the famous 30-06 with twist 10. Let shoot 100 yards. That is 3600 inches. Means bullet only turns 360 times before it hits the target in matter fraction second. It not like crazy bicycle wheel spinning say 120,000 rpm toward target. It not get much chance, mean time, to spin."

You include all theelements of RPM calculation but you fail to factor time in, I. e. the velocity of the bullet. If it was as you say then every bullet out of a 10" twist would have the same RPM to 100 yards. Doesn't work that way. The "M" in RPM stands for "Minute". That means we must convert the fps to to that part of a minute. What that means is the faster the bullet gets to 100 yards the faster it makes those revolutions (the R in RPM). Thus the higher RPM.

"One thing more. Some jacketed bullet actually more accurate at very highest rpms...how you explain this."

Without a specific example it is hard to answer that question. However I will say this that many may appear to be more accurate at higher velocity but could it be simply that the most accurate load for that particular bullet is at higher RPM? Or how about simply that the jacketed bullet isable o withstand the effects of acceleration a hell of a lot better than a cast bullet.

Larry Gibson

[runfiverun]

one more here

how's about a twist gain bbl?
easy on the boolit to start, good acceleration, and predictable rpm's.

no?

how about a choke bore, or a flared end, or one with a tapered bore down to
a tight spot and then tapered back up ?
let larry finish his tests?

larry.
seriously i have thought about a twist gain bbl what say y'all ?

[Larry Gibson]

Screw threads and rifling ARE both inclined planes. JoeB that's spelled "Bad hair day"? And also there is a very strong possibility that muzzle pressure in B.A.s shortened barrel scenario will make more negative effect than the reduced rpms will improve thangs (almost worth betting on). My best guess.

Leftiye

You and Bass bet on it all you want but lopping off 12" of any of the 3 rifles in this test is out of the question for two reasons; one, I'm not going to ruin a perfectly good rifle to disprove a Bassism. Second and most important is lopping of 12" makes them illegal. Like I said Bass could do it if he wants but I'm not. I've shot enough 311291s out of 18" barrel to know the Bassism is wrong. Try it yourself with a 16 or 18" barreled .308 with a 10" twist. You will find that the RPM threshold is there just the same as with the 24" barrel I'm using for this test. The difference is I can use a slower time pressure curve to achieve the same velocity in the longer barrel which means I can push further into the RPM threshold than the shorter barrel. That's one of the "variables" Bass doesn't think is there.

Larry Gibson

[Tiger]

The golf ball goes further with correct direction spin, less pressure area is created which it follows. Something like new bow and hull design on ships cut the water to create a void of water along the length of the hull so ship pass through with less friction.

I realize the time factor with bullet spin, meant it's not spinning complete rpm at those high numbers without moving forward also. The Dremel does not have move to spin fast.

Hard to be specific with jacketed bullets more accurate at higher speed because there are so many examples. Not to do with twist is too slow.

Ralf

[Larry Gibson]

Ralf

I don't claim to know that much about shooting golf balls so I'll take your word for it. However I do know a little about shooting bullets. Drift and its effects are different from the effects of centrifugal force of RPM.

Let's take a 12" twist as the math is easier; the bullet will make 300 revolutions in traveling 100 yards. If it gets there in one second it is turning 18,000 RPM (300 x 60 seconds) If it gets there in 1/10 of a second it is turning 180,000 RPM. There is a lot of difference in centrifugal force there, eh? Thus even though they both turn the same revolutions getting there the higher velocity bullet is actually spinning much faster. If the second bullet had the same flight time of 1 second as the first how many revolutions would it have made? The answer is 3,000. So given 1 seconds of flight time for both bullets the slow bullet makes 300 revolutions and the fast bullet Makes 3,000 revolutions. See the difference?

It is true that some jacketed bullets are more accurate at higher velocity in slower twists but this has to do with rotational stability of the bullet.

Larry Gibson

[Bass Ackward]

The difference is I can use a slower time pressure curve to achieve the same velocity in the longer barrel which means I can push further into the RPM threshold than the shorter barrel. That's one of the "variables" Bass doesn't think is there.[/B]

Larry Gibson


Larry,

Look. I never expected you to lop off one of those barrels. This was another one of those tests if you are interested. But you can use a take off of something you re-barreled, shoot the HV loads in it and record the data and then cut it off. The idea here is NOT to change the load to favor a short barrel. Then you rework the whole dynamics.

This is a down and dirty that should show dramatic improvement if done with a 10 twist. Quickload says that cutting 10" off a 24" barrel should drop a 2500 fps load down to 2000 fps from a 24" tube. That takes you from 180,000 RPMs back down to 140,000. Or adjust the load for 2300 fps and 1800 with the shorter tube and start over so that when you cut it off so that you end up back in .... "the zone" ... that as of yet is to be defined. That should take a 4" group and make it 1" group without any other variable as Joe says. Because the claim here is that RPMs are solely responsible for inaccuracy. So all these little other variations should only add up to maybe a 1 1/2" group at worst according to the RPM theory. I don't think it will, but we could see for sure.

According to the singular focus of accuracy theory occurring at the lowest RPMS, then that means to stay away from 30 calibers in preference to 45 calibers for cast with stronger bullets to resit deformation and can achieve stabilization at the lowest RPMs. In fact, this RPM theory ought to apply to jacketed as well. Look at all those benchresters wasting components with small calibers and over spinning when they could be shooting 45s on up for accuracy competitions. Cause if RPMs is the all powerful accuracy force, then it can't be beaten.

Big bores, with cast or jacketed would ALWAYS be significantly more accurate than small. We can call this a Larryism. :grin:

I sent you an email asking for your email address to send you some pictures that a fella sent me. I have one for a Kathleen Gibson, it that it?

[45 2.1]

Let's take a 12" twist as the math is easier; the bullet will make 300 revolutions in traveling 100 yards. If it gets there in one second it is turning 18,000 RPM (300 x 60 seconds) If it gets there in 1/10 of a second it is turning 180,000 RPM. There is a lot of difference in centrifugal force there, eh? Thus even though they both turn the same revolutions getting there the higher velocity bullet is actually spinning much faster. If the second bullet had the same flight time of 1 second as the first how many revolutions would it have made? The answer is 3,000. So given 1 seconds of flight time for both bullets the slow bullet makes 300 revolutions and the fast bullet Makes 3,000 revolutions. See the difference? Larry Gibson

Rotational velocity is imparted by the barrel twist. It has little to do with forward velocity. The boolit still turns the same amount of revolutions in the same distance regardless of the forward velocity. Rotational velocity is proportional to your centrifugal force. Your example needs amended.

[sundog]

Pressure induces velocity. Increasing pressures induces acceleration. Most standard pressure curves show a peak somewhere in the barrel and then decrease, eventually to standard pressure when the boolit exits. So, the boolit accelerates as pressure increases, and then as the peak is passed it a) maintains velocity as pressure drops, b) continues to accelerate, or c) decelerates. My way of thinking is 'c'.

Felix, what was that barrel length those guys figured out in the Houston warehouse tests? Twenty-one and a half inches?

[Larry Gibson]

45 2.1

The example does not need ammending. You are still leaving the time ellement out. Perhaps you should realise you are wrong and understand the world is not flat. Or put the time element back in as that is what the "Per Minute" means. It is not RPD (Revolutions Per Distance) it is RPM (Revolutions Per Minute).

Larry Gibson

[Larry Gibson]

Bass

You are not readng what I am posting. I have shot plenty of the exact same loads in shorter 16-20" barreled .308s and the RPM threshold remains the same. Another couple inches off he barrel is not going to change anything.

Larry Gibson

[Tiger]

Larry Gibson

Let me throw some things at you. Take your 311291 bullet . Make velocity 2500 fps. That gives us 180,000 rpm. First look too rpm...that means revolutions per minute, yes? According to Lyman time of flight to 100 yard target is .131124 seconds. Bullet is not in flight for one minute. Let us say that it took 1 full second instead of what Lyman say. Then my question to you is did bullet turn 180,000 rpm or did it turn 180,000 rpm divided by the one second which come to 3000 turns?

Let me ask different way. If you could stop bullet right after come out muzzle but not stop rotation, all this for observation purposes, would bullet be actually spinning 180,000 rpm? I think not. Another observation. Guns do not torque very much when fired but they do recoil. If you lay rifle on bench and fire with string would not you think if bullet leaves muzzle at 180,000 rpm that not only would rifle recoil back but spin some too from rotational torque?

Someone say bullet leaving muzzle like soft copper wire spun in drill. This is such crazy comparison to bullet, how do I explain. Bullet is not like spinning flywheel. If bullet is really spinning like that would you not think that this rotational force would show up in certain targets like gel test or flesh? Take a flat plate aluminum. Put it on drill stand table but no clamps. Chuck in 1/2 inch drill and set drill rpm for say 2000 rpm. Then abruptly bring drill down fast into aluminum. What happen? Aluminun gets spun very violently. Yet bullets don't show this in target medium.

I think what I am getting at is not rpm that destroys accuracy or bullet for that fact but I think pressure.

One more thing think Larry. I have seen test where noses of jacketed bullet were damaged to see what happens. You would think the bend noses would unbalance bullet badly but yet they shot say ok. I don't like that voids unbalance bullet so bad and is amplified by rpm because I don't think bullet is really spinning that fast.

You go think and let us know what you come up with to my many questions.

Ralf

[Larry Gibson]

Sundog

Actually there is not "standard" pressure at bullet exit, there is still considerable pressure pushing on the bullet. The bullet is still increasing in velocity as the pressure drops from peak pressure. It does not "maintain" (or coast along) velocity in the barrel. There are some exceptions, i.e cases with very small capacity like the .22LR or perhaps large cases with very small charges of powder. However with the cartridges, pressures and velocities we are discussing the bullet continues to increase in velocity all the way to the end of the barrel.

The correct answer is "b".

Larry Gibson

[sundog]

When referring to 'standard' pressure, what I meant was atmospheric pressure.

I still think the correct answer is 'c'. How can a boolit be accelerating with decreasing pressure? Then, too, there is friction working against it. At best it can only maintain what velocity it has.

I'm not being argumentative. What this is about is the 'damage' that occurs to the boolit as it passes through the barrel, where the damage occurs, how much, and what further damage occurs. If everything were 'good-to-go' accuracy would be a non-issue. So, we take a 'perfect' boolit, barrel, etc., and it ain't so perfect accuracy. What happened? Of course, that's what you are testing. I'm just wondering where all the damage is taking place.

[Larry Gibson]

Ralf

Let me throw some things at you. Take your 311291 bullet . Make velocity 2500 fps. That gives us 180,000 rpm. First look too rpm...that means revolutions per minute, yes? According to Lyman time of flight to 100 yard target is .131124 seconds. Bullet is not in flight for one minute. Let us say that it took 1 full second instead of what Lyman say. Then my question to you is did bullet turn 180,000 rpm or did it turn 180,000 rpm divided by the one second which come to 3000 turns?

That is correct; you are dividing the 180,000 by 60 (60 seconds in one minute) to get the RPM of one second, i.e. 3,000.

Let me ask different way. If you could stop bullet right after come out muzzle but not stop rotation, all this for observation purposes, would bullet be actually spinning 180,000 rpm? I think not. Another observation. Guns do not torque very much when fired but they do recoil. If you lay rifle on bench and fire with string would not you think if bullet leaves muzzle at 180,000 rpm that not only would rifle recoil back but spin some too from rotational torque?

If you stop the rotation you are correct, the bullet is no longer doing 180,000 RPM. It is doing zero RPM because you stopped it. I'm not seeing a point to this?

There is in fact torque. Shoot a light weiht '06 with a 180 gr bullet without holding the rifle and you will see the rifle recoil to the rear and counter clockwise. Also ask any big bore shooter if there is no torque during recoil. Yes there is torque. However it is proportional to the weight of the bullet, the spin, the velocity and the weight of the rifle. As I mentioned earlier about higher pressure in faster twists. There is higher pressure as the bullet enters the rifling. That also is where the rifle is torques. Some question whether there is further resistance or torque be cause once the bullet is in motion (rotating) in tends to stay in motion. I'm not really sure either was but as I've said; I've not found any evidence on bullets of increased pressure in the rifle marks on fired bullets.

Someone say bullet leaving muzzle like soft copper wire spun in drill. This is such crazy comparison to bullet, how do I explain. Bullet is not like spinning flywheel. If bullet is really spinning like that would you not think that this rotational force would show up in certain targets like gel test or flesh? Take a flat plate aluminum. Put it on drill stand table but no clamps. Chuck in 1/2 inch drill and set drill rpm for say 2000 rpm. Then abruptly bring drill down fast into aluminum. What happen? Aluminun gets spun very violently. Yet bullets don't show this in target medium.

I think what I am getting at is not rpm that destroys accuracy or bullet for that fact but I think pressure.

That's what most every one thinks. Hoever (once again) Pressure effects the bullet in the barrel. RPM effects the bullet in flight. If there was no centrifugal force from RPM then all bullets, even unbalanced bullets, would fly straight. Of course youstill have the effects of wind on the bullet but it is the centrifugal force of the RPM that causes the inaccuracy.

One more thing think Larry. I have seen test where noses of jacketed bullet were damaged to see what happens. You would think the bend noses would unbalance bullet badly but yet they shot say ok. I don't like that voids unbalance bullet so bad and is amplified by rpm because I don't think bullet is really spinning that fast.

You go think and let us know what you come up with to my many questions.

I don't have to go think. You go back and reread this thread and the first thread, Chapte 1. You will find I purposely unbalanced some .308 bullets and fired "before" and "after" ten shot grups. Study them closely, the answer is obvious.

Damaging the nose does unbalance a bullet but not "badly" Shootin "ok" as compared to what? If they shoot into 1 moa undamaged and into 3 moa damaged is that "ok"? It may be for deer hunting but it is not to a measurement of accuracy.

Larry Gibson

[felix]

That's true, Corky. Maybe it was 21 and 3/4. Talking strickly vibes here with a free floated barrel in any caliber they tested. This observation assumes projectiles at 3300 fps and the force required to make that speed. It seems that 300 fps increments provided the "same" vibe trace. We always want the projectile to leave the barrel when the barrel exit is not moving, so the length of the barrel must be exactly at a half-node location. We know in practice that will never happen because that location is so small in the trace, and the acceleration of the vibe is maximum at that point, even though the velocity is zero. The opposite at a nodal location, so we never want to chop a barrel off at a vibe node. ... felix

Remember, this is about free float without a Boss or any kind of weight at barrel end.

[sundog]

"If you could stop bullet right after come out muzzle but not stop rotation, all this for observation purposes, would bullet be actually spinning 180,000 rpm?"

Yes. Put it like this. If the boolit remained in flight for one minute, other than bleeding off some rpm due to external influence (kinda like a top slowing down), it would be expected that it would turn 180,000 times in one minute.

Don't confuse rpm with number of turns in a given distance. The number of turns in a given distance is fixed, a constant, by the rifling. In one hundred yards (300 hundred feet) a boolit from a 12 twist barrel (one turn in one foot) will turn 300 times, regardless of velocity.

[45 2.1]

45 2.1

The example does not need ammending. You are still leaving the time ellement out. Perhaps you should realise you are wrong and understand the world is not flat. Or put the time element back in as that is what the "Per Minute" means. It is not RPD (Revolutions Per Distance) it is RPM (Revolutions Per Minute).

Larry Gibson

See if you can get this: Revolutions per distance traveled do not change even when velocity is varied. Time has no relevance in that regard. If you chose to make up things, your results will be made up also.

[felix]

The RATE of projectile ACCELERATION changes direction at circa 16 inches. This is the third derivitive of the distance traveled over time. Could be the reason they decided a pistol was defined to be anything under 16 inches. Speculation on my part. Somebody must have lobbied somebody for that specific length. ... felix

[felix]

True, Bob. Distance and time must be considered as the only elemental parameters in your discussion, Larry, about what you are talking about. Velocity is nothing but a function of both. ... felix

[Tiger]

This from internet: An object traveling in a circle behaves as if it is experiencing an outward force. This force, known as the centrifugal force, depends on the mass of the object, the speed of rotation, and the distance from the center. The more massive the object, the greater the force; the greater the speed of the object, the greater the force; and the greater the distance from the center, the greater the force.

With that said I think smaller diameter bullets have less force on their outer surface then larger calibers. Then how does this explain the forums famous 6.5 Swede bullets not being able to be shot at high velocity, according to the above centrifugal force law?

RPM can be viewd, I think, both as a speed and as a counter. I explain. As in speed this would relate to a flywheel...how fast it is spinning. Now put a paint marker on the outer edge of the flywheel and use it to count how many revolutions the flywheel makes in one minute. See what I mean?

In nut shell: I do not believe bullet is spinnning the rpms figured out by the rpm formula. I believe it only turns number of rpm's (as in the counting method I explained above) given it by the rifling twist in the barrel.

Another internet taking: An object traveling in a circle behaves as if it is experiencing an outward force. This force, known as the centrifugal force, depends on the mass of the object, the speed of rotation, and the distance from the center. The more massive the object, the greater the force; the greater the speed of the object, the greater the force; and the greater the distance from the center, the greater the force.

With that said we are looking at tensile strength. Larry if you thing the bullet alloy tensile strength "just begins" to let the bullet deform after the rpm ceiling you have imposed, then why does the bullet disintegrate in a ridiculous rpm figure like over 200,000 rpm? Mine you, you claim that the rpm is starting to do something to the bullet after your rpm ceiling limit.

You need to look else where then rpm causing accuracy problem, this is of course if the rifling rate is correct for the bullet length and weight.

Ralf

[sundog]

Tiger, if your flywheel is turning 12 rpm it will turn 12 times in one minute or 1 time every 5 seconds. During that 5 seconds (and even if it's the ONLY turn it makes), it is still turning 12 rpm, even though it only turned one time.

[Tiger]

Sundog,

I know that. I meant as in the flywheel it is spinning at some rpm. The other I meant like a friend is going to turn shaft connected to a set of gears and he ask you watch output shaft how many time or complete revolutions it turns as he turns the input shaft. See?

Ralf

[felix]

This might help. Take a 100 grainer at 22 caliber versus one at a 45 caliber, both shot at 16 twist with the same barrel length. How much powder energy (powder speed optimized for bore) will it take each to make each projectile independently go 1600 fps? This will decipher how much energy it took to rotate the outermost particle on each projectile to reach the same RPM. ... felix

[HORNET]

If you spin the boolit up to 180000 rpm out of a 12" twist at 2500 fps, then its turning at 180000 rpm regardless of what the forward velocity may change to subsequently. If it slows to 1250 fps, its still turning 1800000 rpm but only traveling half as far during the same amount of time. This would now give it 1 turn in 6"... think about it.
Sundog, the boolit will continue accelerating in the barrel as long as the force exerted on the base by the pressure (F= pressure x area) exceeds the friction (F=Mass x Acceleration). The required pressure can be remarkably low as in the cat-sneeze loads.

[felix]

Any one particle on the boolit accelerates the same down the axis of the barrel. But, the particle in the center of the boolit has zero lateral distance to move, and therefore cannot have any lateral acceleration or velocity. ... felix

[sundog]

The boolit accelerates as pressure is decreasing?

Then how do you explain stuck boolits? In order to get stuck, it had to slow down.

And what about those crazy secondary spikes on pressure trace graphs?

[felix]

Impossible, Corky. Stuck boolit is equal to zero dynamic pressure. Static pressure is released as you uncork the beer bottle (or open the action, assuming the action caused a perfect seal). Get the barrel long enough, then we will get a stuck boolit. ... felix

[sundog]

That's what I'm saying. Friction overcomes pressure, boolit stops. There had to be pressure to get it going, eh?

