Excessive RPM -> Poor Accuracy?

[Maven]

All, mto7464 used 58gr. WC 860 in his K-31 and got miserable accuracy. Larry Gibson & Junior think the problem is excessive rotation, ~2,200fps by Junior's calculation. BA Bore disagrees.

Here's what I understand: (1) UNDER rotation results in an unstable CB trajectory and poor accuracy. (2) Lead (and wheel weights) is a cohesive metal, i.e., it doesn't fly apart when rotating rapidly...I think. Ergo, excessive RPM shouldn't pull the bullet apart in flight. (3) The K-31, with its 1:10.3 twist is a superbly accurate rifle with both jacketed and cast bullets, but there's a limit to how fast you can push CB's with it. 58grs. WC 860 strikes me as excessive and likely to produce bore leading with the attendant poor accuracy unless the CB's are very hard (heat-treated WW's, sized prior to heat-treatment).

Here's what I don't understand: (1) How can a concentric (via sizer and/or rifle bore) CB be "overstabilized" or over-rotated? (2) Other than a CB stripping or tripping the rifling, how does excessive RPM result in poor accuracy? I.e., are you suggesting that excessive RPM's magnify bullet imperfections to such a degree that they fly erratically?* (3) How do we know the poor accuracy is due to excessive RPM and not poor CB fit, poor CB design, excessive pressure for a given BHN, or any combination of and interaction between these? (4) Is there direct evidence of this or are we inferring this?

I'd appreciate hearing your thoughts on the matter as I'm just not getting it. Thanks in advance for your insights!


*I understand this, but the question is how erratic for a given amount of rotation?

[7br]

Maven,
If I remember right, it is called precession. Basically, go back to when you were a kid and spinning tops. When you first spin a top, it will wander around a central point. After a few seconds of slowing down, it will stablize and stay in one place. A few seconds later, it will slow down even more and go unstable. I supposed if you were on the border line of over stablization, you could get a tighter group at a farther distance than a shorter one.

[beagle]

Then too, all our cast bullets have voids in them and they're not just at the base. We discovered this when Petey was impact moly coating cast bullet using the metal scrap that jewelers use. This brought out voids all over the bullet.

If the void is on a side, this would really aggravate an over stabilized bullet.

I ran ito this shooting .44s in a 1-20 twist custom Marlin that I built.

Just my HO./beagle

[Doble Troble]

Precession makes sense to me. Forces reach an equilibrium. Overloading one force destabilizes a system.

I think you're right about lead being a cohesive metal - but this cohesive property must let go at some point if the centrifuge spins too fast. The real world example is thin jacketed bullets flying apart leaving a fast twist barrel at high velocity. Its not the copper pulling it apart, because you can overcome the problem by making the jacket thicker.

So clearly lead bullets can, and do fly apart. From this it seems reasonable to suppose that they can also be driven to "almost but not quite" fly apart and deform. Of course such deformation will influence trajectory.

[Marlin Junky]

Maven,
If I remember right, it is called precession. Basically, go back to when you were a kid and spinning tops. When you first spin a top, it will wander around a central point. After a few seconds of slowing down, it will stablize and stay in one place. A few seconds later, it will slow down even more and go unstable. I supposed if you were on the border line of over stablization, you could get a tighter group at a farther distance than a shorter one.

That is not an illustration of "over-stabilization" When the top hits the ground, what do you suppose the probability is, of its axis being normal (perpendicular) to the ground?

MJ

[runfiverun]

if you are pushing it fast enough to strip the rifling then wow can it be stabilizing
if its going forward so fast that it won't grab the rifling it can not be spinning to its full
rpm's

[Buckshot]

................There is no 'Over Stabilized' state. The bullet is stable or it isn't. However, there is 'Over Spun'.

................Buckshot

[Larry Gibson]

Maven

"how does excessive RPM result in poor accuracy? I.e., are you suggesting that excessive RPM's magnify bullet imperfections to such a degree that they fly erratically?* "

You've answered your own question.

Buckshot is correct, it is "over spun".

There is a certain level of RPM that causes imperfections in cast bullets to really adversely effect accuracy. Since there are other variables involved this level is more of a threshold than a set figure of RPM. My experience is with a normal designed cast bullet that the threshold is 125-140,000 RPM. This can be bumped a little with some designs, good castings, proper alloy, medium or slow powders, etc but not by much. While "good" (a term relevent only to the user's own definition of "good") accuracy can be had at higher velocity than the RPM threshold it is not always easy to achieve. Also accuracy will invariably be better in or below the RPM threshold.

Larry Gibson

[45 2.1]

All, mto7464 used 58gr. WC 860 in his K-31 and got miserable accuracy. Larry Gibson & Junior think the problem is excessive rotation, ~2,200fps by Junior's calculation. BA Bore disagrees. BABore is correct also..........

Here's what I understand: (1) UNDER rotation results in an unstable CB trajectory and poor accuracy. (2) Lead (and wheel weights) is a cohesive metal, i.e., it doesn't fly apart when rotating rapidly...I think. Ergo, excessive RPM shouldn't pull the bullet apart in flight. Correct so far...(3) The K-31, with its 1:10.3 twist is a superbly accurate rifle with both jacketed and cast bullets, but there's a limit to how fast you can push CB's with it. 58grs. WC 860 strikes me as excessive and likely to produce bore leading with the attendant poor accuracy unless the CB's are very hard (heat-treated WW's, sized prior to heat-treatment). The problem with the powder is that it is not being ignited properly and doesn't burn consistently because of it. Just because a boolit is hard doesn't mean it won't lead. Alloying a boolit properly for toughness isn't practised here much. If you did so, your eyes would light up with the possibilities you would see. Fitting a boolit to the firearm assures that missalignment, caused by ignition, doesn't deform to the point it causes problems with accuracy. Load balancing gives you accuracy with properly fitted and alloyed boolits.

Here's what I don't understand: (1) How can a concentric (via sizer and/or rifle bore) CB be "overstabilized" or over-rotated? By imbalanced loading.(2) Other than a CB stripping or tripping the rifling, how does excessive RPM result in poor accuracy? I.e., are you suggesting that excessive RPM's magnify bullet imperfections to such a degree that they fly erratically?* It can if not fitted. If it is booted it the a** and missaligns, it won't shoot. (3) How do we know the poor accuracy is due to excessive RPM and not poor CB fit fit is correct, poor CB design, excessive pressure for a given BHN, or any combination of and interaction between these? (4) Is there direct evidence of this or are we inferring this? There is a lot of direct evidence, its just not published. Several people here know these facts, but don't post about them.

Larry posted this: Also accuracy will invariably be better in or below the RPM threshold. Prove it. You will have a hard time even getting something close to the challange below. Sink or swim time Larry.

BABore has posted several groups in the past, as have I. Lets see if anyone can match them, let alone at the velocities they were shot at.

I'd appreciate hearing your thoughts on the matter as I'm just not getting it. Thanks in advance for your insights!


*I understand this, but the question is how erratic for a given amount of rotation?

[VTDW]

The only drawback to rpm's in my mind, small as it is, seems to be the boolit encountering an unscheduled disassembly in flight. I just shot some loads at over 2,950 fps this weekend. They showed great accuracy and no leading. I only shot 20 rounds though and from a Marlin MG barrel.

Dave

http://img.photobucket.com/albums/v354/vtdw1/Silly%20Stuff/image5.jpg

[Bass Ackward]

The real world example is thin jacketed bullets flying apart leaving a fast twist barrel at high velocity. Its not the copper pulling it apart, because you can overcome the problem by making the jacket thicker.



DT,

You can also over come this by using a light oil on the bullet as we were continuously beaten by a guy who did that very thing. So .... is the bullet being ripped up by RPMs or is it being destroyed in the bore where RPMs and wind resistance then tear it up upon exit?


Guys who played with tops,

Guys that played with tops when you were a kid, you found that you could pump hard and have it destabilize until it settled in. But what you should have also noticed was that different people could make it stabilize at higher rotation speeds by how the force was exerted.

If you were an only child, then you saw that if you pumped it wildly and rapidly that it wobbled more and didn't stabilize until a lower RPM. But if you built the RPMs up slowly it would be more stable right from the get go and spin better longer. The trick was in your release.

Your gun is your hand. The same EXACT principals apply.

Your muzzle pressure and base squareness at exit determines the wobble. So since we all do things differently, and because our guns are all at different levels, we are all going to see different RPM thresholds that aren't really. But is that the fault of the RPMs? Or what we did in how we launched it?

Very clearly, if you want the complete freedom to do anything you want, launch any ol bullet design you want, any way you want to do it, then the " easiest accuracy " will happen for you at what is thought to be cast velocity levels. The top spins the best no matter how (abused or silly) you pumped it.


Paul,

SO how we design our top, how we mold our top, how hard we make our top to stand up to our force, how violent we build our RPMs for that top understanding our top does have a structural limit, and even the quality of the launching system to help us get a good release, will determine our .... best efforts.

IF our top has a blunt front end, and we KNOW it's going to wobble when it comes out, the more blunt the end, the more wind is going to have an effect on it until it DOES go to sleep. The more the effect, the farther off coarse it will go. We learned this playing with our hand outside the car while dad was driving down the road.

It all works together.


All,

So if we launch it badly and our top is designed poorly to spin in air, the slower you are going to have to spin it if you want to see that pretty spiral travel on coarse. Remember, a slow spin doesn't guarantee accuracy either, but we over look that fact because there there is always a (logical to us)reason for failure at that level.

When you want to learn how to spin that top faster you can take steps to do that. IT ain't hard. But your gun has to have or you have to force the conditions to allow you to do it. A low rifling height or worn muzzle will have a lower top end than ideal conditions have. The better the throat to start it off straight (balanced) in the bore, the better. Especially if one has taller rifling that can hold the bullet straight in the bore under pressure with that terrible barrier to forward travel we have called twist rate.

Or you can say I ain't interested in doing all that and play at the low speed level where it works for an abundance of people. If you don't have the launcher, you got no choice anyway. Just remember, (key point) that even at those.... easiest accuracy .... levels, some people, some guns, some bullet designs spin things straighter than others do too. Same logic applies as you go faster. Only pressure creates more wobble and the wind takes it farther off coarse the faster you make the wind. What it really amounts to is the your margin for error is less the faster you want to go. Or the wider the meplat you want to run. Same as your hand when dad sped up the car.

[44man]

Some excellent points made that I agree with. But since I no longer have any rifles to speak of with proper twist rates except my Swede with it's pitted bore that I have never tried cast in, it is hard to discuss them.
The one thing that has given me trouble with some revolvers has been under stabilization, never over. My single shot pistols were all made with fast twists and have never been a problem.
My BFR revolvers have fast twists, the 45-70 is 1 in 14", the .475 is 1 in 15". Now granted, I can't get the high velocities attained in a rifle to see any sign of "over spun", what I do see is the guns will shoot any darn boolit I can stuff in them with super accuracy and no work at all to find it. And boolits are stable to 500 meters.
Most BPCR shooters like a faster then normal twist. I feel borderline with a 1 in 18" and see boolits that shoot 1-1/2" groups at 200 meters just fall apart beyond that.
My humble opinion is I would rather have a fast twist because if any problem arises it is so easy to just back down a load.
Too slow a twist sometimes makes it impossible to up the velocity high enough for stability.
Even back in my long range varmint hunting days, the very worst rifles to get accuracy from had twist rates too slow for the long range bullets.
If I am going to shoot long range I want spin, not the top that starts to wobble as it slows down. If the cartridge is at it's pressure limits and the twist is still too slow you are :killingpc[smilie=b:.
My most accurate long range varmint rifle would not shoot any group under 1" at 100 yd's but shot several 5 shot 1/4" groups at 350 yd's. That bullet was SPINNING! :Fire: Hit a crow at 400 yd's and just wings fell out of the tree, talk about explosive.
If I hit a blade of grass in front of a target I would spray the paper with shrapnel.
Give me a fast twist any day, I can work with it.