[leftiye]

Sundog, I really hate to help larry out here, he is so good at bending or ignoring what was said that he really needs no help. But where the wires got crossed here with the pressures decreasing thing (after the peak of the pressure curve) is that though the pressures becomes lower after the peak pressures occur, they are still plenty high enough to further accelerate the boolit. A lot of the magnum cartridges have exit ressures in a longer (26")barrel of about 7000 psi (from memory -30 years old data), enough to push a boolit through a bore (maybe not engrave it though) and to continue accelerating it. Yep, acceleration, and increasing revolution rate occur clear to the muzzle.

Larry, as Bass said no one even thought for a moment of suggestion that you cut the barrels off of your guns. Nor is the question of whether or not such shortened barrels would be legal an issue here. The proposition was a theoretical one suggesting that while the RPMs would decrease to ideal levels, the exit pressures might totally destroy accuracy, or at least offset any gain from lower rpms.

Bass also has good points in saying that the rpm effect should show up with jacketed bullets too [ It actually should effect all bullets, as with my previous post about why come the paper patched boolits can be shot so fast and still not lose accuracy - This has to be that plain lead boolits recieve much more deformation than is visible, and any sort of protection from the bore will reduce this] and also that the lower RPMs encountered in larger, slower velocity, slower twist calibers should make them better candidates as accuracy guns than small bore calibers.

[sundog]

Leftiye... no, pressure is still plenty high enough to force the boolit out of the barrel in a normal situation. I don't see how decreasing pressure can equate to acceleration.

Apparently the frog thinks deceleration is possible, too. About 2/3 the way down under the pressure curve graph.

http://www.frfrogspad.com/intballi.htm

[felix]

Yep, Corky, that would be close to 16 inches. Keep in mind the frog is talking about the RATE of the pressure change reversing directions, and not the pressure itself. It is still being generated, but now at a decreasing rate. ... felix

[joeb33050]

[QUOTE=sundog;321310] I don't see how decreasing pressure can equate to acceleration.

QUOTE]

Say the bullet's going 37 fps and pressure falls from one zillion psi to .999999 zillion psi. The bullet accelerates to 38 fps in some (small) bit of time.
joe b.

[sundog]

Yeah, so if the peak is too early you have exactly what I'm talking about.

Remember the stuck boolit? If the peak were later, the boolit might clear the muzzle.

[joeb33050]

Rotational velocity is imparted by the barrel twist. It has little to do with forward velocity. The boolit still turns the same amount of revolutions in the same distance regardless of the forward velocity. Rotational velocity is proportional to your centrifugal force. Your example needs amended.

45 2.1 is talking about Revolutions per distance traveled. Call it R/S, where distance is S. In a 1' 12" twist barrel, the bullet turns one revolution per 12" = 1 R/1 Foot.
Larry is talking about RPM = Revolutions/1 minute.
It is easy to operate here if one writes down the UNITS.
When one does this kind of arithmetic, it is necessary to put down the UNITS, and do arithmetic to the units as well as the numbers.
Bullet RPM = Revolutions/(1)Minute. Etc.
If you put the UNITS down, it is easy to solve for any unknown within those units.
This ain't algebra and it ain't physics. It's cast bullets.
Anyone who wants to know the answer to any question within the RPM, Twist, MV, Distance set of units, PM me the question and I'll give you the answer and how it is derived.
Felix can do the same. Others also.
UNITS are a physicist's trick, other scientists and mathematicians also. Normal people aren't aware of the importance of UNITS cause they don't do these calculations.
UNITS, ya gotta write them down, or you get answers that look funny because the (invisible if the calculator doesn't write them down) units end up as "minutes per inch of twist", or something equally meaningless.
joe b.

[joeb33050]

Ralf

centrifugal force of RPM.

Let's take a 12" twist as the math is easier; the bullet will make 300 revolutions in traveling 100 yards. If it gets there in one second it is turning 18,000 RPM (300 x 60 seconds) If it gets there in 1/10 of a second it is turning 180,000 RPM. There is a lot of difference in centrifugal force there, eh? Thus even though they both turn the same revolutions getting there the higher velocity bullet is actually spinning much faster. If the second bullet had the same flight time of 1 second as the first how many revolutions would it have made? The answer is 3,000. So given 1 seconds of flight time for both bullets the slow bullet makes 300 revolutions and the fast bullet Makes 3,000 revolutions. See the difference?

It is true that some jacketed bullets are more accurate at higher velocity in slower twists but this has to do with rotational stability of the bullet.
Larry Gibson

I can't find any error here. The 1/10 second 100 yard bullet is averaging 3000 fps and turning 180000 rpm = 3000 rps. . No matter how it slows down, in 1 second it will turn 3000 revolutions per second, If I did it right.
Except that there's no such thing as centrifugal force. Centripetal.
joe b.

[45 2.1]

Except that there's no such thing as centrifugal force. Centripetal. joe b.

Here is something for you to read Joe.

http://en.wikipedia.org/wiki/Centrifugal_force

[sundog]

okay, Joe, I understand fully. "It's cast bullets." Excuse the hell outa me for having a discussion!

[Larry Gibson]

sundog

I still think the correct answer is 'c'. How can a boolit be accelerating with decreasing pressure? Then, too, there is friction working against it. At best it can only maintain what velocity it has.

Think about it, the pressure may be decreasing but it is still greater pressure than the minimal friction can hold back and greater pressure than the air in front of the bullet. Thus the bullet continues to increase in velocity. Lets say the pressure peaks at 12" of bullet travel. If we took a 24" barrel and the velocity was 2500 fps and we cut the barrel off 2" at a time would the velocity remain 2500 fps until we cut the barrel to 12"? No it would not, you know that and so oes everyone else. Velocity would drop a corresponding amount with each 2" we cut off. The remaining velocity at 12" of barrel travel and at peak pressure would be far less than 2500 fps. That is because the bullet continues to increase in velocity until it exits the barrel.

I'm not being argumentative. What this is about is the 'damage' that occurs to the boolit as it passes through the barrel, where the damage occurs, how much, and what further damage occurs. If everything were 'good-to-go' accuracy would be a non-issue. So, we take a 'perfect' boolit, barrel, etc., and it ain't so perfect accuracy. What happened? Of course, that's what you are testing. I'm just wondering where all the damage is taking place.

The damage takes place in the barrel during accelleration, Most of it will occur before peak pressure is reached.

Larry Gibson

[Larry Gibson]

Here is something for you to read Joe.

http://en.wikipedia.org/wiki/Centrifugal_force

45 2.1

I was waiting for someone to bring up wikpedia. Do you really believe what gets posted in wikpedia?

Larry Gibson

[Larry Gibson]

joe b

Same meaning, different terminology.

Larry Gibson

[405]

Yep, I think this always gets some shorts in knots.

It's my undertanding that "centrifugal" force is like angular momentum (maybe better term?) and "centripetal" force is the force required to hold something together that is being slunged (:mrgreen:) outward by "centrifugal" force (angular momentum). In this case centripetal force can be viewed as the cumulative molecular bonds holding the bullet together while the bullet is spinning in free flight.

Could be all wrong but IIRC that's the way I lernt it :coffee:

[sundog]

Larry, since I started it, you wanna save the a,b, or c for later. Let's agree that the major damage probably occurs early on. Nice, fresh 'perfect' boolit gets slammed into some screws. I'm not for sure the 'how hard' it gets slammed makes all that much difference, unless it's TOO hard and gets immediately stripped. Even a HT or WQ boolit is going to be rearranged. Peak pressure does not occur, at least with medium and slower rifle powders until down the barrel some distance. So, early on that rising pressure may not really look all that much different powder to powder, charge to charge although the final peak pressure may be different in time or psi or both. Boolit still gets slammed up against the screws and forms to meet them. Ten BHn or 24 BHn, it still gets swaged into the barrel. Maybe what would be interesting is to recover like boolits from like loads with the ONLY difference be hardness and see how they have changed. Other than harmonics, what I'm getting at is that if internal ballistics are okay across the variances, then the problem can be discovered elsewhere, i.e., externally. Any of that make any sense?

[Larry Gibson]

sundog

Makes a lot of sense. Actually the M43 lets you "see" the time pressure curve and how it does in fact look radically different as the powder to powder and charge to charges change. Wish I could post more of them. I am up in Alaska right now so I'm not able to. Perhaps when I get back home I can share more of the information I am gaining from the M43. Will be interesting to compare the measurements of different hardness of bullets and see how getting slammed against the screws really affects them. That is the basis of my belief that the inaccuracy results externally. The imbalances may be created internally but the force that causes the inaccuracies is external.

Larry Gibson

[leftiye]

Sundog, Plus 1 on the damage ocurring early on (at least a large proportion of it). We've talked about it here on this board mostly as if the engraving (and before) were a part of the acceleration. I even posted a thread saying that acceleration RATE was the issue causing the deformation when it acted against the inertia of the frontal pars of the boolit.

[This happens before there is any rate of acceleration.] But it is probable that we should look at the boolit at the start as not just being immobile, but as being caught against an obstacle (the beginning of the riflng, I won't say leade, some guns don't have a leade) and as being during that time crushed against that obstacle by the pressure of the burningpowder. I think this is important because it portrays the bullet in that state as being literally crushed out of shape by the pressure.

[joeb33050]

okay, Joe, I understand fully. "It's cast bullets." Excuse the hell outa me for having a discussion!

Sundog;
Discuss what you will. It bothers me that much/some of this disussion revolves about confusion or lack of precise knowledge of scientific and/or mathematical stuff. I attempted to point this out, and also say that "this ain't science, it's cast bullets", suggesting-I thought-that the folks on this forum are NOT scientists or mathematicians for the most part, and shouldn't be expected to be facile with the mathematiocs involved. And I knew that someone would take offense.

In the book I put a workbook and explanation of the specific gravity of lead-tin-antimony alloys; and a suggestion that finding the specific gravity of an unknown alloy and using the workbook, one might be able to make an educated guess as to the alloy composition.
Later, here, on this forum, a poster helped me to correct my wrong workbook. I had assumed that alloy specific gravity was the weighted average of the constituents; but was shown that the alloy specific gravity is the weighted harmonic mean of the constituents. To check this new (to me) information I did the algebra with the UNITS and easily saw my mistake.
UNITS matter.
joe b.

[joeb33050]

Here is something for you to read Joe.

http://en.wikipedia.org/wiki/Centrifugal_force

A little googling and you can see that the physicists are unanimous on this. Here's one excerpt from the regents exam site.

"An evil word has worked its way into our daily vocabulary, and with it, an incorrect understanding of the way physics works. "Centrifugal Force" ( Latin for "center fleeing") is often used to describe why mud gets spun off a spinning tire, or water gets pushed out of the clothes during the spin dry cycle of your washer. It is also used to describe why we tend to slide to the outer side of a car going around a curve. It is a common explanation...the only problem is all of it is absolutely wrong!!! Centrifugal force does not exist...there is no such thing...it is a ghost we tend to blame odd behavior on."

joe b.

[45 2.1]

45 2.1

I was waiting for someone to bring up wikpedia. Do you really believe what gets posted in wikpedia?

Larry Gibson

Its a nice non-technical explanation that is fair, as far as it goes. Joe's comment was that it doesn't exist, which is untrue. It is also published, something that your writings are NOT, except for here. If your so good with your information, get it PUBLISHED in the "Fouling Shot" and in the ASSRA journals and see where it leads.

If you want to keep talking about high RPM numbers, bring it into context: 10" twist with Time of flight (TOF) at 100 yds for: 2400 fps = 100 yds x 3 ft/yd / 2400 fps = 0.125 seconds. For 1600 fps TOF = 100 yds x 3 ft/yd / 1600 fps = 0.1875 seconds. RPM (2400 fps) = 2400 x 72 = 172,800 RPM x 0.125 seconds / 60 seconds/min = 360 revolutions. RPM (1600 fps) = 1600 x 72 = 115,200 RPM x 0.1875 seconds / 60 seconds/min = 360 revolutions. All this ignoring external wind and gravity effects to keep it simpler (much like your rounding of RPM numbers).

Hmmmmmm........ RPMs got you..??, with the same number of revolutions to target? The only difference is Velocity. You mean Velocity got you. RPM is a meaningless number here since the boolit IS NOT spinning faster in either case. They are spinning/rotating/revolving at the same rate per distance traveled. This is why i'm calling BS to your assertion about RPMs being the culprit. If you want to contend that velocity (along with pressure involved and boolit fit) is the problem, then you would be on the right track.

[45 2.1]

A little googling and you can see that the physicists are unanimous on this. Here's one excerpt from the regents exam site.

"An evil word has worked its way into our daily vocabulary, and with it, an incorrect understanding of the way physics works. "Centrifugal Force" ( Latin for "center fleeing") is often used to describe why mud gets spun off a spinning tire, or water gets pushed out of the clothes during the spin dry cycle of your washer. It is also used to describe why we tend to slide to the outer side of a car going around a curve. It is a common explanation...the only problem is all of it is absolutely wrong!!! Centrifugal force does not exist...there is no such thing...it is a ghost we tend to blame odd behavior on."

joe b.


Much like the use of the term "Bore" that is commonly used here, meaning Groove diameter. Not the same thing, but commonly used. Much like your usage of "Headspace" Joe. Ahh, the non-technical describing technical terms and there usage. The force does exist, but is called several other things dependent on the application its used in.

[Larry Gibson]

Much like the use of the term "Bore" that is commonly used here, meaning Groove diameter. Not the same thing, but commonly used. Much like your usage of "Headspace" Joe. Ahh, the non-technical describing technical terms and there usage. The force does exist, but is called several other things dependent on the application its used in.

4 2.1 and I are in agreement here. I may or may not submit it for "publishing". However the test is not complete and thus it wouldn't get published until it is complete. Some also consider posting on the internet (like on this forum) as "publishing". Whether published here or elsewhere in print does not make something fact. All it means is that it was published just like the many falsehoods and opinions in wikpedia. I am conducting tests and publishing the results. The facts speak for themselves.

As to your dissertation on RPM; are you kidding? Reducing fps to 1600 fps from 2500 fps muzzle velocity based on TOF to 100 yards is really out there in left field. The calculated RPM of a bullet from a 10" twist at 2500 fps is around [yes I am rounding off these days as someone (care to guess who?) may want to argue about the nth degree] 180,000 fps. That is the correct answer regardless of how you want to cogitate it.

If it was "velocity" (I thought you were on the "it's pressure" bandwagon?) then explain why at equal velocity with equal pressure the accuracy of the 10" gets proportionally worse that the 12" twist. And tell me why the 12" twist gets proportionally worse than the 14" twist". The facts are there regardless of how you cogitate it. It is RPM.

Larry Gibson

[Bass Ackward]

Been doing more thinking. The whole case against the pressure theory here that by default is supposed to support the RPM theory is a device that is "glued" to a piece of steel. The imperfect results of this from everything like surface tension variance of the barrels to consistent steel thickness over the chambers is fed to a computer with a program written by a human who says ignore this stuff and if you move this much, draw this picture. Has the Bureau of Standards adopted this method as the final answer for pressure? I don't think so.

Look, the worst accuracy we generally get with cast bullets is from a pressure related phenom known as the "keyhole". Here a bullets flight is distorted enough that regardless of the RPM rate it is spinning, (slow, medium, or fast) the bullet is tipped upon exit to the point where RPMs are insufficient to ever get it to go to sleep or stabilize. Keyholes often can't be held on paper at 50 yards. The negative force here is muzzle pressure.

Now I am not naive to believe that we go from a perfectly terrible state of key-holing to a perfectly perfect rotational state, that RPMs is the only force affecting that slug. There has to be a transition. We know how aerodynamics affects planes, so it has to have some effect when we change the name and call it ballistic coefficient. So I am not naive to believe wind has no effect here on either force and that the longer or worse a slug is tipped or wobbled off by RPMs that it will shoot well regardless of the twist rate we launch it.

Therefore, you get a sliding scale between these forces with less and less of an effect from one to the other where pressure minimizes and RPM forces begin to take over and visa versa. IN the null between these we get a perfect launch situation where you get the best ballistic coefficient of a slug flying directly forward.

As Joeb always says, there are too many variables to calculate this out. If we make a harder bullet or a stronger design or slow the pressure curve to maintain bullet integrity, we minimize each of these effects to where neither affects accuracy enough to argue about.

[felix]

I am not sure, Larry, that if RPM is the problem (it is to some extent, for sure) outside of the barrel. When it is all said and done, it seems to me that problems exist on how the RPM is generated. Sorta' like using Corky's take on the problem. The more you get screwed (internal), the more badly you feel after the deed had beens done (external). It is going to be difficult to explain why some guns shoot equally well at 2700, for example, as they do at 2400 using the same twist. Vibes? Can't leave that synopsis out either unless we have a gun that has a BOSS attatchment which makes the "correct" vibes at 2700 as it does at 2400. Anyway, let's keep the tests going, and I will support you until YOU cry "Uncle". ... felix

[45 2.1]

Sundog, I really hate to help larry out here, he is so good at bending or ignoring what was said that he really needs no help.

I do believe that leftiye is quite correct in his statement about Larry.





Now to Larry:

As to your dissertation on RPM; are you kidding? Not a bit. Reducing fps to 1600 fps from 2500 fps muzzle velocity based on TOF to 100 yards is really out there in left field. I don't know how to make out your sentence as it makes no sense like it is, but my post is standard stuff. Not made up a bit. Just a proof to all who are reading so they can check it out for themselves. Same amount of revolutions iregardless of velocity at the same distance. The calculated RPM of a bullet from a 10" twist at 2500 fps is around [yes I am rounding off these days as someone (care to guess who?) may want to argue about the nth degree] 180,000 fps. What is this, is it supposed to be RPMs? That is the correct answer regardless of how you want to cogitate it. I don't think RPMs are measured in fps as you posted. Maybe Joe will offer the use of his RPM calculator to you so you don't have to do any hard stuff and we can all work with the same answer.

If it was "velocity" (I thought you were on the "it's pressure" bandwagon?) You've mistaken me with Bass. He has been talking more about pressure than I have. Go back and confirm it, it is all there to read. then explain why at equal velocity with equal pressure the accuracy of the 10" gets proportionally worse that the 12" twist. I'm sure you are having that problem. The cause is in question though. Several of us aren't having that problem though. And tell me why the 12" twist gets proportionally worse than the 14" twist". The facts are there regardless of how you cogitate it. It is RPM. So you say and unproven so far. RPM is a function of a constant (twist for an individual rifle), a variable (velocity) and a conversion factor which is a constant. Velocity is the only thing you can play with in the equation, so the resultant (which is the RPM number) is a function of Velocity. You have your tests to complete and report on so it can be "cogitated on" as you say.

[Larry Gibson]

Thanks felix.

Assuming your talking jacketed bullets as I've not seen a 10" twist rifle shoot cast bullets as well at 2700 fps as they do at 2400 fps (unless both groups are horribly bad;-)

Larry Gibson

[felix]

That is true, Larry, and that is the point here. We just have to make the groups the same somehow, someway. Don't care about absolute values here. We have to be over the calculated "threshold" to show some "advancement" here. I would suggest from seeing the warehouse shenanigans that we keep velocity in 300 fps increments (maintaining even harmonics; avoiding odd harmonics) to help us keep away from having to use a BOSS gadget to make things work. For example, if you want to keep the RPM range down for this test, that would be OK too, but choose a softer lead to mimic the higher velocities. ... felix

[Larry Gibson]

45 2.1

"So you say and unproven so far. RPM is a function of a constant (twist for an individual rifle), a variable (velocity) and a conversion factor which is a constant. Velocity is the only thing you can play with in the equation, so the resultant (which is the RPM number) is a function of Velocity."

That is exactly what I and others have been telling you. Velocity is the variable. As you increase or decrease velocity the RPM changes. RPM is not a constant based only on how many turns the bullet makes in a certain distance.

I'm not bending or ignoring anything. I deal with facts and they are presented as the result of the tests. It is you who are ignoring those obvious facts. I ask a question based on what you say and when you see how rediculous it was you say "I don't know how to make out your sentence as it makes no sense like it is ". You always come back with BS answers like that. You come up with ideas, cogitations or theories that go from sublime to rediculous and expect me to give them credence when you are just argumentative or are ignoring the facts? I think not.

The test will continue and will be completed. Quite frankly I expect arguement from you regardless of the results. I am weary of these arguements as they serve no purpose. If you have actual test results that confirm your left field cogitations then please present them.

Discussion is over.


Larry Gibson

[joeb33050]

We've got a lot of folks offering opinions and arguing, with no data except Larry's.
We of the experiment by holding everything else constant and changing one variable(ex twist) wihin the bounds of the time and $$ constraints.
Larry is going to send me the data after a while, and is going to test more.
Why go on, sometimes being nasty, when the data will tell the story.
Am I missing something?
I put test protocols and results up here, looking for the/my error/mistake; so I won't test mistakenly.
I hope that Larry will let me publish his results in the book.
Calm
joe b.

[Larry Gibson]

That is true, Larry, and that is the point here. We just have to make the groups the same somehow, someway. Don't care about absolute values here. We have to be over the calculated "threshold" to show some "advancement" here. I would suggest from seeing the warehouse shenanigans that we keep velocity in 300 fps increments (maintaining even harmonics; avoiding odd harmonics) to help us keep away from having to use a BOSS gadget to make things work. For example, if you want to keep the RPM range down for this test, that would be OK too, but choose a softer lead to mimic the higher velocities. ... felix

I agree (contrary to above posts, eh?). First I think it is necessary to establish the existance of the RPM threshold. Then we can see what it takes to bump it up orpush through it. With that knowledge when someone asks why they're not getting accuracy above 1900 fps out of their '06 with 311291 or a similar bullet we can give a correct answer. The way it is now we do not have the answer. I am seeking the answer.

Larry Gibson

[runfiverun]

well i was on the fence here. but i think larry is right!
a had to think of it as obturation in the air, if the bbl is not there to contain
the boolit it gets larger, [ perhaps more so on one side then the other ]
i believe this also will explain why a 50yd boolit is not alwways a 100 yd boolit
time, more time to work the boolit out of shape.

this would explain some of bass's data on his twist shoot
and why the wqww's would shoot better [ harder out side of boolit]
able to contain rotational forces.

internal forces explain why sometimes the rifle will shoot better
and external explains where it all goes wrong.
both are effected by twist rate, and the pressure applied at the start.
however i do not think that even if you could go to 2700 fps at a pressure
of like 30,000. you would always be able to get accuracy?

am i wrong on this?

[Larry Gibson]

joe b

I think your book would be a great place for this test. We would have to edit the comentary a bit to take out comments made directly to members here. Make it generalised to who ever is reading it so to speak.

Larry Gibson

[felix]

R5R, that is exactly what we are trying to find out! ... felix

[Larry Gibson]

runfiverun

You are headed in the right drection. I also think 2700 fps with very good accuracy is quite feasable. Would take a 14 or maybe 16" twist though. I'm thinking of trying to get there with a very accurate 22-250 M700 I have. It has the 14" twist and case capcity for slow powders. The bullet may not have enough weight to burn them efficiently though. Would be interesting to see how the '06 fairs with a 14" twist or even a 16" twist. Bass may be right as I believe he discussed that combination in the past discussions.

Larry Gibson

[felix]

The problem with the 22's is the dirt accumulation commensurate with the slow powders. If you can get 3 shots off with making the boolits touch at a hunnert after a cleaning job, then the test would be valid. Keep in mind that most 22 barrels have shallow lands. Use slow V-V powders for this experiment. Unfortunately, $$$$$. ... felix

[45 2.1]

If you have actual test results that confirm your left field cogitations then please present them. Larry Gibson

Dr Franklin Mann's book "The Bullets Flight". He spent a lot more time and money than I have or you will on the subject.

[leftiye]

Right off the mark, I thought that run5run's idea of boolits obturating while in flight was a little impossible. No pressure to obturate them. But when you think that at about 3300 fps a plain lead boolit is likely to leave a smoke trail and dissapear, then maybe there is a possibility (probability) that deformation is taking place at somewhat lower velocities. This would be even if they're not making smoke, but due to being softened enough by heat due to friction with the air that pressure from the oncoming air can deform them. Hard leads melt at roughly the same temps that other leads do (or even lower maybe).

This is like what happens to the base of a plain base boolit. Using gas checks, and COW, or card wads shows us that the base does either melt a little, or just plain displace from pressure/heat when unprotected. Pressure alone may be below the plastic limit of the lead, but what about when you add heat, maybe not enough to melt the base, but enough to make the base soft enough to flow?

We may have found yet another factor that occurs during flight as velocity increases to add to aerodynamic faults that affect accuracy. This would be a true barrier.

[tube_ee]

Just an engineer with delusions of competence.

If we assume, for the moment, that the reason for the observed phenomenon that cast bullets tend to be less accurate at high velocities than jacketed bullets of similar weight and shape is that the tangential velocity of the bullet causes instability in flight, as the rotational forces act on an unequal mass distribution, then we still need to find out why this seems to affect cast bullets more than jacketed, and from that, derive correction measures so that we can shoot our (cheaper) cast bullets at the same velocity and accuracy as the more expensive jacketed ones. Otherwise, why bother in the first place?

Since RPM of the bullet is a linear function of twist rate (revolutions per unit distance) and velocity (distance per unit time), or, mathematically, r/d * d/t = r/t, it is clear that the issue is not the RPMs per se, but rather the bullet's reaction to those forces. So why is a jacketed bullet more able to resist those forces?

I'll divide this into two sections. First, differences between the ways the two bullets are made, and second, differences in the ways they react to the stresses of firing.

Making bullets: Cast bullets are, well... cast. Liquid metal is pured into a mold, and allowed to solidify within that shape, with no external pressure applied. As I understand it, jacketed bullets are cold-formed under pressure from solid (extruded?) lead and thin-sheet copper. The pressure of forming would tend to reduce uneven distributions of material, and would also likely drive any remaining inconsistencies toward the center of the bullet, and thus closer to the axis of rotation, thus reducing the force acting upon them at a given RPM. BTW, if that's true, then a smaller-diameter cast bullet should be more accurate at a given RPM than a larger one (assume the same BC, SD, and defect rate), since all defects would be experience less force. Has this been demonstrated?

So to control this aspect, we would need to make more internally consistent bullets. Can this be done by changing alloys for more consistent mold fill, somehow improving the evenness of the alloy mix (to get a more even density distribution through the bullet), or anything else that the caster can do, or is some sort of pressurized mold design needed? I'm picturing in my head a mold with a slightly deeper than final sized cavity, and some sort of plunger arrangement on the sprue plate.

Shooting issues: This seems to me to be primarily a surface hardness issue. Copper is much harder than lead, so if a copper-jacketed bullet and a lead bullet (swaged or cast) are shot through the same barrel at the same speed, the jacketed one will emerge from the barrel less deformed (and thus closer to it's original mass distribution) than the lead one. If this is what's happening, then there should be a clearly measurable improvement in accuracy at high RPMs from a harder bullet. And it would seem that those changes should be nearly linear, unless hardness measurement scales are not.

--Shannon

[felix]

Shannon, correct on all accounts. Yes, 22's shoot best. But, is twist the culprit, or is it lower mass, or what? ... felix

[Tiger]

Larry,

Your problem seems to be the formula for getting rpm from the velocity and rifling twist data. You are stuck on time and it's obvious. That formula give you rpm, which we know is revolution per minute. You are not seeing that in 100 yards that the bullet time of flight is in fractions of a second. Let's look at what 45 2.1 said as he said what I was trying to say much better and in more plain terms:

If you want to keep talking about high RPM numbers, bring it into context: 10" twist with Time of flight (TOF) at 100 yds for: 2400 fps = 100 yds x 3 ft/yd / 2400 fps = 0.125 seconds. For 1600 fps TOF = 100 yds x 3 ft/yd / 1600 fps = 0.1875 seconds. RPM (2400 fps) = 2400 x 72 = 172,800 RPM x 0.125 seconds / 60 seconds/min = 360 revolutions. RPM (1600 fps) = 1600 x 72 = 115,200 RPM x 0.1875 seconds / 60 seconds/min = 360 revolutions. All this ignoring external wind and gravity effects to keep it simpler (much like your rounding of RPM numbers).

Take those times of flights (0.1875 and 0.125 seconds) and divide them into a minute (60 seconds) and then take the product of that division and multiply the 360 revolutions by it. You will see that the rpm numbers that appear are identical if you used the rpm formula which is in minutes.
I tried in a wrong way to say that the other day. No matter what velocity you shoot that bullet at to a 100 yard target, it still will only turn 360 times. The only thing that can change that is a difference in time to the target or a change in rifling twist of course.

I am not the judge of people in this thread on rpm but from reading what various people have written a few have a correct understanding of what 45 2.1 is saying. He is right. One person is stuck on writing a book the other too focused on rpm as the damaging factor to high velocity cast bullet acccuracy.

Larry it's not the rpm. One other thing you haven't looked at is that shooting at very high velocity increased the recoil. Take the 30-06 with a twist of 10 and lets use the Lyman 311284 or the Lyman 311299. Both of these bullets are over 200 grains. In order to get them out of Larry Gibson's rpm range on the high side requires what I think is a very high velocity which is going to have much more recoil then a bullet that is lighter and shot within Larry's rpm range for accuracy. I will tell you where I am going with this. None of you here will dispute that a shooter can shoot more accurate with a rifle that doesn't have a lot of recoil. In order to prove Larry's theory a rifle would have to be fixed in a solid firing device that would take all the human error out of the testing.

To just touch on why jacketed bullets are much easier to shoot accurately at high velocity then a cast bullet I say one reason is that they don't exactly duplicate the shape of a jacketed counterpart. I will say that bases on jacketed bullets are more near perfect then a cast bullet's base.
In all my time shooting cast bullets I have never found a plain base bullet that showed melting. I have found many that showed gas cutting. I view gas cutting more of a pressure thing from the gas then of heat. There may be some softening of the bullet alloy near edge corners of the base to help the gas cutting. I think that most the damage that is done to a cast bullet is done inside the bore of the rifle. I have seen cast bullets shot at very high velocity that didn't not leave a smoke trail and they did not disintegrate in flight. I am not claiming that they were very accurate and only make that statement to show they can hold up to a very high velocity.

Ralf

[sundog]

The mass of a jacketed bullet is different at different layers. Obviously. Cast should be the same throughout. So what's there that would cause a problem? You ever watch a top bleed off it's energy? An occasional wobble here or there, sometimes almost not noticed. Difference is that one end is planted firmly on a surface. The axis will return to it's original position and keep spinning, or it could wander to a different spot and then resume straight and level flight, until a enough energy is bled off that it can no longer remain upright. An out of the barrel boolit has no such 'anchor point', but it's time of flight is certainly much shorter than a top.

And what Felix explained earlier about particles further from the axis traveling faster than the particle that is the axis which has no velocity. The speed of the outside of the boolit will change with a change in diameter (if twist and velocity remains the same), or velocity of the boolit (if twist and diameter remains the same), or faster twist (if diameter and velocity remain the same). But in only the latter case is the boolit actually changing the the number of turns or a given distances. Which one is the culprit? Take it easy on me, I'm not an engineer. Of course, in order to get these things to happen, I think pressure has to be adjusted to accomodate the other variables.

[onceabull]

wikipedia= published,the day untold thousands of wannabes are hoping for..... Onceabull

[leftiye]

Tiger et. al The force - centrifugal (I know, you want to use a different word)) comes from the RATE of revolving. The faster the item revolves PER UNIT TIME the greater the centrifugal force. Number of turns accomplished before impact is meaningless, it's HOW FAST (per unit time) the object revolves (active verb). You know how I hate to agree with Larry!

[tube_ee]

Shannon, correct on all accounts. Yes, 22's shoot best. But, is twist the culprit, or is it lower mass, or what? ... felix

Then it would simply be that the imperfections that exist within the bullet are closer to the axis of rotation, and so experience less force, thus disturbing the bullet's flight less than if the bullet was larger.

If we also assume that the "defect density" (defined arbitrarily by me as the number of deviations from perfect uniformity per unit volume of bullet) is constant and also assume that the distribution of defects throughout the bullet is random with respect to position, then as caliber goes up, the "RPM threshold" should go down, as proportionally more defects will be farther away from the axis of rotation.

In other words, if we hold BC (essentially a numerical abstraction of shape, as I understand it) and SD constant (thereby keeping a constant mass/diameter ratio), then as we went from .224 to .308 to .457, the bullets will show reduced accuracy at lower RPMs.

Centripetal acceleration is a quadratic function of angular velocity and a linear function of radius, if the deflection from the bore axis is entirely due to such accelerations, we should see the following proportionalities, with the same assumptions as above:

The deflection will increase as the square of the change in RPM

and

The deflection will increase directly with the change in bullet diameter.

Or, doubling the RPM will cause bullets of the same size to shoot a four times larger group, while doubling the diameter will cause bullets with the same RPM to shoot a two times larger group. Since bullet RPM = twist rate (turns per inch) X velocity (inches per second), you can substitute velocity for RPM directly without changing the proportionality.

Is this true in the real world?

-Shannon

[felix]

Shannon,

True in the abstract! False in the real world. Boolit errors (pre and/or post) are never uniformly distributed. You have to consider a boolit with a comparatively gigantic hole (per caliber) at the radius extremity to make the abstract begin to approach reality. The question always relates to quality control, and somehow an "average" boolit must be obtained for that particular caliber in question. Damn near impossible to decipher what would be "average" across all of our different lead compositions and molding techniques. Air bubbles galore in each boolit is the norm. ... felix

[tube_ee]

and I agree with you, it was just a simplification...

Wouldn't the general trend still hold if the underlying hypothesis is correct?

Even if defects are not randomly distributed, (not evenly distributed, there's a difference), so that there was some mechanism at work that could be correlated to where the voids and/or density variations showed up in the actual bullets, the larger bullets would still have more places for those defects to be where they could have a larger effect.

If, for example, there was a tendency for defects to cluster near the outside edge of the bullet, (like the differential cooling rate might produce... just thinking out loud,) then in that case the smaller bullets would shoot better, because their outside surface is closer to the centerline. Similar logic holds for anywhere you want to cluster the defects along the radial axis of the bullet.

And, to the original point, whether there is such a trend or not, it would seem that there should be some discoverable way of minimizing the absolute defect rate, so that we could shoot our cast bullets at closer to jacketed velocities, which would be the whole point of the exercise anyway.

Is the real question "why can't I shoot cast bullets as fast as jacketed" or "How can I shoot cast bullets as fast as jacketed?" They're not the same question.

--Shannon

[runfiverun]

tube_ee
of course statistically a larger boolit should have more errors [ as any larger sample of anything would]
speed is nnot the only issue here it is speed combined with accuracy, with accuracy being the judge.
the question is ,is the rotational force the limiting factor to accuracy.at higher speed

welcome to the forum join in and have fun.

[KYCaster]

Well, I really should know better, but I'm gonna jump in here anyway.

I can't claim to have any particular expertese in this subject and often have a hard time wrapping my mind around some of the concepts presented here, but generally I can eventually understand what you guys are talking about. One thing I do have is a pretty active BS meter.

I become a bit dismayed when a discussion degenerates into "piling on". For example, the terms centrifugal and centripetal...I have always used the term centrifugal and now that I know that there is a difference, I'm still not sure how each should be used. I would welcome any attempt to educate me when I use the wrong term, but please try not to insult me when you do it. And one more thing...an obvious typo or brain fart should be recognized for what it is. If, in an agitated state of mind, someone types "fps" when "rpm" is obviously the intent then, by all means, call the error to his attention and ask that it be corrected or clarified, but PLEASE, do it politely. Try to keep the demeaning remarks to yourself, they add nothing positive to the discussion and damage the credibility of the person stooping to those tactics.

I admire Larry for taking the initiative to to try to prove (or disprove) a theory that he believes and think he deserves all our support. If you disagree with his methods or his eventual conclusions, by all means pick them apart, we'll all be better off for the knowledge gained, but some of us (I'm sure I'm not the only one) are getting a little weary of the playground tactics.

So, now that I've alienated most of the people involved, a couple of specific points I'd like to address:


Larry,
If you want to keep talking about high RPM numbers, bring it into context: 10" twist with Time of flight (TOF) at 100 yds for: 2400 fps = 100 yds x 3 ft/yd / 2400 fps = 0.125 seconds. For 1600 fps TOF = 100 yds x 3 ft/yd / 1600 fps = 0.1875 seconds. RPM (2400 fps) = 2400 x 72 = 172,800 RPM x 0.125 seconds / 60 seconds/min = 360 revolutions. RPM (1600 fps) = 1600 x 72 = 115,200 RPM x 0.1875 seconds / 60 seconds/min = 360 revolutions. All this ignoring external wind and gravity effects to keep it simpler (much like your rounding of RPM numbers).

Take those times of flights (0.1875 and 0.125 seconds) and divide them into a minute (60 seconds) and then take the product of that division and multiply the 360 revolutions by it. You will see that the rpm numbers that appear are identical if you used the rpm formula which is in minutes.
I tried in a wrong way to say that the other day. No matter what velocity you shoot that bullet at to a 100 yard target, it still will only turn 360 times. The only thing that can change that is a difference in time to the target or a change in rifling twist of course.

Ralf

The RPM numbers that appear are deffinitely NOT identical. The revolutions per distance traveled are identical...that's a constant dictated by the twist rate, but the revolutions per minute vary with the velocity.


And Shannon says:

"Even if defects are not randomly distributed, (not evenly distributed, there's a difference), so that there was some mechanism at work that could be correlated to where the voids and/or density variations showed up in the actual bullets, the larger bullets would still have more places for those defects to be where they could have a larger effect.

If, for example, there was a tendency for defects to cluster near the outside edge of the bullet, (like the differential cooling rate might produce... just thinking out loud,) then in that case the smaller bullets would shoot better, because their outside surface is closer to the centerline. Similar logic holds for anywhere you want to cluster the defects along the radial axis of the bullet."

Cast boolits will always have variable density because cooling and solidification take place from the outside of the mold cavity...heat is conducted away from the alloy through the metal mold block and radiated into the surrounding air...causing the surface of the boolit in contact with the mold block to solidify first and most of the shrinkage to be drawn from the still molten alloy at the center of the boolit. This leaves the center of the boolit less dense than the shell, and in extreme cases will leave a void in the center.

Multi cavity molds will have an effect on the position of the lower density area because the heat loss is not equal around the circumference of the cavity, The mold will always lose heat slower where the cavities are close together thereby causing lower density parallel to the parting line.

Some casting techniques are supposed to reduce this effect, but casting with a single cavity mold would be the only way to reduce the effect to an absolute minimum.

BTW, Shannon, welcome to the cast boolit forum. Despite some of the sniping going on in this thread, the people here are generally well behaved and have the best interests of the casting fraternity in mind. Sometimes a heated discussion is the best way to sort out our differences and reach a conclusion that will help advance the art of boolit casting.

Thanks to all who have contributed to this discussion.