[Maven]

I just got home from the gym and shoveling some snow and read your replies, which I'm happy to say, have helped me grasp the concept. I like the spinning top analogy and thought of another after I posted last evening: Dynamic tire balancing (has something to do with WW's of course). An imbalanced tire won't be noticed at low RPM (mph), but will most assuredly make its presence felt as RPM increases. CB's should thus display the same tendencies, especially as the distance to target increases, correct? (By George I think he's got it!)

As for the slow burning milsurp powders, e.g., WC 860, WC 872, and IMR 5010, I've never had a problem with the first and last named ones with respect to leading and/or accuracy in any appropriate cartridge, i.e., those ~53mm - 63mm long and nominally .30cal. as long as I used heavier CB's (~175gr. or more), LR mag. primers and (gasp!) a small amount of cereal or poly- filler. Btw, I'm going to retest the cereal filler (bran) with 860 in the near future because I'm not happy with the amount of unburned powder left in the bore.

[sundog]

Crankshaft balancer.

I'm following this thread since it started, and all I've been thinking about is weighing boolits, and culling those what don't fit the norm, mainly the light weights. VOIDS. Might look good, but it's got a bubble or piece of trash in it, and guaranteed it will NOT be evenly distributed on the axis. I think Felix said something about a 'spinner' awhile back....

Everything else, bbl condition, twist, powder, boolit hardness and toughness, ... everything else, has a direct affect, but if the boolit is not stable to begin with, well....

So, given any set of parameters you have at hand, whatever they are, that particular set of parameters will dictate the most accurate load. The velocity (rpm) is a by product, not the main event. Just keep increasing velocity (rpm) until accuracy goes south. Need more speed? Gotta change something in your set of parameters, which may or may not be twist (rpm).

If you have an out of whack boolit, then it doesn't make a hill of beans about anything else.

[44man]

You really have to slow down and cast perfect boolits instead of making too many, too fast that might have defects.
The ability to make lead perform in the mold is of the utmost importance and there is no excuse to have voids in boolits. I have stated many times that 10 perfect boolits beats 1000 with defects. A perfectly cast boolit can be spun up to unreal spin rates.
I also keep hearing about the weight of lead in the pot of a bottom pour or in the ladle needs to be the same for every pour. Let me see now, molten lead is a liquid, is it not? I understand that a liquid can not be compressed. As long as the air escapes and enough lead is supplied to fill the mold as it hardens, How can adding more weight make the boolit fill more?
Now dribbling lead into a mold by making it swirl around before it enters CAN cause trouble because you are not forcing out air with weight, plus some of that lead is starting to set up. I can picture layers of lead building up to make a boolit. Might look nice, but what is inside? In my opinion, the boolit must be kept molten as long as possible and more molten lead fed to it as it hardens. Just having a big sprue does not make a perfect boolit.
Pouring molten lead into a mold from a heighth and continuing the pour until the boolit gets all it needs does work but it sure makes a mess as lead pours all around and off the mold. Plus the lead and mold must be very hot. This is hard to do with a 6 cavity mold because lead gets into other cavities and sets up. Just dragging the 6 cavity under a stream of lead until each is filled does not feed molten lead to each boolit as it sets up.
If boolits have air bubbles and voids that cause imbalance with high rates of spin maybe casting technique should be investigated.
There should be no difference between a well cast boolit and a swaged one.
The jacketed bullets that come apart too easy have very thin jackets and soft, pure lead cores. Make the core hard and they will spin up without a problem.

[sundog]

Is there any guarantee that a swaged boolit will be perfect?

My casting technique is pretty good. I've had a little bit of practice in the last 35 years, but occasionally, I pour a boolit that is not up to par - for whatever reason. Just occasionally, mind you. Since I am a hobbiest, the most efficient way I have to deal with that is my electronic scale. Presumably, the ones in the density population of a bell curve are more normal than the others.

I'm not sure it makes any difference how we get the 'near perfect' boolit anyway, as long as we get it. Point is, a GOOD boolit will tolerate more stress, that is, it can be more forgiving of the other parameters, and presumably give us a chance at better accuracy. Or, think of it as a compliment to the other parameters.

[leftiye]

Sundog -
Yes, swaged bullets are pressed into a form with enough pressure to make the metal flow. The formm (die) is completely filled. They are also guaranteed to be dead soft (and lead). That's why they swage them inside jackets.

44 Man, I completely like your approach to casting boolits and shooting same. The fly in the ointment as concerns swirling lead around in a mold, or bottom pouring with the mold against the spout, or any other variations is how fast the lead freezes. Also other variations involving the fact that it doesn't all freeze at once. Voids will happen if you give them any chance at all. My best guess is that that's why moderately frosted is better. The outside of the boolit doesn't freeze instantly in a hot enough mold. This allows gasses to escape, and the lead to freeze homogenously (sp?) and progressively from the outside in, while at the same time drawing more metal from the sprue to completely fill the mold.

Sundog is right, If you don't keep out of balance boolit making to a minimum, (not make voids), you're wasting your time. May as well not do it (cast). This is why velocities and RPMs exhibit " barriers" to accuracy. Ya gotta shoot a good boolit, and not mess it up (at all!) with too fast of powders, too much pressure, gas cutting, poorly fitting boolits, crappy lubes, leading etc., etc., or you're probly not going to enjoy much accuracy.

Obviously, the RPM or velocity "barriers" to accuracy are going to yield to this approach as long as you aren't shooting fast enough that the strength of the lead fails to hold together, or the friction with the air causes grey vapor trails.

[44man]

That is why I like a little more heat and hold the ladle on the mold for enough time to make sure the mold can't take in any more lead. It helps keep the boolit molten longer too.
It is not hard to make a reject or one with a hidden flaw but then again it is not hard to make a good boolit either.
I think one of the biggest problems I have seen is a pot with a bad thermostat that cycles too slow or just doesn't get the lead hot enough. My friend has 3 fairly new pots and he can't make a decent boolit to save his life.
My 1961 Lyman started that. I was casting pretty good and had to stop for a few minutes. I went to take out the ladle and it was froze in hard lead. I had to remove the thermo and make a voltage controller for it. The lady at Lyman laughed when I asked about a new thermostat! :mrgreen: So far my Lee 20# has worked perfectly.
It only takes 80 to 82 volts to hold a pot of lead at a perfect, even temperature. You can use it on any pot, just turn the thermo to max and plug it into the controller. Need a voltmeter to set it. You need a 1000 watt variable light switch and an outlet in a box. Use heavy wire. Plug it in and plug the pot into the outlet in the box.
One caution, the switch has a large metal plate on top. Don't cut any off, it is a heat sink. I had to cut one side a little to fit next to the outlet so I made another piece of aluminum to bolt to it and hung it over the other side.

[Buckshot]

..............I don't know if this has any bearing on anything being discussed here or not. However it DOES have something to do with balance, and maybe harmonics, or maybe the season of the year?

Anyway, the other day I finally got up the gumption to put a couple new wheels on the bench grinder. The 2 that wore out were the ones that came with it a couple years ago. I thought I'd check the balance, so first with no wheels I checked the motor itself and it always stopped smoothly but always in a different spot and just slowly spinning it by hand had it do the same. I figured it was balanced as well as needed.

Doing the coarse wheel next, it had a heavy section, and after dressing it with a diamond it was better but the heavy side would still tend to rotate toward the bottom when stopping, but it wouldn't always rotate straight down or even close to it sometimes. The fine wheel was pretty good as after dressing it really didn't seem to have a 'Favorite ' stopping place, so I just installed it.

When I started it it was REALLY quiet. It was quiet enough before, but now you could hear the wheels accelerating through the air. I was standing there being proud of myself when a faint buzzing started, got louder and then I could hear a couple things vibrateing on the bench. As fast as this happened, it faded away even faster. When I turned it off as it ran down (and it takes forever to stop!) it now has a short mild vibration event.

Does it everytime starting and stopping. But it still runs a LOT quieter overall then before so I'm not gonna mess with it.

................Buckshot

[charger 1]

.


Here's what I don't understand: (1) How can a concentric (via sizer and/or rifle bore) CB be "overstabilized" or over-rotated?



It cant be. If your casting a well fitted to bore, concentric boolit it can spin like crazy. What to fast a twist can do though along with other factors such as poor powder selection, poor throat fit, long jump to rifling is bung up your boolit to where as accuracy falls

To magnify it. lets just say a hypothetical 1 in 3 twist exists. Your boolit has to jump 2 tenths of an inch to get to it, and although your load only does 1500 fps it gets there with a wee charge of super fast pistol powder. In this hypothetical situation your twist has effected accuracy hasnt it?

I've come to the conclusion that if your load is of proper size for throat, your boolit hard enough, and charge is such in case that it creates an immediate push into rifling, any factory twist can be shot accurately....Oh with concentric boolit:-D

[joeb33050]

This has been thrashed about several times, I started the thread once, and I don't know any more after reading all the posts than before reading any.
Some folks believe that RPMs above the threshold decrease accuracy, others don't.
We have theories and discussions about tops and precession and out-of-balance bullets and on and on.
We've got some folks getting downright nasty and cynical.
We're painfully short of experimental data.

We know that:
Some BR and CBA guys are going toward slow twist short/light bullet guns, searching for accuracy.(Although I have wondered if the CBA guys thought this through.)
Twist and MV and RPM are mathematically linked such that knowing any 2 we know the third. You can't get more RPMs from a given gun without getting more MV. Both MV and RPMs go up, and we know that it gets harder to be accurate as MV goes up, beyond ???? fps.
So, is it the MV or RPMs that hurt accuracy?
An experiment or some good data is needed.
It seems to me that the 30 caliber 10" and 12" twists offer an opportunjity for experiment.

The question of lead bullets "blowing up" or deforming because of high RPMs is easily answered by a competent calculator. We know the tensile strength of lead and alloys, and while there is no such thing as centrifugal force, we do have centripetal force, and the calculation should be easy for the competent engineer or physicist. If none offer, I'll give it a try-that's to be avoided.

I have experimental data on a 12" twist 30 caliber rifle shooting very hard 166.1 grain 31141 bullets that were tipping going through the paper at 100 yards-at 1500 fps.
If we took 12" and 10" twist rifles and developed loads with short bullets (100-120 gr.) and increased the MV, then we ought to see accuracy fall apart with the 10" twist while the 12" twist accuracy remained about constant. IF IT'S THE RPMs!!!!!

So, we've got a computation to make to answer one question, and the beginning of an experiment protocol that's do-able and that should answer the question.

We need a mold for a light 30 caliber bullet and some willing experimenters.

Or we can continue theorizing about the incomprehensible.

Anybody?
joe b.

[45 2.1]

Or we can continue theorizing about the incomprehensible. Anybody? joe b.

Some folks let what they do know get in the way of learning anything also. A lot of folks do that in fact............:confused: There are more factors involved than what you think. Incomprehensible, Hardly, and no, i'm not going to write anything more than what i've promised to about it either. Try this thread out also: http://castboolits.gunloads.com/showthread.php?t=26701&page=2

[44man]

For sure, buggering the boolit or getting a crooked start or off center start is more likely worse then a tiny air pocket.
Boolit length is very important to the rate of twist. I had a TC contender in 30-30 years ago that I could hit a nickel with at 100 yd's. I left off the gas check to save money and every single one would go through the paper sideways at 50 yd's. You would not think that 1/16" loss of drive band would throw the boolit sideways. Some would call it wrong and say the boolit was spinning too fast. Kind of hard to do with a 10" TC!
Boolit shape, length and form can cause all kinds of funny things to happen so we can't blame any one thing like spin on what goes wrong. Even a brittle lube that breaks out of one side of a boolit is death to accuracy.
There are no generalizations when using cast boolits. If a boolit doesn't work, nothing you do will correct it except another gun.

[MT Gianni]

..............I don't know if this has any bearing on anything being discussed here or not. However it DOES have something to do with balance, and maybe harmonics, or maybe the season of the year?

Anyway, the other day I finally got up the gumption to put a couple new wheels on the bench grinder. The 2 that wore out were the ones that came with it a couple years ago. I thought I'd check the balance, so first with no wheels I checked the motor itself and it always stopped smoothly but always in a different spot and just slowly spinning it by hand had it do the same. I figured it was balanced as well as needed.

Doing the coarse wheel next, it had a heavy section, and after dressing it with a diamond it was better but the heavy side would still tend to rotate toward the bottom when stopping, but it wouldn't always rotate straight down or even close to it sometimes. The fine wheel was pretty good as after dressing it really didn't seem to have a 'Favorite ' stopping place, so I just installed it.

When I started it it was REALLY quiet. It was quiet enough before, but now you could hear the wheels accelerating through the air. I was standing there being proud of myself when a faint buzzing started, got louder and then I could hear a couple things vibrateing on the bench. As fast as this happened, it faded away even faster. When I turned it off as it ran down (and it takes forever to stop!) it now has a short mild vibration event.

Does it everytime starting and stopping. But it still runs a LOT quieter overall then before so I'm not gonna mess with it.

................Buckshot

I've probably told this before but at the age of 6 I was on the shop steps watching dad swap wheels on the grinder. When it came up to speed he touched his chisel to it and the gronding wheel exploded with one good size piece hitting him in the forehead and he went down like a ton of bricks. It may have been moisture but Northern Utah is pretty dry, it could have been a flaw in the wheel. I though he was dead. He spent the afternoon making a better shield for the grinder which I am sure was homemade from an old motor.
Be careful with new wheels and grinder vibrations. Gianni

[Larry Gibson]

45 2.1
"Here's what I don't understand: (1) How can a concentric (via sizer and/or rifle bore) CB be "overstabilized" or over-rotated? By imbalanced loading.(2) Other than a CB stripping or tripping the rifling, how does excessive RPM result in poor accuracy? I.e., are you suggesting that excessive RPM's magnify bullet imperfections to such a degree that they fly erratically?"

Answer is yes. RPM above the RPM threshold with most cast bullets causes the imperfections to be magnified above that which the stabilization can handle and increased inaccuracy is the result.

"Larry posted this: Also accuracy will invariably be better in or below the RPM threshold."

Time and again it is posted here, on other forums and questioned since cast bullets have been in use that shooters shoot cast bullets at velocities from 200-300 fps on up with excellent accuracy and then accuracy goes south. Their accuracy always goes south at some velocity. When we check by finding out simply what the twist is and then compute the RPM we find accuracy went south in or above the RPM threshold. Some claim to shoot cast bullets with better accuracy above the RPM threshold than below it but I've yet to see proff of that.

"Prove it. You will have a hard time even getting something close to the challange below. Sink or swim time Larry........BABore has posted several groups in the past, as have I. Lets see if anyone can match them, let alone at the velocities they were shot at."

I've offered BABore $5,000 for his 10" twist .338 rifle that he claims shoots 3/8" cast bullet groups at 2400 fps.(172,869 RPM - well above the RPM threshold). All he has to do is sit down with me at a bench and shoot five of those 3/8" 5 shot groups at 100 yards for me. Seems that out to be pretty simple to do. Tell you what; I'll give you $5,000 for any 10" twist rifle you've got that can shoot cast bullets more accurately ar 2400 fps than they shoot them in or under the threshold. Hell, you say you can do it so let' see you swim, I'll pay you for it.

"I'd appreciate hearing your thoughts on the matter as I'm just not getting it."

That is obvious but I'm getting ready to begin a series of tests with three .308 Win rifles; a 10", a 12" and a 14" twist. I will use two or three cast bullets and use loads that start below the RPM threshol;d and go up through 24-2500 fps which is well above the threshold. I will use medium and slow powders and various hardness of alloys. I also will varry the bedding to to keep Bass happy. I also will have the 10" and 14" twist rifles hooked to an Oehler M43 so we won't be guessing about pressures, velocities or BCs. We will see where accuracy goes south. Sometime in the future I will do the same with 9", 12" and 14" twist rifles of .223 cartridge.

Larry Gibson

[leftiye]

Buckshot, Sounds like a rpm specific balance problem? Maybe a lot like the one Maven mentioned in his tire balancing post.

44Man.... My favorite invention is the mold heater. I made mine out of one of those small Lee lead furnaces, but I understand an adjustable hotplate and a steel trivet with a can upside down on top with a door cut in the side will work fine (wonder where I heard that).. It's not lead temp but mold temp that really (I mean REALLY) matters. If you heat the mold up to just shy of detructive frosting, and use the coolest lead that won't freeze up in the spout, I think that's the formula. And yes that can be lead that's below 600 degrees.

[leftiye]

Buckshot, Sounds like a rpm specific balance problem? Maybe a lot like the one Maven mentioned in his tire balancing post.

44Man.... My favorite invention is the mold heater. I made mine out of one of those small Lee lead furnaces, but I understand an adjustable hotplate and a steel trivet with a can upside down on top with a door cut in the side will work fine (wonder where I heard that)..

It's not lead temp but mold temp that really (I mean REALLY) matters. If you heat the mold up to just shy of detructive frosting, and use the coolest lead that won't freeze up in the spout (use a thermometer to monitor lead temperature!), I think that's the formula. And yes that can be lead that's below 600 degrees. One a them IR thermometers will allow you to determine what mold temperature is optimum. I find that 327 degrees vicinity is good.

[runfiverun]

larry
i hope that you post as you go along!

[45 2.1]

I've offered BABore $5,000 for his 10" twist .338 rifle that he claims shoots 3/8" cast bullet groups at 2400 fps.(172,869 RPM - well above the RPM threshold). All he has to do is sit down with me at a bench and shoot five of those 3/8" 5 shot groups at 100 yards for me. Seems that out to be pretty simple to do. Tell you what; I'll give you $5,000 for any 10" twist rifle you've got that can shoot cast bullets more accurately ar 2400 fps than they shoot them in or under the threshold. Hell, you say you can do it so let' see you swim, I'll pay you for it. I don't sell accurate rifles, especially when i've put the time into getting there. If your wad of money is burning a hole in your pocket, duplicate BABore's rifle. I really doubt he would invite you to his place to shoot or watch him shoot either. To bad you won't put the time into learning how it's done, you just want to buy the results. As far as your tests, i'm sure that you'll make them turn out where you want them to.

[joeb33050]

I don't sell accurate rifles, especially when i've put the time into getting there. If your wad of money is burning a hole in your pocket, duplicate BABore's rifle. I really doubt he would invite you to his place to shoot or watch him shoot either. To bad you won't put the time into learning how it's done, you just want to buy the results. As far as your tests, i'm sure that you'll make them turn out where you want them to.[/B]

Do we need this kind of comment?
Maybe old 45 2.1 needs some relief, I think he may be having a backup.
I'll be happy to chip in $10, just send me your address, 45, and we'll help you get back to normal.
joe b.

[45 2.1]

Do we need this kind of comment? With swearing going on elsewhere (especially from someone who should know better, this is a family forum as 45nut and other moderators have stated, several times), I don't think this is out of line.
Maybe old 45 2.1 needs some relief, I think he may be having a backup. Some of the things you've put out haven't been well received either, Joe. I could say a lot more, but won't at this time.
I'll be happy to chip in $10, just send me your address, 45, and we'll help you get back to normal. If you got money burning a hole in your pocket like brother Larry, send it to 45nut, he is need more than most here. Maybe ole Larry could buy one of 45nut's guns for the $5,000 and really help him out.

[Bass Ackward]

I also will varry the bedding to to keep Bass happy. Larry Gibson


Larry,

Work the load first to keep you happy. :grin: That's the tweaker step. You may not have to play with bedding.

I ran a "what produces the worst accuracy" test for balance and RPM and I used jacketed to remove the cast stigma and the design is somewhat close to normal cast bullets.

I used a dremel and simply cut into the body of of some Speer 165 grain round nose bullets for 30 caliber. I didn't pay any attention to how deep each was so that the weights would be different too. One was 12 grains light. This way, these things would be really out of balance but without a big effect from wind on the nose or pressure on the base.

The second group got the dremel treatment treatment on the base with only a light nick. Now these would be outta balance too, but had no where near as much metal removed so that balance wouldn't have as great of an effect as the others.

These were shot with two loads. 50 grains of 4064 that Quickload predicted 52,000 psi. The low load was 38 grains of 4064 at Quickload predicted 24,000 psi. Understand no accuracy was considered choosing these loads. Just throwing some charges in a case like some guys would do with cast.

Basically, the low velocity load showed little difference in accuracy compared to the high as everything was in the 1 1/2 - 2 inch area. But the high pressure load accuracy went from 1 1/2" with good bullets to just under 2 3/8" for the side outta balanced ones, to 5 1/4" for the base deformed jobs. All holes appeared round on the target.

I was trying to see if RPMs or pressure had the biggest effect on accuracy. So form your own opinion. In this case, pressure won or lost how ever you want to look at it.

And from this test, outta balanced accuracy from RPMs had less effect on accuracy than pressure on a bad base. Clearly, best accuracy for jacketed bullets, defective or not, occurred at low .... pressure / velocity or RPMs. Just like cast.

[4570guy]

My friend and I had this discussion a while back after he had been working up a series of handloads in his AR-15 (with jacketed bullets). His rifle shot fine with successively smaller bullets from 77 gr, 62 gr, 55 gr, etc until he got to some 53 gr bullets I had given him. After shooting these, we could never find a hole in the target. Upon observation, I would see dust puffs kick up at random locations on the berm at 100 yds whenever he would shoot. These bullets were obviously flying wild. This got me to thinking that just like a long bullet being spun too slowly, there was probably an upper spin limit on a short bullet.

I found this figure in a document titled "How Bullets Fly". (Ref http://www.fulton-armory.com/fly/stab.htm). It shows that there is a static, or gyroscopic stability limit for large bullets spun too slowly (i.e., the Greenhill formula addresses this). There is also a dynamic stability limit for bullets spun too rapidly. The green triangle in the middle represents regions of stability.

So, yes, we can spin a small bullet too rapidly resulting in wild shooting. I suspect you will find this dynamic stability limit before reaching the strenght limit of the material unless the bullet is very poorly constructed.

[Larry Gibson]

Bass

My experiments have pretty much indicated the same as yours using jacketed bullets. With cast bullets using medium to slow powders I believe the same is also true. It is my contention that the RPM adversely effects accuracy of the bullet above the threshold to a certain point. At that point the base is also deformed by too much pressure and we see a really radical loss of accuracy. This is just as you saw with jacketed bullets. It happens when accuracy (above the RPM threshold) with a cast bullet goes from 3-5" groups (100 yards) to 8"+ or even off the paper.

Some believe the cast bullets come apart or have skipped over the rifleing. I do not think that as I have recovered such bullets and there is no indication of the bullets coming apart (see note below) or that the bullet skipped over the rifling. The bullets were, however, seriously deformed from obvious setback during acceleration and the bases were deformed and uneven. The rifling on these bullets was strong and showed no indication of stripping or skipping over the rifling.

I think we are pretty much on the same page here on cause and effects. We seem to disagree on when it happens to cast bullets is all.

Note; I am well aware of jacketed bullets disintegrating in flight from too high RPM as I have observed it many times. This happens at much higher RPM and velocity than we're talking about here with cast bullets.