Jerry

[Larry Gibson]

Ralf

Your problem seems to be the formula for getting rpm from the velocity and rifling twist data. You are stuck on time and it's obvious. That formula give you rpm, which we know is revolution per minute. You are not seeing that in 100 yards that the bullet time of flight is in fractions of a second. Let's look at what 45 2.1 said as he said what I was trying to say much better and in more plain terms:

It is not a problem. The tests so far have indicated that. I am not stuck on time. It is RPM, M stands for minute. That IS time. It is in the equation, to take it out is meaningless.

If you want to keep talking about high RPM numbers, bring it into context: 10" twist with Time of flight (TOF) at 100 yds for: 2400 fps = 100 yds x 3 ft/yd / 2400 fps = 0.125 seconds. For 1600 fps TOF = 100 yds x 3 ft/yd / 1600 fps = 0.1875 seconds. RPM (2400 fps) = 2400 x 72 = 172,800 RPM x 0.125 seconds / 60 seconds/min = 360 revolutions. RPM (1600 fps) = 1600 x 72 = 115,200 RPM x 0.1875 seconds / 60 seconds/min = 360 revolutions. All this ignoring external wind and gravity effects to keep it simpler (much like your rounding of RPM numbers).

Take those times of flights (0.1875 and 0.125 seconds) and divide them into a minute (60 seconds) and then take the product of that division and multiply the 360 revolutions by it. You will see that the rpm numbers that appear are identical if you used the rpm formula which is in minutes.
I tried in a wrong way to say that the other day. No matter what velocity you shoot that bullet at to a 100 yard target, it still will only turn 360 times. The only thing that can change that is a difference in time to the target or a change in rifling twist of course.

That is correct; the bullet will turn the same number of revolutions in distance. I have said that before and in this thread. The problem is you are taking out the "time", i.e. the M part of the equation. The faster the bullet travels the distance the higher the RPM. It is that simple and you can figure it anyway you want and it's not going to change.

I am not the judge of people in this thread on rpm but from reading what various people have written a few have a correct understanding of what 45 2.1 is saying. He is right. One person is stuck on writing a book the other too focused on rpm as the damaging factor to high velocity cast bullet acccuracy.

45 2.1 is wrong. I really don't care how you judge me. Judging me does not matter. You need to judge the facts. 45 2.1 has the facts wrong. If you side with his judgement then you are wrong as it is contrary to the facts. I am not "stuck" on anything, the tests are proving RPM is the culprit.

Larry it's not the rpm. One other thing you haven't looked at is that shooting at very high velocity increased the recoil. Take the 30-06 with a twist of 10 and lets use the Lyman 311284 or the Lyman 311299. Both of these bullets are over 200 grains. In order to get them out of Larry Gibson's rpm range on the high side requires what I think is a very high velocity which is going to have much more recoil then a bullet that is lighter and shot within Larry's rpm range for accuracy. I will tell you where I am going with this. None of you here will dispute that a shooter can shoot more accurate with a rifle that doesn't have a lot of recoil. In order to prove Larry's theory a rifle would have to be fixed in a solid firing device that would take all the human error out of the testing.

It is the RPM, the tests are proving it. I can shoot 1/2 MOA goups all day long with 175 gr MKs at 2680 fps out of that M70 .308. That load has more recoil than the 177 gr cast bullet at 2400 fps. So why is recoil not making me shoot bad groups with the 175 gr MK? It doesn't is the answer. You also are grasping at straws along with 45 2.1.

To just touch on why jacketed bullets are much easier to shoot accurately at high velocity then a cast bullet I say one reason is that they don't exactly duplicate the shape of a jacketed counterpart. I will say that bases on jacketed bullets are more near perfect then a cast bullet's base.
In all my time shooting cast bullets I have never found a plain base bullet that showed melting. I have found many that showed gas cutting. I view gas cutting more of a pressure thing from the gas then of heat. There may be some softening of the bullet alloy near edge corners of the base to help the gas cutting. I think that most the damage that is done to a cast bullet is done inside the bore of the rifle. I have seen cast bullets shot at very high velocity that didn't not leave a smoke trail and they did not disintegrate in flight. I am not claiming that they were very accurate and only make that statement to show they can hold up to a very high velocity.

Just what the heck does shape of the bullet have to do with recoil? I suppose you and 45 2.1 will come up with some bastardized way of interpreting the formula on calculating recoil(?). Excuse me but that is just too far fetched for me to waste any more time on.

Larry Gibson

[felix]

I agree, Jerry. Only Larry should call the deal off, and I hope he does not until all of his "facts" are in for us all to see. Yes, I would like to see a practical limit/threshold in RPM be established and I hope we don't have to resort to single banger molds to increase that limit a significant amount. If so, so be it, let's start ordering single bangers. ... felix

If I had any single bangers, I would gladly submit mine to him for use to augment his final statistics with his molds. ... felix

[Larry Gibson]

felix, jerry

I don't think we need to go to just single cavity moulds. Granted single cavity mouldshave been proven to provide the most accurate bullets as they are consistent from the same cavity. However, bear in mind I am not attempting to find the most accurate loadfor each rifle. I am only trying to fnd where accuracy begins to be lost. I m looking at when accuracy begins to get proportionally worse.

Larry Gibson

[Tiger]

Jerry,

You are partially right on voids and shrinkage. There is a good write up about it in the NRA Cast Bullet book. Most common molds of today are bottom pour. The heat does radiate from the molten alloy to the block and then to the surrounding air. A good portion of the heat goes to the sprue puddle and this is where you can see the shrinkage and often a void. This shrinkage area in a bottom pour mold is near an important part of the bullet, the base. The NRA article said they sectioned many bullets and of equally different calibers that were correctly casted and found no voids. That's important to absorb the words correctly casted. They went on to say casting that was not done correctly then found voids. Yes, in the center like you stated. I see that mention of a single cavity mold was brought up but nobody so far mentioned holding the mold sprue plate against the spout of a bottom pour furnace to get a full fill of the mold and helped by the pressure of the molten alloy in the pot. Wouldn't this give you the best possible void free bullet?

Yes the rpm is there where the formula for it says that it is but it becomes again a factor of time. What I mean is that the bullet is in flight such a sort amount of time I do not believe the rpm has much time to work on damaging the bullet in whatever way some think that it is doing.
Just like the hot flame of the powder burn. It is hot enough to melt the bullet alloy but it doesn't have enough time to act on it. You know like when you touch something that is hot very quickly with your finger as oppose to touching it a longer period of time.

I think in the end many are grabbing at excuses. First and still, the rpm. Then the many different descriptions of centrifugal force. Then the composition of the alloy in the bullet and how it solidifies. Paper patching was brought up and nobody is looking there to the reason why they can be shot at high velocity with respectable accuracy.

There are shooters who get accuracy at high velocity with cast bullets and there are shooters who don't. Who can explain that to me?

Larry hang in there and continue with your test. I can say that at least you are trying and doing something to come to a conclusion.

Ralf

[45 2.1]

It is not a problem. The tests so far have indicated that. I am not stuck on time. It is RPM, M stands for minute. That IS time. It is in the equation, to take it out is meaningless.

If you want to keep talking about high RPM numbers, bring it into context: 10" twist with Time of flight (TOF) at 100 yds for: 2400 fps = 100 yds x 3 ft/yd / 2400 fps = 0.125 seconds. For 1600 fps TOF = 100 yds x 3 ft/yd / 1600 fps = 0.1875 seconds. RPM (2400 fps) = 2400 x 72 = 172,800 RPM x 0.125 seconds / 60 seconds/min = 360 revolutions. RPM (1600 fps) = 1600 x 72 = 115,200 RPM x 0.1875 seconds / 60 seconds/min = 360 revolutions. All this ignoring external wind and gravity effects to keep it simpler (much like your rounding of RPM numbers).

Take those times of flights (0.1875 and 0.125 seconds) and divide them into a minute (60 seconds) and then take the product of that division and multiply the 360 revolutions by it. You will see that the rpm numbers that appear are identical if you used the rpm formula which is in minutes.
I tried in a wrong way to say that the other day. No matter what velocity you shoot that bullet at to a 100 yard target, it still will only turn 360 times. The only thing that can change that is a difference in time to the target or a change in rifling twist of course.

That is correct; the bullet will turn the same number of revolutions in distance. I have said that before and in this thread. The problem is you are taking out the "time", i.e. the M part of the equation. The faster the bullet travels the distance the higher the RPM. It is that simple and you can figure it anyway you want and it's not going to change.
So, what your saying is it takes (0.1875 - 0.125) = .0625 seconds less to damage a boolit than what the original 0.1875 seconds didn't? It's traveling faster, so has less time to damage it. Explain it, if you will if time or RPMs is the culprit ..................

I am not the judge of people in this thread on rpm but from reading what various people have written a few have a correct understanding of what 45 2.1 is saying. He is right. One person is stuck on writing a book the other too focused on rpm as the damaging factor to high velocity cast bullet acccuracy.

45 2.1 is wrong. I really don't care how you judge me. Judging me does not matter. You need to judge the facts. 45 2.1 has the facts wrong. If you side with his judgement then you are wrong as it is contrary to the facts. I am not "stuck" on anything, the tests are proving RPM is the culprit.
Just how am I wrong? Since you haven't finished and posted a conclusion, your statement would seem premature. Or is something else going on?

Larry it's not the rpm. One other thing you haven't looked at is that shooting at very high velocity increased the recoil. Take the 30-06 with a twist of 10 and lets use the Lyman 311284 or the Lyman 311299. Both of these bullets are over 200 grains. In order to get them out of Larry Gibson's rpm range on the high side requires what I think is a very high velocity which is going to have much more recoil then a bullet that is lighter and shot within Larry's rpm range for accuracy. I will tell you where I am going with this. None of you here will dispute that a shooter can shoot more accurate with a rifle that doesn't have a lot of recoil. In order to prove Larry's theory a rifle would have to be fixed in a solid firing device that would take all the human error out of the testing.

It is the RPM, the tests are proving it. I can shoot 1/2 MOA goups all day long with 175 gr MKs at 2680 fps out of that M70 .308. That load has more recoil than the 177 gr cast bullet at 2400 fps. So why is recoil not making me shoot bad groups with the 175 gr MK? It doesn't is the answer. You also are grasping at straws along with 45 2.1.
I don't have a horse in that race. I and several others on this board have already been where your trying to go (whether you believe it or not). We all have posted what you need to look at to get there. If your choice is to ignore those posts, fine, but do not call us wrong when you haven't got there. The "I can't do it, you can't either" attitude doesn't work here.

[Tiger]

Larry

Your theory is that when cast bullets are shot above your rpm range that the accuracy won't be as good. The same bullet shot inside your rpm range will be correct? Then tell me why many others on this thread keep posting other ideas of why the bullet isn't accurate above your rpm range. Do good cast bullets magically develop voids when shot above your rpm range?

Ralf

[Larry Gibson]

45 2.1

"So, what your saying is it takes (0.1875 - 0.125) = .0625 seconds less to damage a boolit than what the original 0.1875 seconds didn't? It's traveling faster, so has less time to damage it. Explain it, if you will if time or RPMs is the culprit .................."

I never said the bullets are damaged by RPM. The centrifugal force acts upon the imbalances already in the bullet. Those imbalances are there because of design, casting or were created during acceleration. And yes the time of flight the less the effect the RPM will have. This is why I always say for rifle loads 50 yards is not a good indicator of accuracy. It needs to be 100 yards minimum. The longer the range the greater the effect because the bullet is in flight longer.

"Just how am I wrong?"

So far you are totally ignoring the results of the test so far. Every time I ask you to look at it or refer back to those results you ignore the results, don't answer the question and go off on another accusatory tangent. Look at the results of the test completed so far and post questions regard those results. Abstract theories with no test results do not prove anything.

"I don't have a horse in that race. I and several others on this board have already been where your trying to go (whether you believe it or not). We all have posted what you need to look at to get there. If your choice is to ignore those posts, fine, but do not call us wrong when you haven't got there. The "I can't do it, you can't either" attitude doesn't work here."

Sorry, I forgot to put who that part referred to. You do not seem to understand. I am not trying to go where you have been. You, Bass and other claim good accuracy at high velocity. I have been there too.

What I am trying to prove is the existence of the RPM threshold. How that threshold adversely affects the accuracy of regular cast bullets in rifles. Why certain designs of bullets can only be pushed into or through that threshold so far. And what it actually takes to push through that threshold to attain considerably higher velocity. I am unaware that you have conducted any tests to prove or disprove the RPM threshold. I know you have posted how to push the 6.5 Swede up to 1800 fps or so as we have traded information on that. However those methods and results only prove the existence of the RPM threshold in an indirect way. Are there other tests?

Larry Gibson

[Larry Gibson]

Ralf

Your theory is that when cast bullets are shot above your rpm range that the accuracy won't be as good. The same bullet shot inside your rpm range will be correct?

That is the basic precept.

Then tell me why many others on this thread keep posting other ideas of why the bullet isn't accurate above your rpm range. Do good cast bullets magically develop voids when shot above your rpm range?

The ideas several post are part of what we are looking at. Ideas of others ignore the facts and results of the actual tests. They offer no test results to demonstrate their ideas, only abstract theories. I point out the problem with those abstract theories and use test results or refer to scientific laws. A couple others just present ideas that are off on tangents for what appears to be just argument.

Your preconceived answer to your own question is incorrect. The bullet may have a void, if so then it occurred during casting or prior to the flight of the bullet. As I’ve said before; the RPM affects the imbalanced bullet. The imbalances occur prior to flight. It is during flight where the RPM affects them.

This test is directed at proving and demonstrating the existence of the RPM threshold. Sor far the results of the test are proving that. Questions and comments regarding this test should be relevent and should have factual test results to back them up if contradictory to this test results. Just giving some uproven abstract theory or idea is not the correct way to further meaningful discussion. If anyone has some proof (actually results not just an idea) that the results of the test are incorrect then I certainly want to hear it.

Larry Gibson

[Tiger]

Larry,

I didn't preconceive my answer. I'm throwing things out there to jog your mind which it seems that I have done. We are getting somewhere now that you have basically said that others are just throwing ideas and some for the sake of just to get into the argument. That basically says that just a few know what they are talking about.

According the NRA article in their Cast Bullet book, voids created by shrinkage in the mold are almost always centered. They went on to say that such centered voids didn't upset the bullet balance much. They also said that such voids could be almost totally eliminated by better casting techniques, but casting techniques is a whole other subject.

Here are some more things I will throw out to you. I think the bullet lube, the fouling that gets into the bore, and temperature when shooting are things that have an effect on accuracy not only at low velocity, but more so at higher velocities. When I talk about bore fouling I not only talk about fouling which is very obvious to the naked eye but also what the naked eye can not see. I think that fillers play more of role then just positioning the powder charge. I feel they some how condition or clean the bore, along with sealing gases from getting past the bullet base. We know that in many instances that shooting a large quantity of cast bullets that the accuracy can decline. That is obvious that fouling can destroy the accuracy so any means by which you can prevent or limit the fouling can be beneficial.

What say you Larry?

Ralf

[Larry Gibson]

Ralf

I'd say you got some pretty good ideas there and are tracking. Also, I don't want to give the impression that those who want to argue don't know what they’re talking about. They most often do. They just need to put those ideas in a constructive way and, if contradictory to this tests results, then give evidence by way of tests, either their own or someone else's. They also must understand that the tests they provide must stand up to scrutiny and be relevant to the discussion.

Centered voids can cause problems at higher velocity as we are pushing at higher pressure. The bullet can collapse unevenly into the void unbalancing the bullet. This is just as the bullet can collapse unevenly in the lube grooves.

All the things you discuss are good examples of things that can happen to the bullet. Keep in mind those things happen internally in the barrel. We are measuring the internal ballistics. Hopefully we can catch those anomalies when they appear. They all affect the balance of the bullet. However, again keep in mind; it is the RPM that affects those imbalances during the bullets flight. The imbalances by themselves do not cause the inaccuracy.

Larry Gibson

[felix]

Ralf, voids can only be minimized by casting techniques, never eliminated, and not even close to being eliminated. Heavily swagged wire is the norm for bullet cores to eliminate wire making voids. If there is going to be a jacketing operation in your future, even for paper patch, the boolit being further swaged into shape should come from wire and not from a mold. For proof, take any cast boolit/core and throw it into a polishing gadget. Eventually, you will see the air holes appear all around the object. On a side note, I prefer boolits with shallow rounded grooves. The boolits seem to be tougher with this arrangement, as by measuring the increased spring back they have when compared to those with a large square groove from the same pot of lead containing enough antimony to make it happen like so. ... felix

[leftiye]

Larry, You just walked right through the middle of one of my main problems with this whole process. That being that in your process of sorting out the factors which do or may affect accuracy you are only considering a small portion of the arguments presented. As Tiger said, this reflects a certain lack of respect for those whose ideas you refuse to address. I don't think of it as lack of respect on your part, just a somewhat misguided way of looking at what deserves to be considered.

For example, internal (ballistics) factors that have long been known to cause inaccuracy due to loading techniques (the only thing we reloaders have control over), and what happens during acceleration in the barrel aren't to be given air time because they occurred prior to the boolit leaving the muzzle. Casting defects aren't to be considered because they occurred even before internal factors. Pressure effects at the muzzle, poor crowns, deformed boolit bases at exit from the muzzle are other thangs that don't qualify for some other reason. Paper patched boolits going faster than they're supposed to while still being more accurate than they should be aren't allowed, you only want to deal with plain cast boolits. Several factors that affect accuracy DURING FLIGHT (one possibly vastly more destructive to accuracy than RPMs - bullet deformation from friction in the air, and it will happen at some velocity less than 3300 fps) recieve no comment whatsoever. Calculating ballistic coefficient doesn't adequately cope with boolit deformation in all of its sources, especially when it doesn't compare BC at exit with terminal BC (it only indicates that something was wrong, something that is not necessarily related to deformation).

I have never done anything that resembles a SCIENTIFIC test with regards to any gun related concept. I have no fear whatsoever that my ideas, and principles with regards to reloading are more than minimally faulty. To totally reject ideas proferred (most of which are reloaders theories of long standing, and doubtless correct - it is inconcieveable that were scientific tests were performed that most of these would be found faulty) simply because the writer doesn't support the idea with referrences to scientific findings is a cop out. Sounds mostly like you just don't want to experience the frustration with "them there heretics".

As I've said before, if you only want to study the effects of RPMs on accuracy, this is a worthy study, but you should present it as a study of a narrow, restricted part of cast boolit accuracy, not the whole banana. Virtually everybody here accepts that RPMs have an effect, and that at some rotational speed it will become an unsurmountable obstacle to accuracy, but that's enough said. For my money there's more going on. RPMs isn't THE culprit (to quote you), it's only one of many issues to be overcome.

[Tiger]

Felix

Yes that is true of the voids that one can not see with his naked eyes. You have to admit from some of the excellent targets shot at matches come pretty close to a bullet with no voids. Some say that Electro Type metal doesn't shrink but I read that is a myth because it fills the mold out more sharper then most any other alloy giving it an appearance that it doesn't shrink. Maybe it would be a good metal for casting for high velocity accuracy.


Leftiye

Good post that looks like you are thinking very hard. I would like to know at what velocity friction from the air really starts to melt a cast bullet.

What would be wonderful is if a high speed video could be taken of a cast bullet shot out of Larrys rpm range and out of a fast twist rifling to see what is happening, if and when it starts to wobble.

Some have compared the balance of a cast bullet to that of an automobile tire. We know know what happens when your tire is not in balance. It's a vibration but that is all. Your wheel doesn't fly off your automobile. What would happen if the bullet does vibrate a little from being out of balance?