Larry Gibson

[Larry Gibson]

45 2.1

BABore can turn down the offer for whatever reason he wishes. However, he made the statements and I made a generous offer. Whether he sells the rifle or not is ok but not wanting to sit down and shoot with someone to demonstrate his claims reminds me of an old Army saying; "The max effective range of an excuse is zero meters." I will sit down with anyone and show them (they can watch me shoot all they want) what I claim.

As to my "put(ing) the time into learning how it's done" you know I have put the time in and I do know. That is why I question the claim. You and I have had extensive PMs on your methods to achieve said accuracy at HV (high RPMs). I have tried your methods (nothing I have not tried before many times before and use several of them) and have not had better accuracy at HV tha in or below the RPM threshold. I have tried Bass's methods with the same results; accuracy is better in or below the RPM threshold. I don't believe you have any better or as good accuracy above the threshold either. Reasonable accuracy can be had above the threshold if one does use many techniques that you, Bass and others use (me included). But getting "reasonable" accuracy does not answer the question that always brings this subject up; i.e. a poster ask a question like "how come I get 2" groups out of a 311291 in my '06 at 1800 fps but can only get 3-4" groups at 2100 fps or 5" groups at 2400 fps? Too much RPM is the answer.

The point is; accuracy will be best in or below the RPM threshold for any cast bullet.

Larry Gibson

[45 2.1]

reminds me of an old Army saying; "The max efective range of an excuse is zero meters." This isn't the army, perhaps you shouldn't have retired.

As to my "put(ing) the time into learning how it's done" you know I have put the time in and I do know. that really isn't apparent from what you say. That is why I question the claim. You and I have had extensive PMs Extensive...Hardly, nothing could be further from the truth. on your methods to achieve said accuracy at HV

[Larry Gibson]

45 2.1

Whatever, I choose to have a sensible discusion not an arguement.

Larry Gibson

[sundog]

leftiye, back to the swage boolit thing. If there's an imperfection in the material prior, there will be an imperfection in it after it is swaged. I'm thinking that you can't squeeze an air bubble out of a chuck of lead. Can you?

Larry, exterior ballistics. Sounds like the problem Waksupi was having with the Swede. To much speed (rpm) made them look like bananas. I bet the were straight before they left the bbl.

Increasing velocity will not increase the number of revolutions over a given distance. It will reduce the time needed to traverse the same distance (inverse relationship to velocity), hence higher rpm. It'll still turn the same number of times over an equal distance, regardless of velocity. So, does that make velocity or time the culprit?

[45 2.1]

Sounds like the problem Waksupi was having with the Swede. To much speed (rpm) made them look like bananas. I bet the were straight before they left the bbl.

Waksupi cast those boolits out of Tin, no lead in them at all (at least thats what he told me). So the question is just what does that have to do with a cast boolit of lead? From his test we know a tin boolit doesn't work to well, but we do know one of lead does work to at least 1700 fps with the 6.5 cruise missle. The Swedes also shoot FLGCs that long at much higher velocities. When they first developed the cartridge, they had trouble with their first FLGC bullets doing the same things as bending, blowing up at impact that your seeing with the cruise missle. Remember the original FLGC weight was about 159/160 gr. There problem was one of jacket strength, which they solved. The Swede is also powder finicky. It likes 4350 for heavy FLGCs and little else, of course it shoots under MOA with heavy FLGCs and 4350 too. Might you try something that is a tougher alloy, you might find some success with more velocity.

[Larry Gibson]

Larry, exterior ballistics. Sounds like the problem Waksupi was having with the Swede. To much speed (rpm) made them look like bananas. I bet the were straight before they left the bbl.

Increasing velocity will not increase the number of revolutions over a given distance. It will reduce the time needed to traverse the same distance (inverse relationship to velocity), hence higher rpm. It'll still turn the same number of times over an equal distance, regardless of velocity. So, does that make velocity or time the culprit?

RPM stands for Revolutions Per Minute (I know you knew but just making the point here) which means it is based on time. In this case the time traveled. Hence as you say the higher the velocity the higher the RPM given the same twist. Actually both velocity and time are culpable but since velocity reduces the time I'd say it's the leader of the pack. The other contributing factors given a cast bullet of appropriate weight and quality of cast which fits the throat are the time pressure curve (caused by the burning rate of powder used) which is usually referenced as accelleration, bullet design, alloy, hardness of the bullet, lube and fit of GC to base (solid and square). Since all cast bullets are deformed in some way when fired how much deformation drives how far into the RPM threshold you can push before the adverse effect of RPM overcomes rotational stability and accuracy decreases.

Bass, in particular, has found a bullet design, pays close attention to these other factors and is able to shoot pretty respectable groups in the 24-2500 fps range with a 10" twist '06. My tests (using his bullets, methods and loads) show the same good accuracy at that HV. However that bullet still is more accurate in that same rifle in the RPM threshold. What happens is that the accelleration causes less defect with that design of bullet with the HV loads used. Thus the higher RPM of the less defective bullet does not effect the rotational stability to as great a degree as it does with other bullet designs that would sustain more defects with the same load. The less defects the bullet sustains during accellertaion (internal ballistics) the less it is out of balance and is adversely effected during flight (external ballistics) by RPM. But again the point being is that that bullet is still more accurate when fired with in the RPM threshold.

Larry Gibson

[44man]

This is from a letter I recieved from Omark Industries long ago and I quote;
"For a 1 in 10" twist your bullet will revolve once in every 10" of travel. At 1000 fps it will revolve 1200 times per second at 72,000 rpm's.
At 3000 fps it will be 216,000 rpm's.
The rpm's of your bullet will not increase once it is free of the barrel and no more force is applied to it and it's velocity does not increase."
From this, I see that the rpm's increase with increased velocity WHILE STILL IN THE BORE.
If you are over spinning your boolit, reduce the velocity.
I have to ask, how do you determine if the bullet is spun to fast? Does it shoot bad at close range? Does it go to sleep at long distance and shoot tighter way downrange?
You might say it tumbles but don't slow spin rates do this more then fast as long as the bullet doesn't hit something?
Are you shooting just over the speed of sound with a slow twist so the bullet goes through the subsonic transition with too little spin for stability?
Have any of you shot a long bullet from a smoothbore to watch the fun?
There is no way to put a dead solid pat answer to this question. Every single thing you do or use has an effect, good or bad.
How does a boolit look like a banana after it leaves the bore unless it travels downrange and HITS something? I found a lot of bent boolits on the range but none stopped in midair and fell to the ground. I also found a lot of straight boolits from the same gun.
I will only believe bent boolits at the muzzle when I see a stop action picture of it.

[Ricochet]

Sounds like the problem Waksupi was having with the Swede. To much speed (rpm) made them look like bananas. I bet the were straight before they left the bbl.I bet they were also straight in flight, before they hit the snowbank. I've seen many recovered bullets and boolits that have bent when they tumbled sideways in a fluid medium, but can't understand how spinning them too fast could cause them to bend in that manner. Yawing, sure, but bent? I doubt it.

[Larry Gibson]

Depends on how "bent" he meant the bullet was. I've recovered bore riding bullets where the nose was bent to one side but it happens in the bore during accelleration when the nose is unsupprted. You can tell the bullet was bent in the bore as there is rifling marks on one side of the nose. Others report the same thing.

Larry Gibson

[Larry Gibson]

Every one wants to post an anallogy so I shall also. Ever drive a car with an unbalanced tire? Notice that you can attain a certain speed with the tire rotating without vibration? Then at a certain speed the tire will begin to vibrate badly? The faster you try to go the more the tire wobbles and vibrates? It is because up to a certain speed the tire maintains rotational stability. Then at a higher speed with attendant higher RPM the RPM overcomes the rotational stability and the tire vibrates and wobbles.

Same with a cast bullet in flight. The more balanced the bullet is (less defects from obturation and acceleration) the less the wobble above rotational stability. The area where the rotational stability of a cast bullet is in the RPM threshold, i.e. 125-140,000 RPM.

Larry Gibson

[leftiye]

Sundog - The way I hear it, yes the voids are collapsed and are left with no volume. (haven't had the opportinity, nor the means to prove it for myself, but......) The key is pressures that will flow the (pure) lead. That is, if the die has a bleed hole the lead will extrude out of it for as long as the pressure exists. This is the method that is used to get exactly same weight bullets with all lead bullets. The same applies to jacketed if and only if the jackets weigh the same. When using lead wire though there should be no voids as this is manufactured by extrusion (through a "bleed hole" if you will) in the first place.

[leftiye]

Larry, I think you are right. By and large groups do suffer more due to out of balanced boolits at higher velocities, and/or RPMs. I think everyone here agrees on that. I suspect that, as you've described, at some point it goes all to h@!! too. Myself, I don't hear anyone claiming that it doesn't matter, nor that top of the line match grade accuracy can be achieved as a daily matter regardless of speed/rpms, only that in some cases comparably good accuracy has happened at thse velocities/RPMs. Still with the caveat that better accuracy might be accomplished at lower velocities more easily. You've made me aware of yet another factor that affects accuracy, just as boolit fit. hardness, uniform ignition, etc., etc., do.

My favorite thing to argue about is that it is not mere pressure, but the resulting acceleration acting against the inertia of the fore parts of the boolit that causes deformation. Anyone?

[sundog]

chuck a length of wire in a variable speed drill. slowly increase the speed. longer and thinner wire collapses at lower rpm. shorter and thicker withstands more rpm. Would that mean that a slow turning round ball is the most accurate? Or maybe a one caliber DEWC? Onliest problem is they don't fly so good.

leftiye, how many psi do you suppose that would take to squeeze an air bubble out of a piece of lead wire?

[35remington]

I'll volunteer a 200 dollar donation to FLY one of these guys to the other's place so we can see the shooting verified.

Or not.

There is often a bunch of invective passed from place to place in these posts, but very little light.

I don't care who has to 'fess up, but constantly rehashing the same points gets a little old.

This is more like the Saturday morning coffee klatsch than any real discussion.

Yeah, this post is a little crabby, but the time has long since passed for a demo and true advancement of the craft. If you guys wanna shoot in Nevada, Kansas or Maine, I don't care which, I'll show up.

I'll even take up a collection here if it gets the job done. I'd think the potential for accolades from the cast bullet shooting fraternity would have made such a demo happen long ago.

Apparently not.

[runfiverun]

in these discussions i never hear anybody mention air pressure on the nose of the boolit
when you break the sound barrier going up and down.
i'm not sure on the #s but isn't 2500 fps near mach-3
thats a lot to ask from a chunk-o-lead
not gonna stop me from trying to get there, but this could have about as much to do
with bullet bending,yawing,etc as rpm's

[felix]

run5run, check the other threads like this in the archives. Especially, look at boolit design threads. ... felix

[44man]

Bent boolits in the bore are caused by offside slump with soft lead when hit with a sudden pressure. The wrong boolit nose design, bore ride can cause it. This is very common with BPCR and the soft, heavy boolits. I heard the Lee 500 gr boolit with the sharp nose is subject to this. Boolits can shorten a lot with the fast pressure rise of black or a fast smokeless. Even the whole nose and bore ride can go into the grooves.
This is not caused by twist or spin but happens right away, maybe even before the boolit leaves the case.
Stand a big, soft boolit on an anvil and smack the nose with a big hammer---same effect. The longer and heavier the boolit, the more inertia it has and a long, unsupported nose can move sideways.
Make the boolit harder and use a slow powder.

[sundog]

35Rem, who specifically are you talking about? Two hunert is a lot of money, yes?

[sundog]

ahhhh, Larry, ROUNDS per minute? Man yer killin' me here. Rounds Per Minute....

whodathunkit?

[Bass Ackward]

Yeah, this post is a little crabby, but the time has long since passed for a demo and true advancement of the craft.