[leftiye]

Tiger, Thanks for the kind words. Actually, I think Larry has a valid hypothesis, as I said. The situation with nose melt at some high velocity seems unavoidable. It will be an insurmountable problem. I understand that some jacketed bullets are having a similar problem in excess of 4000 fps. One might guess that before that happens the jacketed boolit jacket becomes a container with at least part of the lead being molten (and the rest being very soft - talk about varmint bullet!). Way before the boolit nose deforms visibly, heat will soften the boolit, and RPMs will probly bend it or cause some other deformation that destroys accuracy. I also see this heating of the boolit base by powder flames acting in conjunction with pressure as possibly explaining the fact that plain bases which supposedly don't melt fail at moderate pressures which are not supposed to be high enough to overcome the plastic fail strength of the lead. If these melting/pressure phenomena were to happen at around Larry's RPM (barrier) threshold it WOULD be fun to watch. I suspect that the RPM thang will come first (at lower velocities) though.

[runfiverun]

SPEER 30 CAL [.308] 125GR
"TNT" HOLLOW POINT

these high-energy, thin-jacketed varmint bullets
are designed for total disruption upon contact.
they are especially recommended for the 308, 30.06
and other dartridges in this velocity class. they
give maximum accuracy at these velocities.

NOT RECOMMENDED fo use in rifles having
twists quicker than 1 turn in 10 inches. DO not
exceed velocities of 3100 feet per second.




hmmmmm..............somebody want to give speer a call ???

less than 3100 fps nor faster than 1 in 10
wonder how they come up with this.

[Larry Gibson]

Leftiye

Let me try this one more time.

“you should present it as a study of a narrow, restricted part of cast boolit accuracy, not the whole banana”

That is exactly what I am doing. It is you and a couple others that do not see that. Please go back and read Chapter 1. It explains it. I am not “sorting out the factors which do or may affect accuracy you are only considering a small portion of the arguments presented”. Those “factors” are factored in so I can focus on the specific aspect of how RPM affects the cast bullet.

Once again I shall explain it; I am not trying to develop the most accurate load for any of the rifles. Is that plain enough? I do not need to develop the most accurate load. If the rifles shoot 1.5 - 2 moa in or below the RPM threshold and 3 -7 moa above the RPM threshold (depending on the twist) with the loads I am using that proves the same point as if I go to all the trouble to find the most accurate load for each rifle and they still shoot 3-7 moa above the RPM threshold. The result is the same; the accuracy decreases above the RPM threshold. Is that so hard to understand that we do not need the “most accurate load” to find out what we need to know. By using a proportional comparison of the accuracy of each rifle to the proportional accuracy of the other rifles the results are the same. Even if I fine tuned the load and all three rifles shoot 1 moa or less and if they shoot 2-3 moa above the RPM threshold at the same velocity the result is the same. If the 10” twist shoots proportionally larger than the 12 and 14” and the 12” shoots proportionally larger than the 14” twist all at the same velocity then the result is the same. That result is that RPM is the culprit.

I am casting good bullets with a good alloy and visually culling those with obvious defects like voids in the base, voids anywhere else, with non filled out spots and bad bases. The GCs are Hornady’s and are pre-seated with the Lyman 450 before sizing at .309 and lubing. I am using cases that are matched prepped and fire formed to the rifle. They are neck sized in bench rest dies. I am using new H4895 and other powders. The primers are Winchesters. The lube is Javelina, a very proven lube. The rifles are all moa or capable of sub moa. They do not have bad crowns or bad bores. They shoot very well with both cast and jacketed bullets.

Actually all three rifles shoot the 311291 bullets quite accurately. If there were any of the consternated over problems you and some are having they would not shoot them well at all. Would they? That is why “other thangs that don't qualify for some other reason” because they are not applicable.

The point is; those three rifles all shoot those bullets well in the RPM threshold. All three rifles begin to lose accuracy above the RPM threshold. The 10” twist loses proportionately more than the 12” and the 14”. The 12” loses proportionately more than the 14”. Pressures are the same, velocities are the same, and the only thing different is the RPM and accuracy. So guess what?

First you chastise me and my test for this; “you should present it as a study of a narrow, restricted part of cast boolit accuracy, not the whole banana”, then you chastise me and my test for this; “Paper patched boolits going faster than they're supposed to while still being more accurate than they should be aren't allowed, you only want to deal with plain cast boolits.” You don’t even know which way you want it…..

Now if any of you feel slighted I perceive is not because I “reflects a certain lack of respect for those whose ideas you refuse to address”! It is I who should feel slighted because you and some others all show a lack of respect for me by not reading what I write. I continually have to tell you and others over and over again what I am doing and why I am doing it and to look at the test results. You and others continue to ignore the obvious. If you feel that is a “somewhat misguided way of looking at what deserves to be considered” then feel free to conduct your own test and report back the results. I’d be more than happy to see your results.

Conceive or proffer what you will, when those “reloaders theories of long standing, and doubtless correct” are contrary to test results and those who proffered them do not provide test results to prove their theories then I probably will continue to “cop out” and not support the unproven or untested theories of “them there heretics.”

I just got to your last paragraph and I’m wondering why I’m wasting my time on someone who agrees then disagrees in the same paragraph.

Larry Gibson

[Bass Ackward]

Good discussion. Glad other folks are joining in.

Talking with another local fella here. He said assuming perfect bullet flight, air flow from the right or left could make a bullet either rise or drop depending on the direction of the wind and the direction of the rotation. (Right or left hand twist) He said that the steeper the angle marks on that bullet, the greater the diverting effect.

Which translates out to the faster the twist, the greater the movement will be with the same wind. Obviously, bullet speed when thought of in MPH makes it easier to understand that as velocity increases, the negative effect increases too. Much like changing the pitch on a proper blade. This would definitely support the results seen with the RPM theory, as Larry says that even when things are done right, best accuracy is always down low. Just not necessarily from an outta balance standpoint that he is focused on. Especially when one considers the negative that grease grooves play in the BC equation, this effect would be amplified on cast bullets compared to jackets.

So separating these things out to a single factor is not easy. It might be that each has a stronger effect at different points on the scale. The scale being defined by cartridge volume, barrel length, and bore diameter and the twist rate required by that bore diameter. Which is why I suspect the people that came before us adopted the generalities to 1. use the slowest twist required to stabilize, 2. use the longest barrel possible, and 3. use the best ballistic coefficient bullet for longer range use. (a lighter per caliber bullet would have less grease grooves than a heavy bullet too.)

All three of these things play an inseparable part in the final objective which is accuracy limited by the gun and the reloaders understanding of what is required for more. Are there more factors?

[felix]

Yep, baseball was my first love. Well, that sorta' petered out over the years after all the ******** and moaning. Nothing but a bunch of sissy movie stars anymore, with the same mental attributes, at least starting down that road. ... felix

[Larry Gibson]

Bass

Those are good points and they and any more we come up with are certainly part of a final object of accuracy. Air flow based on bullet rotation does cause the bullet to divert; we refer to it as drift. However it is a long range phenomena with little measurable effect at the close range of 100 yards. What effect there might be from drift causes the bullets to move in the same direction and results in a POI shift of the group. It does not result in dispersion of the group as the effect is the same on each bullet fired.

Again let me remind everyone; I am not seeking the most accurate load. I am only isolating those factors which cause inaccuracy at higher velocity. The initial objective is to determine the existence or not of the RPM threshold. If in the latter portion of this test I isolate a factor that improves accuracy at high velocity that will be enough. I will not attempt to determine just how much of that factor gives the ultimate accuracy. That right now is beyond the scope of what I am doing. I. E. if I find harder alloy tightens the group I will not proceed to find out which hardness tightens the group the most. It is not pertinent to this test “how much” but only “if it does”.

If anyone cares to take what we find here using actual tests to isolate those accuracy factors and adapt it to their loads to find the most accurate loads for their rifles at high velocity they are more than welcome. We will have accomplished something by furthering our knowledge with facts. If they take what we find here and decide they can’t get to high velocity with the cast bullet/loads they’re using and want to pursue a custom bullet such as your LBT then we’ve accomplished something.

Larry Gibson

BTW; I am not 'focused" on "outta balance" bullets. All bullets are "outta balance". All bullets, cast and jacketed, when fired are "outta balance". It is why we shoot groups instead of all shots into one hole. What I am focused on is why cast bullets only shoot well to a certain point at medium velocity. I am focused on why there is a threshold that is difficult (I did not say it can't be done) to get through to have equal accuracy at high velocity. The evidence points to RPM as the reason. If we are going to shoot with equal accuracy at high velocity/RPM with cast bullets then what are the things we can do to negate the adverse effects of that RPM.

[Tiger]

First I would like to address Runfiveruns post on the Speer 125 grain TNT in 30 caliber. I went to Speer website and could find nothing like what he said about it. Why would he make a comment that the bullet is especially designed for the 308 and 30-06 and in the next sentence say "not for use in rifles with a 10 twist"? I know of very few 30-06's that have a slower twist then 10.

Larry,

I must be talking Greek. Pretty much what Bass said about the bullet turning left or right depending on the barrel twist direction, is pretty much what I was trying to tell you about the golf ball spin. You accept his theory and throw mine out like I am crazy or something, when I very them as much alike.

Felix,

Baseball....amazing. With a first name of Felix you would have been a very famous baseball player.


Ralf

[runfiverun]

i did not say it i copied it directly as written on the tag that was in the box
of bullets.
speer 30 cal 125gr
.308 hollow point "TNT" part #1986

was pointing out here that even jacketed bullets have velocity and more

important to the discussion here rpm limitations placed upon them
by a credited manufacturer

[Tiger]

i did not say it i copied it directly as written on the tag that was in the box
of bullets.
speer 30 cal 125gr
.308 hollow point "TNT" part #1986

was pointing out here that even jacketed bullets have velocity and more

important to the discussion here rpm limitations placed upon them
by a credited manufacturer

Hardly likely runfiverun....it's not the rpm...it's the velocity. Let us take a look at the 220 Swift. It's very famous for vaporizing light bullets. The normal twist on them is 14. Let us examine the rpm at 4100 fps. I get 210857.14 rpm. Now let us look at the many 1 in 7 twist AR15's that are on the market. Take a velocity of 3100 fps and that gives us 318857.14 rpm...and I don't know anyone vaporizing bullets with that rifle and twist.

Do you want to try again?

Ask an aviation engineer how hot the skin temperature get on the newer fighter jets of today. I would say that those planes don't spin...wouldn't you?

Ralf

[runfiverun]

don't need to try i posted as written.
i also do not work for speer.
i have heard of [dont own an ar-15] from credible sources
abot these rifles producing the grey puff. i have however seen first hand
the 220 produce the grey streak.
and have experienced the shot gun affect of a higher velocity load
where all is good by just reducing the powder.
was it the velocity or was it the twist. well it didn't just throw them all lower
or higher or all of them to the right.

they were all over the place. that 100 fps sure made a difference.

just my observations, sure wish i had a camera to show this tag and box.

as far as the temp thing are you saying that the velocity caused a jacketed
bullet to get hot enough to melt and then explode?

i would think it would cause set back of the nose and then be thrown apart by rotation

[Tiger]

runfiverun

Tell me how then you can take the same bullet and shoot it in a 220 Swift and vaporize it and then shoot the same bullet in any barrel with a 7 twist for almost 100,000 more rpm and not vaporize it, if it's the rpm that destroys. No need to reply if you say it's not the rpm.

I did not say I did not believe you about the tag that comes inside Speers bullet box with the bullets you mentioned. I am just saying I went to their website and they said nothing about it. I just thought that was strange.

Ralf

[w30wcf]

Tiger,
As I recall, it was the deeper rifling on some of those .220 Swift barrels that cut deeper into the bullet jacket, thus weakening it, leading to bullet failure in flight.

w30wcf

[runfiverun]

what im saying here is that any problems, inherent or otherwise
are, completely finished, by rpm's
rpm's cause their own problems
we have seen with bass's test that if you harden the out-side of a bullet any bullet
that things seem to stay together better.
but at what point does accuracy suffer?

if i could shoot a 180 grain bullet at 4000 fps and have it expand
and cause an exit wound, guess what i would shoot.
something has to be causing a bullet all bullets to fail accuracy wise
and somehow it seems to be tied to velocity which
to me also seems to be tied to rps.

you are causing somehow somewhere damage and it is being done in by rpm's on
it's way to the target.

my take on it

[Bass Ackward]

BTW; I am not 'focused" on "outta balance" bullets. All bullets are "outta balance". All bullets, cast and jacketed, when fired are "outta balance". It is why we shoot groups instead of all shots into one hole.


Well, if you want more stuff to blow your mind. I have re-chambered air gauged barrels from one caliber to another and had accuracy improvement or degradation. I use the term air gauged so that we realize these barrels are supposed to be of the highest quality.

Took a 308 Win that was at best a 1 1/2" gun. Re-chambered it (modified the action too) into a 308 Norma Magnum and it became a solid 1/2".

Took a 220 Swift that was terrible at about 1 1/2" with everything at Swift velocities, cut off 2" and re-chambered it to 223 Rem (this is my current gun) and it is a solid 1/2" with everything now and sometimes a little better than that.

These are two examples of what friction and barrel oscillation can do turning what is thought to be a bad barrel into a good barrel by going both ways on the pressure spectrum.

With cast we cut friction significantly. We also tend to use smaller case capacities. I have broached this before about how bedding can alter barrel vibration enough to change the pattern to achieve better accuracy. At the low velocity area, (RPM zone) vibration is relatively insignificant. But this does get magnified as we go on up in pressure.

Took a Heavy barreled 244 Remington (factory outfit) up to a 240 Gibbs and shot 100 grain bullets over 4000 fps into 1/2" out of a 12 twist.

All I am telling you here is that a barrel can be thought to be good or poor that can really simply need a different oscillation pattern to really change.

Slowing twist rate would cut rotational friction that would minimize barrel vibration which would also look like RPMs.

[Tiger]

Tiger,
As I recall, it was the deeper rifling on some of those .220 Swift barrels that cut deeper into the bullet jacket, thus weakening it, leading to bullet failure in flight.

w30wcf

As will the ones with shallower rifling along with the 22-250. Both of these will smoke the lighter weight bullets. Are you saying that none of the normal rifled Swifts didn't smoke bullets?

Ever look down the bore or 22 caliber barrel with a 7 twist? Looks almost like threading. That can not be healthy to a bullet jacket and yet it is very hard to smoke a light weigh bullet in a 223.

Ralf

[Larry Gibson]

First I would like to address Runfiveruns post on the Speer 125 grain TNT in 30 caliber. I went to Speer website and could find nothing like what he said about it. Why would he make a comment that the bullet is especially designed for the 308 and 30-06 and in the next sentence say "not for use in rifles with a 10 twist"? I know of very few 30-06's that have a slower twist then 10.

Larry,

I must be talking Greek. Pretty much what Bass said about the bullet turning left or right depending on the barrel twist direction, is pretty much what I was trying to tell you about the golf ball spin. You accept his theory and throw mine out like I am crazy or something, when I very them as much alike.

Felix,

Baseball....amazing. With a first name of Felix you would have been a very famous baseball player.


Ralf

They are both drift, I didn't trow yours out at all. Bullet drift happens at very long ranges and mostly in the latter stages of the trajectory. I deferred to you on what happens with golf balls.

Larry Gibson

[Larry Gibson]

Hardly likely runfiverun....it's not the rpm...it's the velocity. Let us take a look at the 220 Swift. It's very famous for vaporizing light bullets. The normal twist on them is 14. Let us examine the rpm at 4100 fps. I get 210857.14 rpm. Now let us look at the many 1 in 7 twist AR15's that are on the market. Take a velocity of 3100 fps and that gives us 318857.14 rpm...and I don't know anyone vaporizing bullets with that rifle and twist.

Do you want to try again?

Ask an aviation engineer how hot the skin temperature get on the newer fighter jets of today. I would say that those planes don't spin...wouldn't you?

Ralf


You might open a box of Hornady .224 SXs. They say pretty much the same limiting the bullets to a certain velocity based on a 14" twist. Shoot them in a faster twist and they spin apart. Same thing with Sierra Blitz's. It's the RPM.

ARs with 7" twists spin the SXs and Blitz's apart t much lower velocities than 3100 fps. Been there done that. Many 9 and 10" twists spin those bullets apart at less than 3100 fps.

BTW; planes don't spin but the fly one hell of a longer than bullets do. How long does it take to heat up the skin temperature compared to the time of a bullets flight?

Larry Gibson.

[Larry Gibson]

runfiverun

Tell me how then you can take the same bullet and shoot it in a 220 Swift and vaporize it and then shoot the same bullet in any barrel with a 7 twist for almost 100,000 more rpm and not vaporize it, if it's the rpm that destroys. No need to reply if you say it's not the rpm.

I did not say I did not believe you about the tag that comes inside Speers bullet box with the bullets you mentioned. I am just saying I went to their website and they said nothing about it. I just thought that was strange.

Ralf

I wonder if you have actually done this? I have, with both cartridges. A heavily constructed bullet that does not spin apart in the .220 will not spin apart in the AR. Conversly the lightly constructed SX, blitz's and some HPs will spin apart in both.

Larry Gibson

[Larry Gibson]

Bass

So what does all that have to do with what I am doing? I don't have any qualms with most of it as I've seen the same things. I've also seen just the opposite.

I am wondering about;

"Slowing twist rate would cut rotational friction that would minimize barrel vibration which would also look like RPMs."

I still haven't seen any test evidence that "rotational friction" is fact. I have seen quite a bit to the contrary though. Also remember I am measuring the porportional change in accuracy between the 3 twists. This factors in any "rotational friction", if there is any, into the comparison. The evidence so far still clearly points to RPM. Remember; same pressure, same velocity, (both of which evens out any difference in "rotational friction") much larger proportional change in accuracy with the 10" twist vs the 12 and 14" twist. The 12" twist also has a proportionally lager change in accuracy than the 14" twist. The only difference between them is RPM. Regardless of the straws we try to grasp the evidence so far is pointing in one direction only, RPM.

Larry Gibson

[tube_ee]

To design an experiment to determine wheter we are looking at an RPM effect, a barrel oscillation effect, both, or both and a bunch of other stuff.

Take a cast bullet load at a velocity and in a rifle where it is shooting poorly.

Change the barrel harmonics. This is not hard to do. Add weight, clamp something around it, slide a thin foam between barrel and stock, whatever. Anything that changes the resonant properties of the barrel changes the harmonic structure of its vibrations.

At this point, we're not looking for improvement, just change. If the increased barrel vibrations induced by higher bullet speed (basic physics there, it's happening) are influencing group size, the group size should change.

As I have read this thread, and thought about what everyone has said and done, I think that Larry and Bass are probably both right. Which makes sense... any time you try to explain a complex dynamic process in terms of one variable, you will be wrong.

--Shannon

[Larry Gibson]

Shannon

I guess we shall see because if you read Chapter 1 you'll recall that changing the harmonics of the barrel via pressure as Bass suggests will be part of the test.

Larry Gibson

[Bass Ackward]

"Slowing twist rate would cut rotational friction that would minimize barrel vibration which would also look like RPMs."

I still haven't seen any test evidence that "rotational friction" is fact. I have seen quite a bit to the contrary though. Larry Gibson


Larry,

Well, you can see evidence of this all around you if you look for it. My data showed you a load that was 5 " at 50 degrees and then 1" over 80 degrees. Same everything. Just less lube as it is used up by temperature. Pressure cure there is exactly the same by your definition, so it has to be maintaining center position better or worse.

Find a muzzle loader for lead some day. How tall is the rifling? Bet it isn't .004. Be more like .015 to .025. I don't have one any more to check. If everyone started with black, this would be ingrained what lowering rifling height does.

Ever go to a gun show? Ever watch the guys looking for the military rifles get down on there knees and pray to God before they remove the bolt to see that it has good rifling in it? Why have rifling height if maintaining it wasn't an issue? Which leads me to the question of what works best for micro groove rifling? Soft or hard? Why? 12 lands X .002 rifling is .024 of drive area. 6 lands of .004 tall rifling is .024 of drive area. Should have the same effect if not for sizing from fouling. IF micro groove rifling were made in 10 twist, you couldn't shoot ANY HARDNESS of lead in "the ideal RPM zone" without cleaning between shots.

Look where the ideal RPM range is for 45 caliber. 1100- 1300 fps even though RPMS aren't a factor here. But they are!!! .004 tall rifling represents a lower percentage of bullet diameter so that it has a lower ceiling. 30s work to 1600 to 1800 because of twist rate and common rifling height. The 22 caliber has .004 tall rifling too. Where is the RPM range for that caliber? Higher right? Why? Because .004 represents the greatest percentage in relationship to bullet diameter. Did the bell go ding?

Remember, I have taller rifling barrels. But the taller rifling can work against you if the leade is too steep. That will cause an even greater shot start initialization pressure that will ruin the bullet that way. With taller rifling, you need a more gentle slope. But if your 10 twist had .006 or .007 tall rifling, the performance of it would improve much closer to your 14 and may beat it. DO you have access to a 30 caliber with poor rifling height to compare?

Look. You are progressing from a single premise here. The theory of slinging bad lead is better with a slower twist. Apparently you are correct. But you should not assume that with hard enough lead for all barrels that the 14 twist barrel will be more accurate than the 10 twist when both are loaded to the same RPMs. Or any RPMS. The 10 may still be superior. Only that the slow twist won't be as wild if you screw up. This destruction occurs IN THE BORE and is agrivated by PRESSURE!

What you are really doing is proving that jacketed height rifling is inadequate for softer lead so that the slower twist outperforms when it let's go. That has been your test so far, since you failed to match hardness to pressure .... or rifling height of your guns.

[Larry Gibson]

Bass

There you go, looking for that "most accurate load" again. Not what I'm testing. Regards your 50/80 degree groups. You say everything is the same so it can't be RPMs. But several things aren't. Simple things like the temperature and the bedding. Since I've also shot that bullet quite well at 50 degrees in my '06 without barrel pressure - with a free floated barrel I's say your problem was a bad barrel that doesn't shoot well when it is cold. Ever think of that?

Mt "theory" is being born out by evidence of tests. I am not sling "bad lead" either. They are good 311291s. 'Tis you that continually come up with different theories without actual tests to support them. You just then just skiop on to a knew theory when one is disproven.

"What you are really doing is proving that jacketed height rifling is inadequate for softer lead so that the slower twist outperforms when it let's go."

You could be right but that is a pretty bold statement considering many discuss the "stripping" of bullets or "letting go" as you call it. However have we actually seen any cast bullets wherre the rifling has been stripped? I haven' in many, many years of looking at them. I am going to hold you to this statement and not let you ignore it like many other claims if thelinotype 311291s exhibit the same type of proportional in accuracy as with the #2 alloy 311291s.

Larry Gibson

[Bass Ackward]

Bass

There you go, looking for that "most accurate load" again. Not what I'm testing. Regards your 50/80 degree groups. You say everything is the same so it can't be RPMs. But several things aren't. Simple things like the temperature and the bedding. Since I've also shot that bullet quite well at 50 degrees in my '06 without barrel pressure - with a free floated barrel I's say your problem was a bad barrel that doesn't shoot well when it is cold. Ever think of that?

Mt "theory" is being born out by evidence of tests. I am not sling "bad lead" either. They are good 311291s. 'Tis you that continually come up with different theories without actual tests to support them. You just then just skiop on to a knew theory when one is disproven.

"What you are really doing is proving that jacketed height rifling is inadequate for softer lead so that the slower twist outperforms when it let's go."

You could be right but that is a pretty bold statement considering many discuss the "stripping" of bullets or "letting go" as you call it. However have we actually seen any cast bullets wherre the rifling has been stripped? I haven' in many, many years of looking at them. I am going to hold you to this statement and not let you ignore it like many other claims if thelinotype 311291s exhibit the same type of proportional in accuracy as with the #2 alloy 311291s.

Larry Gibson

Larry,

I added some more about bore diameters in relationship to RPMS if you will read that last post again. Gotta be short, leaving for Chicago for a couple of days and won't be able to respond. Hope this gives you something to think about.

Don't think you are launching bad bullets? PRove it! Water drop or oven HT some and repeat and see if the they all don't improve. That's easy.

[Larry Gibson]

Bass

Hello........Linotype....hello..........

"Don't think you are launching bad bullets? PRove it! Water drop or oven HT some and repeat and see if the they all don't improve. That's easy"

You just don't seem to understand...I am not looking to get the best and most acurate load. I am testing to determine if RPM is causing inaccuracy. Please grab a clue.

Talk with you when you get back. Enjoy the trip.

Larry Gibson

[Tiger]

Larry

You said: The evidence so far still clearly points to RPM. Remember; same pressure, same velocity, (both of which evens out any difference in "rotational friction") much larger proportional change in accuracy with the 10" twist vs the 12 and 14" twist. The 12" twist also has a proportionally lager change in accuracy than the 14" twist. The only difference between them is RPM. Regardless of the straws we try to grasp the evidence so far is pointing in one direction only, RPM.


To that I say that this is what you say, not all of us. You are the great Albert Einstein, everyone has to prove him wrong. Is this a plan of yours having other find the real reason why there is a difference between rifling twists at higher rpm/velocity?

Yes I have shot the many different bullets out of the faster 22 bores. If I didn't have the rifle I was fortunate enough to have friends that did. We did not come to the same conclusion as have you. What I have found about the tags in bullet boxes is that most have a velocity limitation not a rifling twist limitation. Before you reply to that let me say that does not include the twist limitation because of the heavy weight for bore such as the newer 22 caliber bullets that require the 7, 8, and 9 rifling twists. That is why I found runfiverun's post interesting.

I have thought about Bass's deep rifling twist ideas. I have gone back through old post material and one that caught my attention was when there was much posting about the M95 Steyr 8x56R. It was mentioned in those old post about how deep the rifling is in that rifle. As I recall some of the members were were getting very decent shooting with this caliber and Bass mentioned the deeper rifling in that caliber. I like to agree with him in that area.

Ralf

[leftiye]

Bass, The bell isn't allowed to go ding (broked?). Tiger " You are the great Albert Einstein, everyone has to prove him wrong." Can't be done, not allowed.

[Tiger]

Larry

I make a statement and like a politician you attack it or misconstrue it into something else. I was pointing out with the jet plane that air creates friction which in turn creates heats, lots of it. Just one attempt at saying rpm isn't the animal responsible for jacketed bullet destruction at exceptionally high velocities. It's also not totally a thin bullet jacket either. Many times it can be if the jacket alloy is tough enough to with stand the rifling stresses put on it alone the friction through the air.

That brings up the golf ball again. You just keep on repeating what you have to say about the spin. Let's try this. If you touch a spinning gyroscope what happens? Does nothing happen? I think not. Air does have mass. The centrifugal force of the bullet spinning does have a reaction against the air it is cutting through. What happens to a bullet when it's cutting through animal flesh? Besides the mushrooming or other physical destruction? In many cases it tumbles. Why?

I believe I'm with Bass and others here that most the inaccuracy damage i done to the bullet while still in the barrel.

Ralf

[mainiac]

Havent been on this site very much lately, but am now reading this thread with intrest. If you read back in the history,you will find a thread about my 22 hornet. Up to 2900 with fair accuracy(2600 very accurate) with ACWW. Shoot lyno boolits in this gun and it shoots 15 inch groups,at best!!! Seems boolit hardness aint the answer.BTW, boolit was the 225415 checked,with felix lube. And on to my current head scratcher,,,,,,,,,,,, snows finally melting away up here in the north, today i was shooting and noticed the lead on the ground from my swinging gong target. Have wondered this before,, 70-75% of the lead is ALWAYS spattered off to the left side of the target. It isnt a angle thing,im sure. This has to be a twist thing! Almost all barrells are rifled right hand, and im thinking the direction of the twist makes the boolits shatter left. If I could only get ahold of a left twisted barrell, I would find out! Anybody have any thoughts?

[Tiger]

Havent been on this site very much lately, but am now reading this thread with intrest. If you read back in the history,you will find a thread about my 22 hornet. Up to 2900 with fair accuracy(2600 very accurate) with ACWW. Shoot lyno boolits in this gun and it shoots 15 inch groups,at best!!! Seems boolit hardness aint the answer.BTW, boolit was the 225415 checked,with felix lube. And on to my current head scratcher,,,,,,,,,,,, snows finally melting away up here in the north, today i was shooting and noticed the lead on the ground from my swinging gong target. Have wondered this before,, 70-75% of the lead is ALWAYS spattered off to the left side of the target. It isnt a angle thing,im sure. This has to be a twist thing! Almost all barrells are rifled right hand, and im thinking the direction of the twist makes the boolits shatter left. If I could only get ahold of a left twisted barrell, I would find out! Anybody have any thoughts?

Mainiac

That's good shooting with lead for a 22 Hornet. I will try to explain this before Larry Gibson runs it down. Most Hornets have a rifling twist of 16.
So with that piece of data plugged into the rpm formula along with the 2900 fps, Larry will say that the resulting 130,500 rpm is well within his rpm range limits.

I too have found that linotype doesn't always solve a cast bullet problem but presents more. Notice I said doesn't always. The other times it performed well.

Ralf

[leftiye]

Manic 1, Sometimes the boolit fit isn't quite right, and the boolit has to obturate (get KITA like a muzzleloader boolit does when it bumps up to groove diameter). Sometimes softer lead will continue to do this as it travels down the barrel, and makes up for barrel irregularities or roughness, and damage to the boolit. A hard boolit can't do that. Is it possible that the lino boolit was undersized? Your post on the Hornet warms my heart. I am working on getting one or more Hornets going right now and it helps me to hope for good results.

[Pat I.]

Larry, since the attacks are getting personal and the opposing ideas and helpful hints are a little strange at times why don't you just finish your tests and post or publish the results. That way people can make up their own mind if they believe cast bullets are twist limited for attaining best accuracy. Personally I believe they are but that's unimportant to the conversation or you're testing.

[sundog]

Larry, I did not read back through all the posts in this thread. I did want to convey some info to you though. At the behest of my good buddy, Felix, I loaded some AC WW/RS 314299, sized .312, over 28 and 30 surp 4895 for a heavy bbl .308. That samest batch of boolits shoot extremely well in a custom Mdl 70 with 10 twist. The 28 gr load shot lights out in a heavy wind quartering from the right front, wind NE, shooting N. At 100 yds 9 rounds took out the Xring and the 10th was a very solid 10 at 5 o'clock which was more my fault than anything.

The next 10 rounds were the 30/4895, same boolits, and they made a 4 inch wide group across the top of the black (SR21) with a single round an 8 at 8 o'clock, which again, I suspect was my doing.

So, from 28 to 30, something happened. It wasn't me (I've been shooting long enough to know), and it wasn't the conditions. No chrono. I suspect the 28 grain load at about 1800 - sure was a pretty target.

I shot from this same batch of boolits for the mil bolt match. I shot smallest group of the day with 03A3 @ 1.999 and came in second overall score with a 288/300 and Xs. Did I mention that it was windy? At least 15 G 30 @ 315 (NE) shooting 360 (N). And it was about 40dF at shoot time.

So, what do we suppose about those loads in the .308 with a 12 twist?

[Larry Gibson]

Mainiac

That's good shooting with lead for a 22 Hornet. I will try to explain this before Larry Gibson runs it down. Most Hornets have a rifling twist of 16.
So with that piece of data plugged into the rpm formula along with the 2900 fps, Larry will say that the resulting 130,500 rpm is well within his rpm range limits.

I too have found that linotype doesn't always solve a cast bullet problem but presents more. Notice I said doesn't always. The other times it performed well.

Ralf

Thanks Ralf, you're all over it.

Larry Gibson

[Larry Gibson]

Larry, since the attacks are getting personal and the opposing ideas and helpful hints are a little strange at times why don't you just finish your tests and post or publish the results. That way people can make up their own mind if they believe cast bullets are twist limited for attaining best accuracy. Personally I believe they are but that's unimportant to the conversation or you're testing.

Pat

Like I said; I don't know why I'm still in this converstation. On to the tests. Thanks.

Larry Gibson

[Larry Gibson]

So, what do we suppose about those loads in the .308 with a 12 twist?

ACWWs is a pretty soft alloy these days. Without knowing the velocity I'd say you were in the low end of the RPM threshold with the 30 gr load of 4895. The 28 gr load was accurate, the 30 gr load was not. The 28 gr load was slightly in or below the RPM threshold. The 30 gr load probably exceeded the RPM threshold for that bullet of that alloy in that twist. Would be nice if you would use a chronograph when testing loads as there could in fact be other reasons for the inaccuracy also. Note the example of the inconsistant ignition with the 14" twist during the test I ran. Hard to say exactly without facts. The chronograph would have given us some facts.

Larry Gibson

[Tiger]

ACWWs is a pretty soft alloy these days. Without knowing the velocity I'd say you were in the low end of the RPM threshold with the 30 gr load of 4895. The 28 gr load was accurate, the 30 gr load was not. The 28 gr load was slightly in or below the RPM threshold. The 30 gr load probably exceeded the RPM threshold for that bullet of that alloy in that twist. Would be nice if you would use a chronograph when testing loads as there could in fact be other reasons for the inaccuracy also. Note the example of the inconsistant ignition with the 14" twist during the test I ran. Hard to say exactly without facts. The chronograph would have given us some facts.

Larry Gibson

Larry,

What do you think the velocity, a guess, is of Sundogs 30 grain load? I looked in the Lyman Cast book and they didn't list that exact bullet but the heaviest one listed using a 311334 and a paper patch bullet 301620 did have 4895 loads. First bullet gave 1879 fps to 2497 fps with 28.3 grainds to 40.8 and the second bullet gave 1673 fps to 2427 fps with 23.8 to 38.4 grains of 4895. So to hazard a guess being Sundog is using a faster twist and heavier bullet making his bullet slower then what is listed here, I'd say his 30 grain load was going not much over 1900 fps. If so that gives us 136800 rpm. I do not consider this such a high rpm. Please don't tell me for his alloy, bullet, load, rifling, etc., that this was the limit. With a change in velocity there is a change in many other things, barrel harmonics to name one. Out of hundreds of variables you for some reason selected rpm. I and others disagree. How will your test prove 100 percent that rpm is the accuracy killer?

Ralf

[runfiverun]

with the 30 gr load he was also at about 32000 psi.

[Tiger]

Run

I'm glad that you brought that up. I was just going to post about using different burn rate powders. Say you take four suitable powders with different burn rates and keep assembling and shooting loads until you get loads with all four powders that read the exact same velocity on your chronograph. Ok, my question to all of you is WILL THE ACCURACY BE THE SAME FOR ALL FOUR POWDER LOADINGS? If you say no then that leaves rpm out of the story.

Ralf

[runfiverun]

tiger my first reaction here was no
but ,
if those powders were i4895 h4895 aa2498 i would say yep
if they were 322, 4895 rl-19, h1000
i would say i don't know .

i know what you are saying here internally every thing has more to do
with accuracy.
but whats happening in the bbl is affected by rpm's, as well as what happens
out side of it.

rpm works on the boolit longer than the internals do.
if you were going to build a rifle and was going to use it for cast shooting
would you want the one that is the easiest on it?

i dont see how assembling loads to a certain velocity would leave the rpms out of
the equation.

oh and this is how i start a lot of my load development,anyway.
guess thats why i use 322 in one gun and 4895 in another.
i targeted velocity then worked it around till i was happy with it.

[Larry Gibson]

Ralf

Sundog did not say whether his rifle was a 10 or 12" twist. Since he asked; "what do we suppose about those loads in the .308 with a 12 twist?", I answered as if he was talking about his rifle having a 12" twist. That being the case and the fact that Sundog gave little information about his barrel I hesitate to guess at the velocity. My answered was predicated on the fact that the 28 gr load was accurate and a 2 gr increase to 38 gr load was not accurate. That usually is indicative of the bullets RPM exceeding its threshold. Excuse me but I do not buy off on the "harmonics" gambit. A good heavy barrel that is accurate will continue to be accurate. If there is inaccuracy then there is another reason and it is not harmonics.

"How will your test prove 100 percent that rpm is the accuracy killer? "

Read how the test is conducted. Read the results of the first test as reported in Chapter 2. Perhaps you will then understand that I did not "select" RPM. The test results are demonstrating very clearly that it is indeed RPM.

Larry Gibson

[Tiger]

None the less Larry, the question I asked still stands. Will the accuracy of the four different burn rate powders be on the same level if all have the same velocity? I don't think so, in fact I know they will not. It's not rpm Larry.

Ralf

[Tiger]

None the less Larry, the question I asked still stands. Will the accuracy of the four different burn rate powders be on the same level if all have the same velocity? I don't think so, in fact I know they will not. It's not rpm Larry.

Let me restate that, it's not rpm outside the barrel.

Ralf

[Tiger]

Sorry about that double post as I was trying to edit the one.

Runfiverun I'm not saying that rpm has nothing what so ever to do with the accuracy, I'm saying the damage, if any is occurring, is happening in the barrel. Then of course rpm will amplify that damage outside the barrel. The different versions of 4895 are so close to one another I don't think there would be a difference either, but I did say four powders with different burn rates meaning entirely different burn rates, which you did answer too.

So why do you think with the four different burn rate powders the accuracy would be different? Will you tell me because of the different pressure applied to the bullets?

Ralf

[sundog]

12 twist hvy bbl Rem 700 VS. I have some WQ WW/RS 314299 that I'll repeat the test with as soon as the wind dies down a bit around here.

[Larry Gibson]

Ralf

Excuse but what does your question have to do with a test of 3 different twist barrels? Absolutely nothing. Yes they are probably different with 4 different burning ratesd to the same velocity. What the heck is your point. My test was the same load to the same pressure to the same velocity. I tested the difference that RPM makes. The test demonstrates it is RPM. Please come back with a more pertinant question or quit wasting my time with rediculous comparisons that are not valid.

Read the test Ralf, I am seriously thinking you have not done that.

Larry Gibson

[runfiverun]

i don't think it is so much the different pressures
but when where and for how long.
like bass [i believe] said about 3000 posts ago pressure at the muzzle has an effect
also.
10000 psi at a bad crown is way worse then 4000.
a hard slam into a short throat, is probably not as bad IMO as it will be re-worked some in the bbl [ possibly for the better] any way.

bad is still bad, and rpm's is the killer.
i dont think it is the end-all but it sure don't help.

[Tiger]

Ralf

Excuse but what does your question have to do with a test of 3 different twist barrels? Absolutely nothing. Yes they are probably different with 4 different burning ratesd to the same velocity. What the heck is your point. My test was the same load to the same pressure to the same velocity. I tested the difference that RPM makes. The test demonstrates it is RPM. Please come back with a more pertinant question or quit wasting my time with rediculous comparisons that are not valid.

Read the test Ralf, I am seriously thinking you have not done that.

Larry Gibson

First your test only proved there was a difference in accuracy in your particular rifles and only for the powder/powders you selected, along with the loads. That's hardly conclusive and representative of all the different rifles and loads and bullets out there. How can you be sure the barrel harmonics were exactly the same with all the test rifles especially when the twists are different. They say the harmonice or vibrations of a barrel upon firing are like a sinew wave on an oscilloscope. The accuracy depends and what position that muzzle is in when it releases the bullet. You have no test to determine that. Perhaps you could affix such a tuning device to your muzzles and then shoot for the best accuracy with each twist.