35,

Advancement of the craft? I don't think so. Personal ego? Uh huh. If you read the Lyman Cast bullet manual from the late 50s guys talk of 2700 fps in a few places. Veral Smith wrote about most of his work at full power HV and his first version was from the 60s. The mold I acquired was made by him for someone else during the 70s. This stuff isn't anything new. And I don't treat it as such. And except for how to do HV with softer metals to make cast more effective in hunting applications, it's all covered in his little blue book.

But what these discussions are REALLY about, is the culmination and application of ALL knowledge on this board. Every concept we discuss put together along with the correct problem solving application of that information. Basically, how YOU can think to solve YOUR problem. High velocity ...... or low.

When I problem solve, I never think in terms of RPMs. I can think in terms of alignment and review my processes. I can think in terms of ignition and of delaying and elongating the pressure curve and take steps to solve that. I can think in terms of bullet design and obtain / create a stronger bullet design. Or a more aerodynamic design to cut through wind if that helps.
What is the only thing discussed on this board that supposedly can't be over come? RPMs.

Once the shooter begins to think in terms RPMs, he has stopped trying and accepted defeat. His learning curve just hit the wall. Even if he just considers the possibility, he has already begun to accept defeat. That's the crime.

Not a single soul on this board will tell a person that a 2" group at 50 yards is a bad effort or that RPMs got him. In fact, we hear of flight problems there like keyholing and everyone accepts that there is a correctable solution. But if I shoot 1" or a 1 1/2" at 2800 fps at 100 yards, (sometimes much smaller, but I ain't about to lose even more credibility :grin:) my groups are being destroyed by RPMs? Or they aren't as accurate as I would get at lower velocity? Poppy cock. Maybe I just can't handle the recoil to shoot any better than that? I mean, you don't see many guys shooting benchrest comps with 378 WBY's. But it can be shoot very accurately in a vise! Cartridge problem? Cast bullet problem? Or shooter one?

Do I care if anyone wants to shoot HV? No, free country. Unless you DO want to learn. Then I believe in your right enough that I will enter into these seemingly stagnant barrier discussions to encourage you on. And I will do so tomorrow, next week, month. Personally, I believe that my low velocity understanding and handgun knowledge was GREATLY enhanced when I stepped through that high velocity door. Can't yet figure out why I still shoot some pretty crappy low velocity loads at times. RPMs? :grin:

As to the cranky thing ................... I see you are from Lincoln. There were some pretty heavy personal confrontations in that area, some called Indian wars. My wife is from Hastings. I have a theory it's in the air out there or something. :grin:

[charger 1]

I read all this and I cant help but wonder who's impressing who. I take a boolit that fills the throat and bore taper. Make it of hardness capable of the load pressure. Compress it onto a charge that provides a shove as soon as primer lights and proceed to shoot half moa. I guess if gun barrels were being made where the rifling acted like an obstruction ie 1-4 twist I'd worry. Until then I'll just SIMPLY shoot

[Larry Gibson]

Bent boolits in the bore are caused by offside slump with soft lead when hit with a sudden pressure. The wrong boolit nose design, bore ride can cause it. This is very common with BPCR and the soft, heavy boolits. I heard the Lee 500 gr boolit with the sharp nose is subject to this. Boolits can shorten a lot with the fast pressure rise of black or a fast smokeless. Even the whole nose and bore ride can go into the grooves.
This is not caused by twist or spin but happens right away, maybe even before the boolit leaves the case.
Stand a big, soft boolit on an anvil and smack the nose with a big hammer---same effect. The longer and heavier the boolit, the more inertia it has and a long, unsupported nose can move sideways.
Make the boolit harder and use a slow powder.

44man answers the question quite nicely.

Larry Gibson

[Larry Gibson]

ahhhh, Larry, ROUNDS per minute? Man yer killin' me here. Rounds Per Minute....

whodathunkit?

Doh!......well my initials are LMG so "rounds per minute" may be perenially on my mind......

Thanks for the heads up, it is corrected.

Larry Gibson

[35remington]

Bass, the offer was to fly whomever to the moon, Colorado, or wherever to get the rpm point resolved to somebody's satisfaction.

The point gets obscured in vague doublespeak - as in, "if you don't know, I'm not going to enlighten you."

So, essentially nothing happens.

Advancement of the craft? It most certainly would be, as whatever was written or said in the past isn't common knowledge or the rpm point would be accepted information by now, and there would be nothing to debate. Such hasn't happened.

This is on the fringe of cast bullet information, as many really don't care if their cast bullets approximate centerfire jacketed velocities. Others do but can't get it done so they don't beat their heads against what they perceive to be a barrier to advancement.

Those with personal egos in the issue have already stuck their oar in, and we know who they are.

What I cannot figure is that if the issue has been SO thoroughly resolved to their satisfaction I would think that the opportunity to deliver an ass whuppin' would make their personal egos the size of the Hindenberg if they could pull off what others say can't be done. I don't begrudge a guy with a big ego if he has something to contribute and can clear up contentious issues.

So, therefore, my offer to fly the participants in these more heat than light debates to a common location. Make it an advanced bullet caster's seminar and have others attend if they wish, whatever....I don't care. Just provide an opportunity to make it an advancement of knowledge, not just a repeat of vague generalities. Remember my earlier comment about the topic not being resolved before you take issue with my "vague" comment. It hasn't been resolved here. Time to do so.

This cast bullet board has enough knowledgeable members by now that Ph.D level issues should be methodically and clearly addressed. Egos aside, for once.

Yeah, I know......In a perfect world, or whatever. One can see the frustration of the guys on the CBA forum that post here. At times, they can be annoying and stir the pot. However, their results at matches are there for the world to see. One might think there would be an opportunity here to show those guys (and others of us) some cutting edge info by arranging such a meet.

Due credit would be given to those supplying information that would make this cast boolit hobby take a step forward for all.

[Larry Gibson]

I fly back and forth across the country anyways. I would leap at the chance to meet and shoot with anyone. Yup, I've got an ego as it goes with a type A personality. However I've always prided myself on having an open mind. In this issue I will gladly change my mind if only those who disagree can prove what they say. We've all seen ample proof that RPM above a certain level adversely effects accuracy. I believe even in this thread I've stated that good accuracy is attainable at HV even with high RPM. Thus when Bass talks about "Once the shooter begins to think in terms RPMs, he has stopped trying and accepted defeat. His learning curve just hit the wall. Even if he just considers the possibility, he has already begun to accept defeat. That's the crime" it is he who apparently has closed his mind.

Many of us still strive to push the envelope and find what works and why it works. Conversely along the way we find what doesn't work and why it doesn't work. I've many times here asked, challenged and perhaps pleaded some to demonstrate what they say can be done and to do it repeatably. One random group does not justify proof to me. I've shot too many good groups with a load on one day and not been able to repeat that good group with the same load there after. None have taken me up on any offers (including $5,000 for a rifle not worth 1/5 of that) to show me.

Bass did send me a quanity of his LBT bullet that I tested it in an '06 with 10" twist and a 308 with 14" twist. There is some real potential for that bullet at HV in both twists. But the fact remains the best accuracy I got with that bullet was in the RPM threshold. I got consistant 1-1.5 MOA up through 2500+ fps in my 14" twist Palma rifle. The same bullet out of a 10" twist '06 shot into 1.1 MOA at 1830 fps which is 132,341 RPM; again in the RPM threshold. That was with the same level of accuracy with pretty close to the same RPM of 130,000 RPM which the 14" twist barrel got at 2500+ fps. When velocity was pushed to 2500+ fps in the 10" twist barrel accuracy was 2.5 -3 MOA consistantly with an attendant 180,000+ RPM; a considerable amount above the RPM threshold. Is it really that hard to see the relationship that the increased RPM had on the accuracy of the bullet?

The results of that test with Bass's LBT bullet is typical of every cast bullet I've ever shot in any rifle. Best accuracy will come in or below the RPM threshold and when the cast bullet is pushed above the RPM threshold accuracy decreases. The amount of decreased accuracy is just greater with some designs of cast bullets vs other designs. That LBT bullet is a very good design to resist obturation and deformation during accelaration. Thus there are less defects with it than with a regular cast bullet design for RPM to have an adverse effect on above the RPM threshold. With regular cast bullet designs the decrease in accuracy above the RPM threshold is more pronounced. We have all seen it. Now if Bass, 45 2.1 or any others can get a 311291 to shoot as well out of their 10" twist '06 at 2500 fps as it will at 1800 fps I'd really like to see it. Now 2.5-3 MOA at 2500 fps isn't all that bad and is certainly adequate for deer hunting out to 200 yards but the fact remains that best accuracy was in the RPM threshold.

I am willing to travel, am putting my money where my mouth (or ego) is and am preparing to conduct extensive research on this matter using 10, 12 and 14" twist barrels. I also have a M43 Oehler system so I can measure pressure of the 12 and 14" twist barrels (the M788 precludes me from using the M43 though I may purchase a different rifle for the 10" twist portion of the test). I will also measure the down range velocity of the loads and report on the bullets actual BCs. I will report on this forum the factual results of my tests whether they agree or disagree with my idea's or ego. If necessary I will change my mind if the facts demonstrate I am wrong. That is not ego, that is an open mind.

I would definately like to meet somewhere for a symposium/shoot as 35remington suggests.

Larry Gibson

[35remington]

My point is, I guess, that a seminar from the most knowledgeable contributing members of this board is long overdue.

Hell, I could develop a schedule and a list of presenters off the top of my head, with members I see as most likely to have information that could be best demonstrated rather than posted on an internet message board or by PM's.

We all know that the PM is where the real information exchange on the board occurs, yet no one other than the participants benefit from this.

RPM's? Have the posters here make a round robin discussion, with a shoot at the end to demonstrate pertinent point and proof of their assertions. Ego pumping time, but it's a contentious enough issue that it deserves its own venue.

I'd have Felix give a presentation on lubes and powders.

Buckshot - tooling up to produce casting accessories, and loading for odd calibers.

Bass? Allowing for changing conditions on load development. Anything pushing the envelope, with how to's and similar.

45 2.1? Bullet design, factors that influence accuracy.

Larry G - milsurps and loading for same. Perhaps something on fillers from him as well.

Point being, we're to the level that those here have much to contribute by their presence, and we have much to lose by never meeting these individuals in person or hearing what they have to say. The internet is wonderful in bringing these people together but limited in really being able to disseminate information that is best conveyed in person.

Failing this, some are trying the book format for addressing Ph.D level issues, but these are a long time coming.

The "I can and you can't" threads with supposed proprietary information really don't produce any information that others can use. Thus my claims of stagnancy with the exchange of real knowledge.

Maybe a meeting isn't possible given everyone's schedules, but more "how to" stickies would be appreciated, rather than "every gun is an individual and everything must be custom tailored."

Big whoop. We already knew that. The real information just isn't getting out there, due to either egos or an inability to address pertinent points. It would be a shame to lose that.

[crabo]

This discussion is way out of my league, but I belong to a group of bass players on the internet, who live all across the country. We would meet once a year for a weekend, in different parts of the country. Someone new would host it every year. We would all bring gear and sit and and play each others stuff. Some of us would give clinics on different playing techniques and topics such as music theory. It was a blast and it gave everyone a chance to meet others and see new gear.

I don't know why the same thing couldn't be done here. Someone would need to host the event, where there is access to a range, along with motel accommodations, and it would allow for a chance for some great education and fun. It was also interesting to see that some of the most frequent and opinionated posters couldn't play very well. (of course that would never happen here)

Something to think about.

Crabo

[longbow]

I have been reading this thread with some skepticism regarding the RPM/balance theory, thinking it was more likely the boolit material yielding under the stress due to tremendous RPM's and the pressures required for the higher velocities.