What was my point on the different powder burns rates? To point out and to get you think that there are more then one , two, three, or more influences on the bullet that cause it to do what it does do.

Waste time? From watching the forum it's obvious to impress many members with elaborate tests. Many have gotten accuracy at higher rpm then you ...45 2.1, Bass...and others who probably don't care to mention it, but you can not accept that.

Runfiverun

All those things you mentions in your last post are still connected to pressure one way or another.

Ralf

[onceabull]

A "newbie"with nary a post except on the latest "RPM" thread ??? a water carrier for ?????..... Onceabull.....

[runfiverun]

tiger

larry is testing rpm's
he knows how to make a rifle shoot
what he has/is doing is making everything as comparable as he can

same brass boolits powder and bbls as close as anybody can reasonably get them.
i personally think that what he has shown so far has proved this out.

as far as the velocity / pressure question it would mostly show up as
vertical dispersion mostly anyway.

[leftiye]

Sorry about that double post as I was trying to edit the one.

Runfiverun I'm not saying that rpm has nothing what so ever to do with the accuracy, I'm saying the damage, if any is occurring, is happening in the barrel. Then of course rpm will amplify that damage outside the barrel. The different versions of 4895 are so close to one another I don't think there would be a difference either, but I did say four powders with different burn rates meaning entirely different burn rates, which you did answer too.

So why do you think with the four different burn rate powders the accuracy would be different? Will you tell me because of the different pressure applied to the bullets?

Ralf

Ralf, we all have said that (probly several times) before about the RPMs probly having an effect both inside the barrel, and later. I think it is interesting that there is Nothing that we can do about RPM besides buying a barrel with a slower twist, or slowing the velocity - if rpms were THE culprit - with a given alloy boolit. On the other hand, there are myriads of things concerning alloy, lube, powder burn rate, gradual versus sharp leade and other reloading factors that will make higher velocity boolits shoot more accurately. Ironically, when we buy that slower twist barrel it itself may not shoot cast well, and our money may be wasted.

Larry, Concerning 28 grain load being accurate, and 30 grain load not grouping well- "That is usually indicative of the bullet's rpm ecxeedingits threshold" (OR SOMETHING) not necessarily, your opinion.

[runfiverun]

if larry's tests prove out here
it would sure simplify load start.

think about it , boolit hardness ,pressure, twist rate, velocity.
it would sure make picking a starting load close to where you want to be
a lot easier.

if you remember to write down a few simple formulas
[ which i will have to find again]
to figure your leads compressability, your loads reduced pressure.
your twist's rpm's.
pick three or so powders that all fit the bill and start them all
in the same place, put them over a chrono. and tweak the best one.

[leftiye]

run5run, I disagree. The only thing that larry's "principle" does is to help us further understand inaccuracy. ALL of the things that one does about inaccuracy remain the same. We're still faced with the situation that accuracy at slower fps is easier to attain, and that if you want to go faster, you have to do better (do your homework). The better you iron out the variables that reduce deformation, the better you'll do at high velocities. (RPMS only act upon the defects anyway - Ironically, if you were to have perfect boolits, and perfect loads, accuracy more than likely wouldn't be perfect anyway). Most of this at present constitutes a basic formula or framework guiding us on how to proceed. After that you must analyze your results and adjust your loads, and rifle, etc..

Another side trip - if you just want to shoot paper, speed is somewhat not an issue. If you want to shoot game, and want boolit expansion, very high velocities aren't needed or wanted as soft lead is needed (relatively), and you will either make a surface wound with insufficient penetration, or mutilate your dinner. Pure lead boolits at 2000 fps. make excellent varmint boolits, but you won't hit anything without a paper patch (or similar) and maybe not then, and you won't want to eat it afterwards.

[Tiger]

A "newbie"with nary a post except on the latest "RPM" thread ??? a water carrier for ?????..... Onceabull.....

Newbies be forewarned the Onceabull Department of Knowledge must certify your knowledge before you can post freely or acquire 10,000 posts.

I don't see you contributing anything to this thread. Probably because you can't.


Ralf

[runfiverun]

leftiye
do my homework?
pay attention to the test please, what larry is doing is homework.
i don't think i ever heard him say that all tests are being cut off at 1800 fps
i believe he said he will test to see at what velocity/rpm that each twist rate will lose
accuracy. [ i believe he also said he will try slower powders to try and get it back,
as well as other sn/sb nixes]

which is fine with me as i usually shoot most of my g/c rifle boolits in the 2000-2400
fps area anyway.
depending on how they regulate with my sights @100 + yds
if you are thinking
that either i or others [larry] believe that you can just pour up whatever
lead you find , into what mold ya got, and shoot it to x amount of rpm's
because that is in the magic rpm range.
you are totally missing the whole point here, what larry is doing is defining what
causes the "sweet spot" in load development.

this is what i am taking from these tests.

[leftiye]

Boy, did you lost me! The homework referred to was what we have to do in getting a load right or improving it (nothing to do with you personally). Sorry if I wasn't more clear, no offense meant to you anywhere in my post. But Larry don't need no help in defending hisself. Don't see 1800 fps anywhere in my post.

[Tiger]

runfiverun

That sweet spot post you just done sounds a lot like a barrel harmonics situation.

I have been doing some searching back through the old post and it's a lot of work. I believe it was Buckshot that has done lots of shooting with the Swede. It appears that the Swede is difficult for many to achieve good accuracy with especially at the higher velocities. If I read correctly Buckshot set a limit of about 1900 fps and still maintain decent accuracy. That gives the bullet an rpm of 182400 which is outside of Larry's rpm range. We know that the 6.5 bullet has been a problem caliber to shoot accurately at higher velocities, but yet judging from Buckshot's pictures of his targets he has done well at 1900 fps and 182400 rpm with a long small diameter 6.5 bullet. That's not to say that all his targets were fired at that same 1900 fps. I also read that he was experimenting with some other bullets for higher velocities yet, but ran out of them before he could verify a conclusive test. It looked like what he had achieved more then likely did up the velocity level. That means even more rpm for that 6.5 bullet. Today I was also looking at the Lyman cast book. I was in the 6.5 caliber section and the 6.5 Mannlicher data stuck out. They had quite a few loads in the higher velocity bracket say 2200 fps. The rifle they used had a 7.5 twist so that gives us 211200 rpm. A load for the 25-06 gave a velocity of 2677 fps (at 44,700 psi too). It had a 10 twist which gives us 192744 rpm. There are more examples. All out of Larry's rpm range. What is my point? Lyman, which tested all these loadings, would not publish loads that were unacceptable as we know this would come back on them. Unacceptable would mean no usable accuracy or either barrel leading up badly.

So is it okay that I disagree with Larry? Some say no. Who can explain the above result by Lyman?

Ralf

[runfiverun]

buckshot isn't the onlyone 45 2.1 , manley j.t. and others have
worked with the 6.5 swede with good results, lots of others have had many,many
problems with it if you can find it probably on page 2 or so
there is a thread on the 6.5 that started all this testing.

i am forming an opinion that the smaller calibers fare better with cast as higher
rpm's. just don't have any tests to pull memory from
i do have a 7mm mold coming so i can try it against a 30 cal

same boolit design from same pot of 4/6 mix g/c and going to try twist etc...

and i know that larry doesn't need any help!!!!
no offense taken
i enjoy hearing all this stuff from everybody it is all different opinions and some valid facts
you know, the well then how come this, and the how come that.
it is all the fun we have and the reason for this web site.

hell ifit works for one guy it ought to work for everybody?
the more we find out from the more sources may point to what we should be doing
or what may be wrong if what we tried doesn't work.

as far as the lyman manual thing i don't know i do know that they will show higher velocities

at times and then disclaim their data saying that excessive leading occured at xxx velocity
with cast data they give you boolit weight and velocity data.
they have no way of knowing what lead you are going to use and if you have any problems
you will be told that you didnt follow their recipe exactly.

[Larry Gibson]

Ralf

Lyman doesn't test it's loads for accuracy by shooting groups. The "accuracy" loads are judged so based on internal ballistics, i.e. constistancy of pressure and velocity. Because loads are listed does not mean they are accurate.

Perhaps besides actually reading the test I've done so far you should read the Lyman Manual too.

Larry Gibson

[leftiye]

My experience too. - Many of lyman's loads are way hotter than will shoot well. Pressures may be consistent, but you might (some remote possibility LOL) , just MIGHT get a little (?) leading.

[carpetman]

Larry Gibson "consistancy" of pressure. No longer impressed it's consistent so therefore consistency.

[Tiger]

runfiverun

It's harder to shoot the larger calibers at higher velocity because if you do they usually have a lot of recoil to them. That of course depends on the caliber but say 35 caliber and up the bullets are much heavier most the time so they start to hurt the shoulder. Too they normally don't have a fast twist if one is wanting to see if the rpm is what destroys accuracy.

Larry

Are you a politician by chance? Did you see anywhere that I posted that Lyman tested by shooting groups? No matter by which means they gather their data they still are not going to publish real bad data.

I remember Bass speaking about the pressure on the base of the bullet as it leaves the muzzle. We know the gases are trying to escape too. I am sure some of you have examined recovered bullets. Me too. I noticed on the low pressure ones the gas checks did not look too bad. Another story on the higher pressure bullets. The gas check, if they were still on the bullet, look like they go through holy hell. You may have noticed that it seems the gas pressure gathers, collects, or peaks in the center of the base and pushes in there making the gas check look like a cup. I think I saw a post by Felix saying he agrees with that. So what I am getting after is the more I think of this cupped or somehow damaged gas check the more I think what Bass said. Larry you know well that factory jacketed bullet bases rarely ever have this condition. So many Bass is right about the pressure on the base of the near the muzzle and as it leaves the muzzle huh? I would agree that an undamaged base whether it is a jacketed bullet one or a gas checked one is not going to be as accuarate as an undamaged one.

All of you see that there are way too many variables involved in cast bullet shooting to make a conclusive decision about what causes accuracy to go bad.

Ralf

[runfiverun]

so we aren't going to try and test what variables we can, to try and see which
ones work. better.?
the only ones trying to better castboolit shootin are cast boolit shooters.
when i bought my last rifle there were no instrucions as to what bullets to shoot in it
cast or otherwise, it didn't even say what twist rate the bbl had.

but my next one will probably be built out of parts that i pick and choose and then have assembled how i specify.

[Larry Gibson]

Larry Gibson "consistancy" of pressure. No longer impressed it's consistent so therefore consistency.

I'm tellin' ya, this computer doesn't know that!

Larry Gibson

[oso]

There must be an advantage to rifling or we'd all be shooting muskets with 0 rifling. We might all agree, or without too much argument, that 32 tuns/inch is probably too much twist. Greenhill came up with a formula to find "optimal" twist rate for bullet weight, diameter, specific gravity, bearing length and velocity (one factor is 150 for slower bullet velocity and 180 for faster velocities.) As I see it Larry is experimenting to see if bullet velocity could be fine tuned as a factor to consider for .30 cal cast bullet accuracy for the average caster with the twists he has available. He's doing some great thinking and testing. He's not writing a new gospel and no one has to use the information presented. The real problem here is that some think he is not getting enough non-constructive criticism. Thanks Larry for the information, and I appreciate your patience.

[Tiger]

Stabilization Mythology
Sit down in a comfy chair, and grab a beverage of choice before you start this one folks, because it's going to be long, and somewhat obscure.

Tonight, I'm back once again to address a common firearms myth; this one actually a bit more technical than most. We're going to talk about bullet stabilization, specifically that of 5.56 nato and .223 bullets.

This is a common subject of misinformation, because most folks don't understand what bullet stabilization is, or how rifling really works for that matter.

Worse, 5.56 is the default chambering of the AR platform rifle, which is the default rifle choice for tactical Tommies everywhere; and as we all know mall ninjas love nothing more than incorrect information.

Actually, to be fair, even otherwise knowledgeable gunnies don't generally understand the variables involved in stabilization, because they don't have a background in the physics or aerodynamics of external ballistics; and because they hear a lot of bull, that sounds kinda OK, and since they don't know any better, take it as truth.

Before we even begin, let me refer you to the best source on ammunition for the AR platform, and 5.56 nato in general; the ammo oracle. There really is no better collection of information on 5.56 ammunition anywhere.

Also, these same principles apply to all elongated bullets (i.e. anything that isn't a ball), no matter what the caliber is; I'm just using the 5.56 as an example, because it is the most common rifle available with many different twist rates, and also the chambering for which the most misinformation is circulating.

Ok, down to business

First, what is stabilization and how does it work?

Modern rifling has a twist, to impart spin to the bullets leaving the barrel. This spin helps to make bullets in flight more stable in two ways:

First, the spin causes gyroscopic stabilization; which is just like how it sounds. A spinning mass resists being disturbed off the axis perpendicular to the direction of rotation due to gyroscopic inertia; which is rigidity in space induced by radially symmetric (which means the forces are the same along all radii - i.e. identical all the way around in all directions) centrifugal forces.

This is the primary component of spin stabilization for pointed bullets (ball bullets are primarily stabilized aerodynamically, because they tumble as well as spin), and it's force component significantly outweighs most of the aerodynamic components of ballistic stability which I will describe in the next section.

In simple English, bullets spin like a top, and they don't "fall over"; just like a top doesn't.

Now, the second element of stabilization caused by rotation, is aerodynamic. Objects rotating in a fluid (and that's what air is), generate radially symmetric lift (again, this means the lift is the same in all directions).

Anyway, this means the bullet is neither pulled down, nor pulled up by these forces (technically this is incorrect in some very small and specific ways, but for purposes of this illustration it is a valid assumption); or rather it is pulled down and pulled up, as well as pulled to all sides and in all radial directions, equally. When something is being pulled in all radial directions equally, just as with a gyroscope, it resists deflection in the axis perpendicular to the pulling forces.

There are two other components of aerodynamic stabilization, and those are form lift (which is the lift created by the shape of the object itself as it passes through the air) and the angles of attack and incidence; but neither are useful in this discussion at the moment.

The first common myth about stabilization, is that the heavier a bullet is, the faster it must spin to be stabilized. In fact this isn't really true, heavier objects gyroscopically stablize at lower rotational velocities than lighter objects (the flywheel effect); and though the aerodynamic stabilization componenst required for heavier objects are greater in magnitude than for lighter objects, the differences in weight and relative difference between force components, between different examples of the same diameter bullet loaded for the same cartridge, are generally small enough that the aerodynamic component of the stabilizing forces required do not change significantly.

The issue with bullet stabilization is actually length not weight; but because the diameter of the bullet is fixed (we are after all talking about different bullets in the same caliber), there are really only three things which generally change the weight:

1. Profile: if the bullet is less tapered, then it will be heavier for a given length, but generally less ballistically efficient (though not always).

2. Construction: If the bullet is solid copper it will weigh less for a given length than a jacketed lead (the 37gr copper solid varmint bullets for example, are the same length as 45gr jacketed lead bullets). If the bullet is a tracer, or steel penetrator type armor piercing it will also weigh less than a solid lead jacketed bullet for a given length. Also if a bullet is hollow (or partially hollow such as some MilSurp .303 or 7.62r loads), it will obviously weigh less for a given length.

3. Length: The longer the bullet, presuming construction and profile remain the same, the heavier it will be

Generally, this means that a change in length is the same as a change in weight; and since bullet length isn't commonly discussed or published; and because weight is a more important component in interior ballistics, we mostly refer to different bullets and loadings by their weight.

The reason why length is important, is because of the center of gravity, and center of pressure of the bullet; and their relationship.

Center of gravity is a commonly known (if not necessarily commonly understood) concept; which simplified, is the balance point of the bullet. If you very carefully put the bullet on a razors edge at the exact center of gravity, it would in theory balance and just sit there, stable.

The center of pressure is a similar concept; in that it is the point where the aerodynamic forces acting on the bullet are balanced along the longitudinal axis of the bullet (the length).

If your center of gravity, and center of pressure are identical, then your bullet will exhibit exactly neutral stability. This means that the bullet will neither resist deflection, nor will it correct or accelerate any deflection that occurs. Again, if you balance the bullet on the razors edge, it should in theory stay in the same spot until it's disturbed by outside forces.

Of course the center of pressure on a bullet is rarely exactly at the center of gravity. Not only that, but as a bullet accelerates, decelerates, and changes it's angles of attack and incidence (the angle between the longitudinal axis, and the direction of travel; and the relative angle between that axis, and a plane perpendicular to gravity), the center of pressure will change; sometimes radically. Changes in pressure and balance, cause instability.

Now, there is a component of the forces on a bullet called the moment of inertia. The further the action of a force is away from the center of gravity of an object, the greater its moment of inertia. A given force will have a greater effect on an object, at a greater moment of inertia.

In simplified terms, the further away from the CG the force is, the more leverage it has. The more leverage a given force has, the more change it will induce.

How does this apply to bullets in flight?

Well, the longer the bullet is, the greater the moment of the forces, therefore the larger the effect of aerodynamic forces on the bullet are; and more specifically the more they change as the rotational and linear velocity of the bullet change. Additionally, longer bullets have more chances for imperfections, and imperfections also cause changes in the effect of aerodynamic forces.

The very definition of stability is resistance to change; and the more change there is, the less stability there is.

OK, so that what stabilization is, and how it works, but why is it important?

Simply put, stable bullets are predictable.

If a bullet is stable in its flight, it is more likely to hit the same spot as the last bullet.

That is precision.

If a bullet is stable in flight, it is more likely to hit what they are aimed at.

That is accuracy.

Precision produces grouping; accuracy produces scoring (or stopping); both of which are kind of important in the application of firearms for both competitive and practical purposes.

Encapsulated: stable bullets are both more accurate and more precise. Longer bullets require more stabilizing forces to maintain stability. Faster twist means greater gyroscopic effect, and greater stabilizing aerodynamic forces.

Now, the second major myth is "Overstabilization".

Some folks believe that you can "overstabilize" a bullet, and therefore reduce accuracy. For all practical purposes, there is no such thing as overstabilization, so generally faster twist doesn’t hurt accuracy with lighter bullets...

Except in reality it does, for three reasons: unbalanced aerodynamic effects, out of balance bullets, and structural failure due to overspin.

The problem with very light bullets, its that they are more lightly constructed. This makes getting them perfect and consistent and perfectly balanced more difficult. Additionally, any imperfections there are, will have a greater effect because they do not have the mass (and thus the inertia) to resist destabilization.

The faster bullets spin, the more aerodynamic lift is generated. Though the lift is radially symmetrical, thus it balances itself out as explained above; the totality of force is still greater, and therefore there is greater potential energy in case of upset. Very slight imperfections in the bullet cause aerodynamic disturbances which upset and partially offset the stabilizing effects of faster spin.

Those same imperfections, along with slight variations in the distribution of mass throughout the bullet, also cause out of balance “wobble” or precessional destabilization (as opposed to precessional drift, which is motion in the axis and direction of rotation due to gyroscopic forces).

All of these factors upset the bullets to varying degrees, causing instability, and reducing accuracy and precision.

This is true of heavier bullets as well; but their greater inertia makes the forces required to cause upset far greater; as well as increasing the tendency to damp out upsets and return to stable orientation.

Finally, because lighter bullets are more lightly constructed, they are also not as strong; and the faster rotation of higher twist rates causes the internal stresses on the bullet to be higher (torque, centripetal and centrifugal force, shear forces between the layers of construction etc...); which may cause the bullets to disintegrate either in the air from imperfections in the bullet, or on impact; without penetrating the target.

This is common with the lightest varmint bullets driven at very high velocities, and is sometimes called "poofing", or "going poof", because when the bullet disintegrates there is sometimes a visible puff of lead and copper residue in the air. This tendency is unsurprising when you consider that a bullet traveling at 4000 feet per second, may be rotating as fast as 400,000 RPM.

Earlier I said that for all practical purposes, overstabilization doesn't exist in the real world of shooting. This isn't to say that too much gyroscopic stabilization can't occur, but that it's effects are generally so minimal as to be insignificant.

Now, some folks will tell you that you can stabilize a bullet so much, that the bullet wont follow a proper ballistic arc; the gyroscopic effect causing the bullets nose to always point upward at the original angle the bullet was fired at, and cause the bullet to keyhole the target.

To a slight degree this can be true; but only at extremely long or extremely short ranges does this become an issue.

Even some otherwise informed and reputable sources (including the ammo oracle) will tell you this is a problem but this is simply not true of almost all bullets, fired at almost all angles. You would need to have a very short, very heavy bullet, fired at an extreme angle, with a very high twist rate, and with a shape that puts the center of pressure in an odd relationship to the center of gravity, for this to significantly reduce observed accuracy at anything but the absolute shortest, or longest ranges possible.

A bullet in flight will naturally tend to stabilize in a ballistic arc, with the base of the bullet behind the nose, because as the angle of attack changes, the center of pressure will move slightly behind the center of gravity. The base of the bullet acts like the trim tab of an airplanes tail; it tends to react against deflection, and oscilate in a cycle of reducing magnitude until the various forces on the bullet balance out, and stable state is regained.

In general when looking at bullet flight, gravitational forces, thrust forces, gyroscopic forces, and aerodynamic forces will naturally find a balance of ever decreasing magnitude, to produce a smoothe arc. Gravity itself will tend to pull the nose of the bullet down, while deflection lift (equivalent flat plate effect, also called weathervaning) will tend to keep the base of the bullet up. This aerodynamic tendency should overcome any tendency to maintain the initial angle of incidence because of high gyroscopic forces. In a vacuum, that same smoothe arc exists, but the orientation of the bullet will not be stabilized aerodynamically; and the bullet will tend to remain oriented in the intial direction of firing.

The only cases in which this would not be true, is if the range were so short that the bullet had not had time to straighten out from an initial disturbance, or if the range were so long and velocity so low that combined with a very high angle of incidence, a very high angle of attack, and a very high twist rate, the aerodynamic forces on the bullet had reduced to the point where the bullets rigidity in space was stronger than the weathervane effect.

There is one particular component of force that can slightly reduce accuracy due to overstabilization; and that is through precessional drift as described above.

Precessional drift is when a rotating object tends to translate horizontally in the direction of rotation, due to gyrosopic momentum overcoming static inertia (the centrigual force of the flywheel effect pulls the flywheel sideways). If a very light bullet is spun significantly faster than required for stability, at long ranges this precessional drift can slightly reduce accuracy. The heavier, and the longer, a bullet is; the more it will resist this tendency.


Please forgive me if this post was too long, I apologize. I was afraid that most would not read it if it was a link.

Ralf

[Larry Gibson]

oso

Your comments and objectiveness are appreciated.

Larry Gibson

[Larry Gibson]

Ralf

I am amazed at the very sudden mastery of the English language and technical aspect of bullet stabilization your last post demonstrates. Could you kindly give us the source of your last post? Considering the one or two mispelling you may have typed it. However plaguerism or simple cut and paste without quotation marks at least, is somewhat frowned upon. BTW you with that discertation you fail to provide a "bottom line" or what your point is. Matching up that last post with numerous of your previous posts demonstrates considerable change of thought if you agree with the author of that last post. I find it quite interesting because it states numerous of the principles that govern exactly why RPM causes inaccuracy of an unbalanced bullet.

Larry Gibson

[Tiger]

Larry,

I pointed out very plainly at the end of that post that it was from a link and why I posted what the link said.

I see how you operated, thank those that agree with you and give negative remarks to those who don't. You even accused me of plaguerism and I have called you by no names.

About the post perhaps you didn't read it so closely as it said rpm didn't have that much influence. Go reread it.

You look for the fellow that wrote it, Chris Byrne, for your punishment of the accusations you have made. Wow, to be on the disagreeing side of you is to be your enemy Larry, hey?

Ralf

[runfiverun]

ralf
excellent post, can't believe you didn't mention the greenhill formula
which says that my boolit should be shot in a 14 twist in 308 and in a 12 twist in 7mm
same length smaller diameter.
whats up with that?

[carpetman]

Larry Gibson--What is a pell? You mentioned one or two mispells. I thought pell was a city in Greece.

[runfiverun]

i met a miss-pell once when i was in guam :bigsmyle2:

[Larry Gibson]

Ralf

Link or not it's just common courtesy to give credit where credit is due.

“as it said rpm didn't have that much influence”

Exactly where does it say that? I presume that was your bottom line?

Thank you for identifying the author.

Larry Gibson

[Larry Gibson]

Larry Gibson--What is a pell? You mentioned one or two mispells. I thought pell was a city in Greece.

Dog gone...did it again, LOLs.

Larry Gibson

[Larry Gibson]

Oh, Ralf, one other thing; "enemy"....not hardly.

Larry Gibson

[felix]

run5run, what are you talking about in relation to your two guns? Are you questioning the parameters for the various twist formulas out there? ... felix

[Slowpoke]

Larry Gibson--What is a pell? You mentioned one or two mispells. I thought pell was a city in Greece.

You should talk

"Getting 120 bullets to the pound your put doesnt go down very fast" :)

good luck

[carpetman]

Slowpoke---Im missing something on that one????

[tube_ee]

Sorry, I've been out of here for a few days, so I wasn't able to respond to your responses right away... work sucks, but being broke sucks more.

Within the limits of your experiments, I think we agree. Assuming a constant number of defects and distribution of those defects within the bullet, the faster the bullet is turning, the greater the effect of those defects will be. Basic physics at work. And your results show this.

It is the idea of a "threshold" that I take issue with. A threshold implies something unique to that parameter, that cannot be overcome.

As a newbie to cast rifle bullets, although not to shooting and reloading, I'm more interested in what I can do to maximize the performance of the bullets I cast in the guns that I shoot. Velocity is an important component of bullet performance in the field. Considering two identical bullets, the faster one will generally kill game better, assuming that it is not moving so fast as to come apart too quickly.

So if you're correct, and most cast 30 caliber bullets don't shoot well above ~2000 fps, what can we do to change that? No one would doubt that pushing that up to 2500 fps would yield more penetration, more reliable expansion, and a more easily usable trajectory in the field.

Thank you for your work in this area, I'm learning a lot.

--Shannon

[runfiverun]

felix
yep why with two bullets the same length but only 15-20 grains in weight
difference. and a diameter difference of .016 that a formula based on boolit length
would show a 14 for one and 12 for the other.

[Larry Gibson]

Tube ee

Conceptually we’re talking the difference between a threshold and a limit.

“A threshold implies something unique to that parameter, that cannot be overcome”

It is a “limit” that we can say “can not be overcome”. A “threshold”, on the other hand, can be “stepped through” so to speak. That stepping through may be difficult but we should be able to do it. This issue usually arises around the issue of regular cast bullets in rifles when someone tries pushing them above the 1800-1900 fps range. Most often the rifles have a 9-10” twist. Accuracy is good up through that velocity range but when pushed higher accuracy falls off.

The question I’m looking at is to define if there is a RPM threshold. I am doing this by isolating certain aspects that affect the accuracy of the bullet. I am accurately measuring the internal ballistics, the external ballistics and the terminal ballistics in this quest. Then I shall continue to narrow down things we can do to the rifles, bullets and loads by isolating them and measuring their effects on the bullets accuracy. I shall focus on those things that really make a difference in maintaining cast bullet accuracy at higher velocity and RPM.

Some here don’t grasp the concept of this test and what its real objectives are. Appears they want to go off on tangents not really related to this experiment or how one properly conducts a test that give results we can measure. It is the result of a comparative analysis that we must seriously consider. We all use analogies but I am trying to get away from them by conducting tests that actually tell us what is happening to a cast bullet and how it is affected in flight.

I also am “more interested in what I can do to maximize the performance of the bullets I cast in the guns that I shoot.” I am especially interested in facts not guesses of analogies. Thank you for your interest and I’m looking forward to more of this type of input.

Larry Gibson

[felix]

R5R, unit weight is a constant across all the boolits to be compared, and therefore typically hidden in the lesser formulas used for twist calculations. However, the radius of the projectile is a quadratic in the majority of twist formulas, and therefore causes a drastic change when compared to a weight change. ... felix

[sundog]

Y'all ever wonder why so many single shot shooters run relatively low velcities? Other than shooting plain base boolits, there is a consensus that a boolit that is just barely stablized is most accurate. They tend to use slower twist, also. These same guys also tend to shoot heavy for caliber boolits. Seems like there may be two things going on here: rpm amplifies deficiencies; and weight dampens deficiencies. Something to think about.

In the meantime, I've got my boolits and brass ready to repeat my test I posted about. .308 with 314299 and 28 and 30 gr 4895. This time however, the boolits are WQ instead of AC with a very significant difference in hardness. I have no tester other than a thumnail, but the WQ are noticeably harder. I'll probably load tonight, and maybe get to the range this weekend. If not this weekend it will Saturday the 26th after high power.

[Tiger]

Larry,

You sound like that famous cowboy actor John Wayne with that "not hardly". I can hear him now.

Sundog,

You sound more and more like Larry now, don't fall into that easy trap. Did you read what I posted what Chris Bynre wrote?

Here's a short revisit: Encapsulated: stable bullets are both more accurate and more precise. Longer bullets require more stabilizing forces to maintain stability. Faster twist means greater gyroscopic effect, and greater stabilizing aerodynamic forces.

He actually says that the greater the gyroscopic effect the greater the resiistance is to disturb the bullet.

I didn't post the myths Chris wrote about boatailed bullets or maybe your statement on them would have been omitted.

More then likely many reasons why single shot shooters do what they do, but hardly likely it's a high rpm reason.

Ralf

[felix]

Ralf, you would be correct only if and when the projectile remains consistent to form, AND the ambient remains consistent throughout the trajectory. How many times have you driven a car with 4 tires perfectly in balance perceptively throughout 30-120 mph, except for being lousy at 65-70 mph? Which tire is it? Maybe more than one? What about the road? Yes, Larry is on the right path. He is trying to define where that dead zone is. It's hard to do sometimes, but always try and keep in mind that math is used to explain nature rather than vice versa. ... felix

[Tiger]

Felix

A tire is not a good example to compare to a bullet. For one thing you know that a tire is not round at high speeds. It is amazing that a tire balances as good as it does considering how out of round it is at high speed. Could this be because of the gyroscopic effect making things work?

Sundog mentioneed boattail bullets so I copied the post on them by Chris Byrnes. Larry pay attention as I tell you again I copy this. By the way if there were spelling errors in that very first copy of Chris's work they are his not mine. Not to say that I do not make spelling errors as it is obvious that I do.

Here it is:

Boattail bullet stability, and the bearing surface myth.

Some folks believe that boattail bullets are more stable, and will stabilize at lower twist rates; for varying reasons, but often because they believe that the length of surface contacting the bore makes a difference in stability.

Unfortunately, this is entirely incorrect. Sometimes boattail bullets are more stable, especially at extreme ranges; and they are certainly more aerodynamic in general; but not all boat tail bullets are more stable in all loadings or situations, and if they are more stable, it has nothing to do with the length of the bearing surface of the bullet.

The reason why boattail bullets sometimes stabilize better, isn’t because of surface contact with the bore. Why would twist rate or stabilization have anything to do with surface contact with the bore?

The primary reason boattails can sometimes be more stable, is because the boattail base is less susceptible to aerodynamic upset; and is also less likely to be nicked by a rough crown or bore imperfection. Additionally, what imperfections there are have less effect on the bullet because they are at a smaller radius (and thus exhibit lower gyroscopic forces), and have less aerodynamic pressure applied to them

Often however, very light boat tail bullets are MORE susceptible to upset, because under some circumstances they do not exhibit as much positive stability (the tendency to damp out oscillations from a disturbance) as flat based bullets, as they have less incident flat plate area behind the center of pressure.

Hollow base bullets are even more interesting, in the effects that they have on turbulent flow, and base upset; as well as their deformation characteristics out of the bore which can cause a shuttlecock effect; but that's neither here nor there.

Some folks believe the bearing surface length is important, without regard to bullet design, but this too is incorrect.

You’ll note that the reason why twist rate increases stability, is because faster rotation means more aerodynamic forces (radially symmetric lift) as well as more gyroscopic forces. This has nothing to do with bearing area. Let me say this again: The bearing area and rotational velocity of the bullet in flight, are not interrelated.

You could have nothing more than a bearing band 1/8” long, and the bullet would leave the barrel spinning at the same rate, and with the same rotational energy (though a slightly higher linear velocity presuming gas seal integrity was maintained) as if the bullet were a perfect cylinder (presuming the rotational forces weren't so great that they distorted the bearing band of course).

In fact bearing bands are used by many large diameter (.50cal and above) rifled projectiles; as well as many projectiles used in 18th and 19th century in muzzle loaders; because the use of bearing bands reduces friction and fouling. Also some cast lead revolver bullets use a bearing band design for the same reasons.

Heck, boat tail bullets are even longer per given weight than flat base bullets are, so they would have an even faster required spin rate if it weren't for the factors I spoke of above. If you can shoot heavier boat tail bullets through a slower twist barrel accurately, it is for the reasons I mentioned above... welllll and one more thing

Now, I said up near the beginning of this piece, that form lift, or rather to be more specific aerodynamic characteristics based on shape, could be important; but it wasn't relevant to the discussion here specifically with regard to twist rate, length, weight, and stabilization.

That's not strictly true; because different shapes of bullet, even with identical weight and length, will have different aerodynamic characteristics based on their shape. It's just that for the most part, those aerodynamic differences are quite small between different spitzer bullet designs, different roundnose bullet designs, different flat base bullet designs, and different boat tail bullet designs.

Most often, bullets compared with each other will all be of a single design type i.e. they will all be pointed nose or all be round nose etc... There can be significant aerodynamic differences between round and pointed nose bullets, and flat base vs. boattailed bullets.

Some shapes exhibit greater tendencies toward positive stability. Some shapes have greater stability at lower velocities, and less stability at higher velocities or vice verse. Some shapes deal with things like shock waves, turbulence, or flow separation better than others.

This relates to boattail bullets specifically, because overall, the boattail spitzer (meaning pointed at the front with a gentle ogive, and tapered at the back with a flat base behind the taper) is the optimal form for maintaining both stability and aerodynamic efficiency in the velocity ranges we are dealing with for rifle bullets. Sharply pointed bullets with a tapered base generally deal with shockwaves and moving centers of pressure better than other bullet designs; resisting shockwave upset and turbulent flow upset better.

So yes, often boattail bullets will be more stable; but that doesn't necessarily mean they will stabilize at a lower twist rate (though sometimes it does). It really depends on the relationship between the CG and the CP of the bullet, as described above, total aerodynamic forces, shockwave characteristics etc... and it's not something that can be easily predicted by a lay person, or by anyone without a supersonic wind tunnel and measuring equipment for that matter.

Simply, other than the general differences between pointed and flat or rounded nose; and flat or tapered base bullets; those comparisons are not useful for practical purposes.

Ralf

[felix]

Ralf, actually your writer buddy is making reference to a tire too, but unknowingly, especially in paragraph 6. ... felix

[leftiye]

OSO, No fine tuning going on. As larry has repeatedly said, he's not looking for the best accuracy, he's looking for the rpm that destroys accuracy. BTW that varies for boolit, alloy, gun, etc., how ya hold yer mouth (well, maybe not that last, but surely the others).

[Tiger]

Okay this is for Larry and the rest. This is not mine and here is the link:

http://www.bordeninstitute.army.mil/published_volumes/conventional_warfare/chapter4/Pages1-12.pdf

Here is the paragraph of interest: Rifling. The spiral grooves on the inside of a rifled barrel force a bullet to spin around its long axis as it travels the length of the barrel. The rate of spin that a rifle barrel imparts is determined by the weapon’s design, and for a typical rifle bullet is several hundred thousand revolutions per minute althought an im-pressive figure, the bullet’s angular velocity (that is, the velocity characteristic of a rotating object) is much less than its linear velocity; a value of about 250 fps is common.


Okay notice the rotation fps. It says a value of 250 fps is common. Yes it can change with different twist rate. This is some of what I have been trying to say that the rpm is not that great of a speed even though the formula for figuring it make you think so. Ask any of the top forensic ballistic doctors and scientist how much the spin of a bullet imparts to tissue damage and you will see that majority of them will say not much.

Also for you I have two videos of a bullet in flight in slow motion. Yes I know it's slowed down but even the linear speed in the film is much faster and obvious of the rotation speed of the bullet.

http://uk.youtube.com/watch?v=D4y-zgOn3vc&NR=1

http://uk.youtube.com/watch?v=ltF8iYNGovY&feature=related

Okay, let's hear the political denials and excuses please, hey.

Ralf

[sundog]

Yup, Ralf, I read all of it. Twice. Longer boolits have a better chance to have deficiencies and there is more than one force working them. The single shot boys seem to deal with all that pretty well most of the time. The also get fussy over powders, too. That has to do with ignition, pressure curve and the like. You can get a lot of different powders to give you the same MV but the curve will look different and not all of them will shoot good.

And, I'll take exception to your comment about falling into a trap. I've been shooting, casting and hand loading for a long time. I also know things that work and things that don't work. If something works for you and does not work for me, then it doesn't work for me. That's all there is to it. That does not mean closed minded.

Larry, press on.

[Tiger]

Sundog,

I get the idea from that writer that the heavier longer bullet has more gyroscopic energy to resist change. I believe the word stability has one meaning that is resist or resistant too??? I think he say somewhere there that the lighter bullets are more easy to disturb.

You remember some experiments done with picking a human off the ground with an airplane in a manner the plane does not have to land. They have a cable system, the man being connected, the plane with a hook. This is set up so most the shock of acceleration of the man can be minimized. Imagine if it wasn't and he was picked up and instantly into the same speed of the plane. That is how I look at the different pressure waves of fast burning to slow burning powders. You agree?

Ralf

[sundog]

Nope, Ralf, boolits are solids (with deficiencies) being pushed through a rigid (harmonics considered) tube to get going, and people being extracted (pulled -- jerked) are about 75%(??) water with joints that separate and bones that break. You need a better analogy. How about the human cannon ball at the circus? Accurate (hits the net), precise (hits the net every time), and best of all, survivable -- ya think maybe THAT guy has it figgered out?. Don't think for a second I have any preconceived notion how this is going to come out. I have suspicions, but then I've suspected lots of things in my life....

[runfiverun]

sundog, you may want to try some dacron with that load[ i use dryer lint]
it probably will help your s/d.
larry told me about this when i was having an e/s,s/d problem.
with starting about where you are, by the way my accuracy went away and came back and then got better when i took the load up, then back down a bit to regulate my 100 yd sights.
my hardness is just a bit over lyman #2. not wqed.

[Larry Gibson]

Ralf

To be compared to John Wayne is a great honor....not sure I deserve it but thank you anyway.

Larry Gibson

[Larry Gibson]

Ralf

I have read Chris Byrnes opinions before. He gives little or no reliable test results for his opinions. He is very astute at the use of English, especially technical jargon. However, his conclusions are unsubstantiated by test results. Many who have conducted tests have test results that differ substantially from his opinions. His speculation that bullets are affected by air pressure and fly basically like an arrow or with a shuttlecock effect have been disproved many times. Sometimes bullets do fly that way but many times they do not. Over stabilization is a problem with long range shooting. However for the issue at hand it is not relevant.

Larry Gibson