I found the equation to calculate radial stress for a rotating cylinder:

radial stress = [(3+Poisson's ratio)/8] x density x (rotational speed in radians/sec)^2 x (radius)^2

The tangential stress calculation is a little different but since this is a solid cylinder the result is the same. I do not believe this is a combined stress situation but if anyone knows please correct me.

I did some calculations for a .30 cal. boolit since it is pretty commonly used.

I was surprised to find that even lead of only 6000 PSI ultimate strength which would be about 12 BHN will theoretically take 225,000 RPM.

The highest strength hardest lead/antimony alloy I can find (this is published data from a technical manual) is 8% antimony heat treated at 450 degrees F and quenched, resulting in 26.3 BHN after aging one day and has 12,350 PSI ultimate strength. It will take over 300,000 RPM.

Much higher RPM's for both than I had anticipated.

This is theoretical though and doesn't take into account misalignment or stress due to imbalance. Nor does it take into account frictional stresses in the bore or in the air, turbulence, imperfections, uneven obturation, etc. A slight wobble at those RPM's could be enough to cause increased stress and yielding.

Even so I guess I have to accept that it is enough above the 125,000 to 140,000 RPM threshold limit Larry uses to question whether yielding could be the culprit. This may also help explain how some shooters are achieving much higher velocities than normally accepted. If the boolits are well made and concentric and shot out of a good barrel they fit well, the RPM's shouldn't result in boolit yielding - not directly anyway.

So, I guess I haven't added much if anything to the discussion except now you can calculate the stresses in your boolits at whatever RPM you are developing.

I hope you guys do get together and shoot this one out - so to speak. I know I am still looking for an answer.

Longbow

[Larry Gibson]

Longbow

I've not found evidence of the bullet material yielding at any cast bullet RPM I've shot them at. I've also not found evidence of the bullets bending in flight. I have found the little "Q" with 6.5 bullets that has been discussed in the past. I have recovered lots of cast bullets of various types shot into snow that did not impact the ground. Many of them exhibited substantial deformation, uneven bases, bending and setback in the bore from excessive acceleration. I also had limited access to a bullet catcher at a crime lab but mostly caught pistol bullets and cast rifle bullets up to 2000 fps in it. It was using that bullet catcher that I found out how much damage can occur to the bottom end of a cast bullet that is seated below the case neck.

High velocity with cast bullets is not hard to attain. Take a .222/.223/22-250 with a 14" twist for example. Many here cite high velocity loads that are accurate. I do not doubt them as I have also attained good HV loads with those cartridges in 14" twist barrels. I've got very good consitant accuracy of 1 - 1.5 MOA in the 2700-2750 fps range. So why is that not hard to do when I can't get that kind of accuracy with an '06 at that velocity. Well the RPM of the 2750 fps bullet out of the 14" twist is 141,509; the top end of the RPM threshold. I actually always got the best accuracy out of those 3 cartridges in the 25-2600 fps range (128, 644 - 133,790 RPM). Out of the '06 with a 10" twist the RPM at 2750 fps would be 198,079; considerably higher than the RPM threshold which explains why you won't get 1 - 1.5 MOA with a 10" twist '06 using cast bullets at 2750 fps.

Larry Gibson

[44man]

I am glad to have all of you with math knowledge here!
2X2 gives me trouble. :mrgreen:

[78CJ]

Have any of you guys looked at he "How bullets fly tutorial", 4570 posted a link, I did not click on it but I think it is the same one I have seen. It is long but the answer to your question about overstabilization is in there.

I can't believe so many people would bicker over common sense and post hypotheticals without first educating themselves a little. And no, I am not going to try and explain it to you.

Forces and Moments involved in this get confusing quickly.

[Larry Gibson]

78CJ

Thank you for bringing that article up again. I contains some valuable information germain to this discussion. I'm quite familiar with that article. Note the discusion and attendant math are relevent to keeping the bullet stable in flight. There is no discusion on the accuracy of a stable bullets in flight. Simply put you can have accurate AND inaccurate bullets that are still stable in flight. For a quick synopsis of how imbalances adversly effect the accuracy of a stable bullet I would refer you to the discusion in the Hornady 4th edition, volume 1, page 18;

"As long as the bullet is in the barrel it rotates around its center of form but when it leaves the barrel it spins around its center of gravity and this causes it to veer slightly off its intended course at a tangent to the spiral described by its center of gravity when it went up the bore." (you can view the pictures in the manual)

"Less than half a thousandth of an inch error in jacket concentricity can and does have a detrimental effect upon a bullet's course."

Hornady is of course discussing jacketed bullets but the same applies to cast bullets. Now considering the cast bullet has more than .0005" error in concentricity from casting, sizing and obturation to fit the throat/bore and from acceleration than it's jacketed cousing we see there is much more room for a "detrimental effect on a (cast) bullet's course. Increasing the RPM of a cast OR jacketed bullet increases this "detrimental" effect. Also with cast bullets there is that threshold where the RPM overcome the rotational stability and greater inaccuracy occurs. This is what I refer to as the RPM threshold.

Larry Gibson

[78CJ]

I agree that when you have two identical projectiles and one is slightly less concentric then yes that one will experience instability faster than the more concentric bullet.

What some are not seeming to understand is that yes, you can spin a bullet too fast and its negative effects range beyond "voids" and "metallurgical" makeup.

[Larry Gibson]

I agree that when you have two identical projectiles and one is slightly less concentric then yes that one will experience instability faster than the more concentric bullet.

What some are not seeming to understand is that yes, you can spin a bullet too fast and its negative affects range beyond "voids" and "metallurgical" makeup.

I concur.

Larry Gibson

[45 2.1]

I am glad to have all of you with math knowledge here!
2X2 gives me trouble. :mrgreen:

Would be nice if his answers were right though. Teacher gave F's to students with wrong answers.

[Junior1942]

I concur.

Larry GibsonSo do I.

[45 2.1]

I have been reading this thread with some skepticism regarding the RPM/balance theory, thinking it was more likely the boolit material yielding under the stress due to tremendous RPM's and the pressures required for the higher velocities.

I found the equation to calculate radial stress for a rotating cylinder:

radial stress = [(3+Poisson's ratio)/8] x density x (rotational speed in radians/sec)^2 x (radius)^2

The tangential stress calculation is a little different but since this is a solid cylinder the result is the same. I do not believe this is a combined stress situation but if anyone knows please correct me.

I did some calculations for a .30 cal. boolit since it is pretty commonly used.

I was surprised to find that even lead of only 6000 PSI ultimate strength which would be about 12 BHN will theoretically take 225,000 RPM.

The highest strength hardest lead/antimony alloy I can find (this is published data from a technical manual) is 8% antimony heat treated at 450 degrees F and quenched, resulting in 26.3 BHN after aging one day and has 12,350 PSI ultimate strength. It will take over 300,000 RPM.

Much higher RPM's for both than I had anticipated.

This is theoretical though and doesn't take into account misalignment or stress due to imbalance. Nor does it take into account frictional stresses in the bore or in the air, turbulence, imperfections, uneven obturation, etc. A slight wobble at those RPM's could be enough to cause increased stress and yielding.

Even so I guess I have to accept that it is enough above the 125,000 to 140,000 RPM threshold limit Larry uses to question whether yielding could be the culprit. This may also help explain how some shooters are achieving much higher velocities than normally accepted. If the boolits are well made and concentric and shot out of a good barrel they fit well, the RPM's shouldn't result in boolit yielding - not directly anyway.

So, I guess I haven't added much if anything to the discussion except now you can calculate the stresses in your boolits at whatever RPM you are developing.

I hope you guys do get together and shoot this one out - so to speak. I know I am still looking for an answer.

Longbow

Longbow-
You did a very good job at assesing the problems associated with cast at high velocity, much better in fact than anything posted so far. You are correct in your assumptions also. Perhaps, if the fellows busily slapping each other on the back and concurring amongst theirselves, would read the portion above in Blue, they would find out the true reason it works.

[78CJ]

I was simply adressing those who are assuming that one cannot have too fast of a twist, and the fact that destabilization can be achieved by too much twist. I think the variables have been adequately adressed concerning this particular scenario.

[78CJ]

If twist rate were mute, everything from a .223 to a .458 would be spinning 1:8's

[78CJ]

My point was that some just were not grasping that. Mostly due to lack of a little research, and partly due to the inability to understand.

[Larry Gibson]

45 2.1

"Even so I guess I have to accept that it is enough above the 125,000 to 140,000 RPM threshold limit Larry uses to question whether yielding could be the culprit. This may also help explain how some shooters are achieving much higher velocities than normally accepted. If the boolits are well made and concentric and shot out of a good barrel they fit well, the RPM's shouldn't result in boolit yielding - not directly anyway."

Slap yourself on the back, that is correct.

Larry Gibson

[runfiverun]

well......
according to this page of dialogue by being meticulous with our rifles and casting
and loading we can exceed the given rpm " threshold"
man, that is like finding out that magnum is more than maximum in a shotgun load
[ i always thought that maximum was well, maximum like you know the most]

[Larry Gibson]

well......
according to this page of dialogue by being meticulous with our rifles and casting
and loading we can exceed the given rpm " threshold"
man, that is like finding out that magnum is more than maximum in a shotgun load
[ i always thought that maximum was well, maximum like you know the most]

The magnum is still a magnum meaning you will still get better accuracy in or below the RPM threshold. How much worse accuracy gets above the threshold depends on you doing everything right and of course the moon and the stars are in line with Jupiter as Venus is the morning star..........and don't forget them nodes.......

Larry Gibson

Just making an attempt at humor guys.....but the RPM threshold remains the same.

[Bass Ackward]

How much worse accuracy gets above the threshold depends on you doing everything right and of course the moon and the stars are in line with Jupiter as Venus is the morning star..........and don't forget them nodes.......

Larry Gibson

Just making an attempt at humor guys.....but the RPM threshold remains the same.


Keep your day job, Johnny Carson's slot has been filled. :grin:

Let's see what the RPM focus gives us from a simplified view.

The only difference between a cast bullet and a jacketed bullet is that obturation of cast varies with the hardness. Copper obdurates at 35,000 to 45,000 for solid copper. That means an uncontrollable deformation that should be affected by RPMs just like cast. The rifling marks are the same. A copper bullet won't lead, but it sure loses copper. So balance changes there too.

If RPMS is a constant, then accuracy at 2000 fps would be better than 3000 fps. And accuracy at 3000, would beat any accuracy at 4000.

All jacketed bullets would perform based solely on balance and design. In other words, if a Hornady 150 SST didn't shoot for one guy, then it wouldn't shoot for anyone.

There would be no sense in working up a load or changing powders because velocity is velocity. Going up in powder charge would simply result in poorer accuracy. Because there is no such thing as an accuracy node for your barrel.

Bedding would have zero effect on accuracy.

Spinning a .308 caliber bullet that obturated to fill a .311 bore just would never shoot at all. And it would ALWAYS shoot better in a 12 twist barrel than a 10 twist. The most accurate barrels in the world would occur with slow twists and light bullets that could be stabilized with those twists only.

RPMs is a simplified view. More people can understand this jacketed logic to be false. All they have to learn is how to make cast like jacketed and RPMs becomes a footnote on this board.

[45 2.1]

Well the RPM of the 2750 fps bullet out of the 14" twist is 141,509; the top end of the RPM threshold. I actually always got the best accuracy out of those 3 cartridges in the 25-2600 fps range (128, 644 - 133,790 RPM). Out of the '06 with a 10" twist the RPM at 2750 fps would be 198,079; considerably higher than the RPM threshold which explains why you won't get 1 - 1.5 MOA with a 10" twist '06 using cast bullets at 2750 fps.

Your RPM answers are wrong. Grade schoolers can do better. Get it right if your going to post.


Just making an attempt at humor guys.....Humorous, NO, go ask for your day job back. but the RPM threshold remains the same. Only in your daydreams.

Increasing the RPM of a cast OR jacketed bullet increases this "detrimental" effect. Also with cast bullets there is that threshold where the RPM overcome the rotational stability and greater inaccuracy occurs. This is what I refer to as the RPM threshold.
Amazing it just happens with cast. To many generalizations on your part, get to the point and nail it down.

[Larry Gibson]

Keep your day job, Johnny Carson's slot has been filled. :grin:

Let's see what the RPM focus gives us from a simplified view.

The only difference between a cast bullet and a jacketed bullet is that obturation of cast varies with the hardness. Copper obdurates at 35,000 to 45,000 for solid copper. That means an uncontrollable deformation that should be affected by RPMs just like cast. The rifling marks are the same. A copper bullet won't lead, but it sure loses copper. So balance changes there too.

The copper bullet is a solid bullet within the bore and what obturation there is is minimal. A cast bullet, even when cast without voids is not solid within the bore as we have the lube groves and the bore riding nose. The cast bullet obturates much more at higher velocities (accleration) than does any jacketed bullet. Hence the imbalances are greater and RPM has a greater effect. Also RPM does adversly effect the inbalances of the obturates and rifling engraved copper bullet. It is just not to the degree that it does with cast bullets.

If RPMS is a constant, then accuracy at 2000 fps would be better than 3000 fps. And accuracy at 3000, would beat any accuracy at 4000.

Your thinking here is flawed; It is the rate of twist that is constant not RPM. RPM is dependant on velocity. Hence the RPM is much greater at 3000 fps than at 2000 fps. Accuracy with appropriate cast bullets will be at it's best in or below the RPM threshold regardless of velocity.

All jacketed bullets would perform based solely on balance and design. In other words, if a Hornady 150 SST didn't shoot for one guy, then it wouldn't shoot for anyone.

Not so; suggest you read most any reloading manual or treatise on the subject of what effects accuracy. A very good basic read is the chapter on Reloading and Bullet Accuracy in the Hornady Reloading manual.


There would be no sense in working up a load or changing powders because velocity is velocity. Going up in powder charge would simply result in poorer accuracy. Because there is no such thing as an accuracy node for your barrel.

So ok, you didn't like my attempt at humor...I won't quit my day job....ooops, I'm retired! I never said we shouldn't work up loads, never even hinted at it. I work up loads all the time. Not sure I understand your point here so I won't comment. Yes barrels have "nodes". Almost any quality barrel shoots more accurately free floated but some do require some bedding to shoot well. We have discused this before and pretty much agree. The "boss" and similar devices tune the nodes to the load. Working up loads tunes the load to the nodes. Given an accurate load for the nodes has nothing to do with how RPM adversely effects the flight of a cast bullet above the threshold.

Bedding would have zero effect on accuracy.

Your assumption, not mine.

Spinning a .308 caliber bullet that obturated to fill a .311 bore just would never shoot at all. And it would ALWAYS shoot better in a 12 twist barrel than a 10 twist. The most accurate barrels in the world would occur with slow twists and light bullets that could be stabilized with those twists only.

Most .308 bullets (are we talking cast or jacketed?) will in fact shoot. However, how well they shoot is a matter of question....but they won't shoot as well as a 311 bullet in a .311 bore. If speaking of cast bullets then it is probable they may shoot a little more accurately in the 12" twist. But you miss the point of the RPM threshold. The 10 and 12" twist barrels may very well be just as accurate in or below the RPM threshold. It is the 12" twist that will maintain better accuracy with a given bullet at a higher velocity. The reason is in the 12" twist barrel a bullet fired at 2,333 fps is at the top of the RPM threshold. In the 10" twist barrel the bullet is at the top of the RPM threshold at 1,944 fps. That is why a 12" twist barrel will shoot a cast bullet accurately at a higher velocity than will a 10" twist barre.

RPMs is a simplified view. More people can understand this jacketed logic to be false. All they have to learn is how to make cast like jacketed and RPMs becomes a footnote on this board.


No Bass, the RPM threshold is not a "simplified view". One still must do all the other things correctly to get accurate loads even in the RPM threshold. Yes, your jacketed bullet logic is indeed false. "Make cast like jacked"; that would be nice wouldn't it. However I don't think our intreped poster wanting to know why he can't get his 311291 to shoot any better than 5+" groups at 2400 fps out of his 10" twist '06 when his gets 2" groups at 1850 fps is going to learn to cast his 311291s like jacketed bullets. Do you?


BTW; have you worked up loads with your LBT bullet (using a more appropriate powder for this task than RL15 - I suggested 4895 with a dacron filler) in you 10" twist '06 from say 1600 fps up through 2100 fps as I asked sometime back? If so have you compared the accuracy to your top end HV loads in that rifle? I did this and to no surprise the LBT bullet was more accurate in and below the RPM threshold than it was in the 2400-2500+ fps range. Not to say accuracy was all that bad at HV but what I am saying is that accuracy was better in or below the RPM threshold. If you've done the test Please let us know the results. If not then I understand.


Larry Gibson

[Larry Gibson]

45 2.1

Getting kind of testy aren't you?

I do not believe my RPM figures are wrong. They are consistant with all the other posts I've made. There are several equations used to compute RPM. The one I use is; velocity/constant (each twist has a different constant) X 60 (since velocity is in fps this converts it to minutes) = RPM.

Example; 2750 fps divided by the constant of 1.166 (constant for a 14" twist) X 60 = 141,509 RPM

Perhaps you'd care to show me which equation you use and where I am wrong?

I do get to the point, you just fail to comprehend the point.

Be more specific about any "generalizations" I've made?

The point is; cast bullets will shoot more accurately in or below the RPM threshold than above it. That is pretty specific, do you understand?

Larry Gibson

[45 2.1]

I do not believe my RPM figures are wrong. Obviously They are consistant with all the other posts I've made. I'm sure they are. There are several equations used to compute RPM. The one I use is; velocity/constant (each twist has a different constant) X 60 (since velocity is in fps this converts it to minutes) = RPM.

Example; 2750 fps divided by the constant of 1.166 (constant for a 14" twist) X 60 = 141,509 RPM

Perhaps you'd care to show me which equation you use and where I am wrong? Easy, your so called constant is rounded giving wrong answers. Try this if you want a correct answer:
RPM = 720 x Velocity (in fps) divided by Twist (in inches). Try it and find out. The correct answer to two places is 141,428.57. You can round it now to 141,429.


The point is; cast bullets will shoot more accurately in or below the RPM threshold than above it. That is pretty specific, do you understand? Yours probably do that. If you balanced your loads out in each pressure range and your methodolgy was correct, it wouldn't make much of a difference, provided you could hold equally well. This is something you don't seem to understand or be able to do.

[Bass Ackward]

BTW; have you worked up loads with your LBT bullet (using a more appropriate powder for this task than RL15 - I suggested 4895 with a dacron filler) in you 10" twist '06 from say 1600 fps up through 2100 fps as I asked sometime back? If so have you compared the accuracy to your top end HV loads in that rifle? I did this and to no surprise the LBT bullet was more accurate in and below the RPM threshold than it was in the 2400-2500+ fps range. Not to say accuracy was all that bad at HV but what I am saying is that accuracy was better in or below the RPM threshold. If you've done the test Please let us know the results. If not then I understand.


Larry Gibson[/QUOTE]

Larry,

You always have an answer. :grin: But what makes you think cast bullets deform or get outta balance? You automatically ASSUME weakness, deformation and outta balance with cast.

WDWW of say 35 BHN is much more obturation resistant than a conventional jacketed bullet that is nothing more than pure lead with a thin copper skin. Conventional jacketed bullets can obturate down to 18,000 psi in handguns. Same with 30/30 bullets. They have to so they can expand. There is no deformation or out of balance with WDWW until you exceed the 45,000 psi level where obturation ONLY BEGINS.

Strangely enough, 45,000 psi is the level that a Barnes solid material bullets begins to obturate too. And some Barnes designs do have grooves. So except for grease for the protection of leading, which also supports the grooves and adds to bullet strength for cast, for all intents and purposes, WDWW cast has the same balance maintaining characteristics as a Barnes solid when shot at 45,000 psi. Neither bullet slumps or deforms except upon impact. So your out of balance / RPM argument against cast isn't valid when hardness is proper for the pressure, unless the bullet is molded poorly.

My 2800 fps load is a 45,000 psi estimate from Quickload. The predicted velocity is correct, so I can only guess that the pressure is too. That load is as accurate as I did with 4895 or RL7 in the zone with that bullet in this gun. And if you substitute a 150 Barnes Tripple X bullet, the only thing you will notice is better accuracy with the cast with this load.

[leftiye]

Bass,
Not to argue with your statements, but doesn't the out of balance due to deformation in the barrel approach give a better argument against the RPM limit theory than perfectly balanced cast bullets would? In other words, it is the boolit imperfections that cause anything resembling a threshold, and perfectly formed boolits with perfectly cooked up loads create the situation where no threshold exists (at least until pressures and velocity go even higher). Did I miss something?

[sundog]

Leftiye, you didn't miss a thang. Best boolit in the world will not shoot good from a crap bbl. Of course, if you have a good bbl, it deserves a good boolit. A barrel is a swaging device. Whatever exits the muzzle is what you got to work with and nothing more.

[Larry Gibson]

I do not believe my RPM figures are wrong. Obviously They are consistant with all the other posts I've made. I'm sure they are. There are several equations used to compute RPM. The one I use is; velocity/constant (each twist has a different constant) X 60 (since velocity is in fps this converts it to minutes) = RPM.

Example; 2750 fps divided by the constant of 1.166 (constant for a 14" twist) X 60 = 141,509 RPM

Perhaps you'd care to show me which equation you use and where I am wrong? Easy, your so called constant is rounded giving wrong answers. Try this if you want a correct answer:
RPM = 720 x Velocity (in fps) divided by Twist (in inches). Try it and find out. The correct answer to two places is 141,428.57. You can round it now to 141,429.


The point is; cast bullets will shoot more accurately in or below the RPM threshold than above it. That is pretty specific, do you understand? Yours probably do that. If you balanced your loads out in each pressure range and your methodolgy was correct, it wouldn't make much of a difference, provided you could hold equally well. This is something you don't seem to understand or be able to do.


You are kidding me aren't you? We use two different equations so what makes yours any more right than mine? We're talking a threshold of 15,000 RPM and a total of 141,429 or 141,509 and you tell me grade schoolers can do better. My calculation is correct by my equation so perhaps your textbook is out dated. But really, 80 RPM out of 141,000? For crying out loud a 50 fps shot to shot variation will have a higher RPM variation than that (around 2,500 RPM).

I understand how to load and how to shoot very well. Any time you want to shoot along side of me you are welcome to, I like a good shootin' match. You have been asked numerous time to explain AND show on this forum how well you shoot at high velocity. You have not shown anything. Your usual response is something about being better served by PM. That's hogwash. I'll ask again for you to show us how you consistantly shoot better groups above the RPM threshold than below it?

Larry Gibson

[Larry Gibson]

Bass

Come on now....."But what makes you think cast bullets deform or get outta balance?" It's called obturation and you speak of it quite often.

No I don't always have the answer, always willing to try and learn. Which reminds me; I'm still waiting for that test of your LBT bullet. Show me it doesn't shoot consistantly better in or below the RPM threshold than it does above the RPM threshold and I will learn. Until then you've proved nothing other than you can get pretty decent accuracy at high velocity with that bullet but then I did also.

Larry Gibson

[Larry Gibson]

Bass,
Not to argue with your statements, but doesn't the out of balance due to deformation in the barrel approach give a better argument against the RPM limit theory than perfectly balanced cast bullets would? In other words, it is the boolit imperfections that cause anything resembling a threshold, and perfectly formed boolits with perfectly cooked up loads create the situation where no threshold exists (at least until pressures and velocity go even higher). Did I miss something?

Pretty good train of thought but remember that the RPM effects the bullet (cast and jacketed) during flight, not while in the barrel. Perhaps Bass and 45 2.1 cast perfect bullets and shoot them out of perfect barrels with perfect loads ergo they are not defective (unbalanced) and then as you say the RPM will not adversely effect them. They have not shown me (us) that yet but I am waiting. After all I am the unlearned one who can not cast good bullets, can not load them correctly nor can I apparently shoot well. Oh yeah, I'm not very good at math either. Don't have to ask me as they say so. However the fact that us of the ignorant mass can't get cast bullets to shoot as well above the RPM threshold as we can shoot them below the RPM threshold says something about it's existance.

Larry Gibson

[runfiverun]

question here is there any way that a gain twist would affect what is or isn't
going on here ?
i know that you would still end up at 12 or 10 twist but....?
and #2
if you had an action that would support the x57 case long magazine
with 308 boolit.
what wold your bbl be like, and why?
really curious...

[Larry Gibson]

A gain twist might get you a little less obturation in the barrel, hard to say. I'd still want it to end up at a 14" twist. Preference right now is a Shilen stainless 26" heavy sporter match barrel with 14" twist and the chamber cut to 30x57 with a tight neck 30-06 reamer.

That weight barrel would be heavy enough to be accurate but still light enough for a walk through the woods hunting. The 14" twist is fast enough to stabilze medium to light/heavy cast bullets (150 through 200 gr) up through 2500+ fps. That is still within the RPM threshold and accuracy should be excellent. The case capacity is perfect for 100 % loading density with the slower powders like RL19/22, H4831SC and several others. This will give a slow time pressure curve lessoning the adverse effects of accelleratin on the bullet. The pressure at 2500 fps should still be below 45,000 psi also. The '06 length throat and 14" twist would optimise the accuracy/HV potential of Bass's 154 gr LBT bullet. Though if I were looking stricly at that bullet I would go with a 16" twist. I'vea M98 '06 that has been my favorite hunting rifle for years. The throat is getting pretty rough and she isn't as accurate as she used to be. I've been giving some though to rebarreling that M98 just as mentioned above.

Larry Gibson

[45 2.1]

You are kidding me aren't you? No, i'm not. We use two different equations so what makes yours any more right than mine? Same equation arranged differently. Don't believe me, ask Felix for confirmation and which gives the correct answer. We're talking a threshold of 15,000 RPM and a total of 141,429 or 141,509 and you tell me grade schoolers can do better. They do better than you did. My calculation is correct by my equation so perhaps your textbook is out dated. Its from the Algebraic Operating System, see if you can find that. But really, 80 RPM out of 141,000? For crying out loud a 50 fps shot to shot variation will have a higher RPM variation than that (around 2,500 RPM). Whine, whine, whine.

I understand how to load and how to shoot very well. Any time you want to shoot along side of me you are welcome to, I like a good shootin' match. You have been asked numerous time to explain AND show on this forum how well you shoot at high velocity. You have not shown anything. That is on the 6.5 thread, which is in progress. I know you've seen it. Your usual response is something about being better served by PM. What I would say to you should be by PM or face to face. Irregardless, i'm through trying to explain things to you. We disagree on many things and that will have to be that. That's hogwash. I'll ask again for you to show us how you consistantly shoot better groups above the RPM threshold than below it?

[charger 1]

I do this a lott simpler than you fellas. I stick things in my gun based on simple theories like throat bore fit, pressure bla bla bla. And baby it works. But ya know. When I was hot rodding the lott and getting one hole accuracy, there was a point at which I had to stop. Now the accuracy didnt get so bad that you couldnt hit and kill anything on planet earth, I'm talin it went from 1 hole to 1 moa and here is where it started to go
2580 FPS in a 14 twist barrel
So 720 x 2580 / 14 = aprox 133,000. I kept trying different things but thats still where my lovely worm holes STARTED to open.... Yep I'd say theres somethin to this upper limit stuff which I'm now getting proven to me strictly by accident....


OK back to the:takinWiz:

[Bass Ackward]

Show me it doesn't shoot consistantly better in or below the RPM threshold than it does above the RPM threshold and I will learn. Until then you've proved nothing other than you can get pretty decent accuracy at high velocity with that bullet but then I did also.

Larry Gibson


Larry,

I thought that with the answer above your question became rhetorical. And as 35 Remmy says, this just keeps going on. And not to be cruel, it only goes on because you won't buy an LBT mold and do it yourself. If you did, you would be on this side of the discussion.

To answer your question. The bullet will hold 3/4" with either 4895 or RL7. Since easiest accuracy occurs at this level, I suspect that you can get good groups with it or Red Dot or with any powder if you adjust the charge. That has never been my discussion. And the discussion has morphed.

I have equaled low velocity at HV. But not with Red Dot powder. Now I haven't tried every possible low velocity combination. But I haven't tried every high velocity combination either. But just like that country music song goes, "What part of equal don't you understand?" :grin: And that is without factoring recoil. I suspect that if the low velocity loads that did well kicked like the HV ones do, that I would have even beaten them in this case.

This is not a super bullet either. It's one design although a good one. Veral told me this one was "limited" because of the normal length GC groove and that his 160 grain would have a higher velocity potential. But if I take every brand of jacketed bullet and played with the best HV accuracy point, I would expect some would do better than others. IF you stay with factory designs, Loverins have a higher velocity potential than bore rides. There that ought to be known. But does that mean bore rides can't be shot at higher velocities than the zone? No. But it will be more difficult requiring you to take some corrective action.

IF your argument is based solely on the slowest twist required to stabilize, how many times have you heard me advocate 35 caliber for that reason? Weight without twist. Zero twist is a wall in the bore. Every longer measurement you make in twist rate from that point makes the rifling angle less. Which makes less of an impediment to forward motion in that bore. So in effect, you make your bullet stronger by not holding it back. You reduce the RATE of pressure. Destroy the bullet less, and you can push more RPMs with it. Common sense.

That's what your test is going to show. You will just draw the wrong conclusion from it at this point. Buy the mold Larry.

When this discussion all started, the conversation revolved around one single generality that morphed. That ALL lead designs would have a constant rate of deteriorating accuracy as RPMs went up simply because they were lead. No exceptions. There were side comments that they tore up. And there was this best accuracy line.

1. I have proven that lead hangs together. Heck it doesn't even deform if you match hardness. So if a person experiences that problem, they need to look for the "actual" cause and not blame RPM that magnifies it. Does that guarantee better accuracy for a 12 twist over a 10? No. Only an easier path to find it. The 10 twist may still turn out to be the more accurate barrel even if a couple a hundred pfs lower.

2. Failure of HV is a team effort between reloader and equipment mismatching, magnified by poor bullet design and improper hardness phenomena that their top end will be what it is and RPM WILL affect it. If they destroy the bullet, RPMs will do bad things to it. But if they don't! Bullets are destroyed in the bore, not in air until they reach the point they start to melt. Fail to understand that, and you never take the correct steps required to improve. The benchrest boys stopped in the 2200 -2400 fps zone because they ran ultra small case capacities. 45,000 psi pressures peaked their performance at that velocity level. If I had a larger capacity case and a longer barrel to burn slow powders where 45,000 psi would produce higher (consistent) velocities, I could go on up even higher. Velocity is not the limiter or RPMs from the velocity, but pressure and rate of pressure.

3. Best accuracy is nothing, just words. Only when it is used to stop someone who may have an interest in becoming jacketed free. And you can. RPMs is a reality, not a cause.

Bottom line: Larry, you really, really need an LBT mold. Buy one and you will be on this side of the fence the next discussion. From that experience, you will learn things (mostly bullet design) that will improve your low velocity work too. Best money you will ever spend. It will become a collectors item one day when the artist passes. You won't lose any money on the mold. But you will shoot a lot more. :grin: With all your 30s, man on man, just selling your other molds will cover it. And it will change your opinion on those molds. Even at low velocity.

[felix]

Want: Rpm = Revolutions/minute = Rev/min = (r)

Given: Seconds/minute = Sec/min = (60)
Feet/second = Ft/sec = (v)
Revolutions/inch = Rev/in = (1/t)
Inches/feet = In/ft = (12)

Solve Using Dimensional Analysis Technique:

Rev/min = Sec/min * Ft/sec * Rev/in * In/ft

Shown Another Way:

Rev Sec * Ft * Rev * In
--- = ------------------------
Min Min * Sec * In * Ft

Now, Insert Values:

(r) = (60) * (12) * (v) * (1/t)

R = 720 * V / T

Therefore, At 10 Twist:
R = 720 * V / 10
= 72 * V

Therefore, At 14 Twist:
R = 720 * V / 14
= 51.5 * V

[45 2.1]

Therefore, At 14 Twist:
R = 720 * V / 14
= 51.5 * V

720/14 = 51.428571428..... (and keeps going which means its an irrational number). Why not leave the equation as R = 720* V/14. That way the answer is correct instead of rounding before the answer. That has caused many problems in the past and will continue as long as people reduce equations improperly. It does not round to 51.5 either by AOS rules.

[felix]

Agree, 100 percent. Rounding is appropriate for what we are doing, however, because how accurate is the tach/chrono? If you can guarantee the accuracy of that device to a million decimal places, then rounding will not be appropriate. ... felix

[45 2.1]

Agree, 100 percent. Rounding is appropriate for what we are doing, however, because how accurate is the tach/chrono? If you can guarantee the accuracy of that device to a million decimal places, then rounding will not be appropriate. ... felix

How many sources of error should we put in any system. Too many will reduce the final answer to a approximation only. There are other uses for RPM numbers than what we use them for, ones involving military technology.

[Larry Gibson]

45 2.1

Your opinion is noted but not taken seriously. In the formula I use (though it may be "out dated" by your school book standards) The constant is derived for each twist. It is based on the fact that velocity is measured in fps therefore a 12" twist at 2000 fps produces 2000 RPS and multiplying that times 60 (for seconds in a minute) gives RPM.

The constant for another twist is derived from dividing that twist by 12. I.E. a 10" twist divided by 12. The constant in this case is .8333333333 etc. Perhaps an "irrational number" to you but rounded off (the common practice) to three places it is .833.

Dividing the actual fps by this constant provides the real number of revolutions the bullet will make in in one second (RPS) at 2,000 fps. Then multiplying that number of RPS times 60 gives us the actual RPM.

The equation I use may be slower and a bit more cumbersome but it gives the actual RPM.

Old school perhaps but more accurate.

Larry Gibson

[Larry Gibson]

Bass

I am giving buying that mould serious thought if you note my post on another recent thread. However you must recall I did experiment with that bullet in a very accurate '06. I used your bullets, your loading methods and then loads and my own. The fact is (as I have reiterated numerous times) that while accuracy was pretty good at 2500+ fps (I never got anything but improved cylinder groups above 2600 fps) it was better in and below the RPM threshold. That is just like every other cast bullet.

However, I am open to changing my mind. Can you show me 5 consecutive (a sample of consistancy since you say it "will hold") 3 shot groups that are 3/4" at HV? Ok make it 1".

Since I am probably going to rebarrel my favorite M98 (refer to other threat) I will no doubt get the mould. I do expect good accuracy with it at HV in a 14" twist barrel.

You are correct (as usual) that lovern designs are more accurate. In fact I am getting ready to test the 311466 in 10, 12 and 14" twist barrels (308 Win). I also test the pressure (Oehler M43) of the used in the 12" and 14" twist barrels.

I have a few of your LBT bullets left and will also test (M43) them with the best load if you are interested? I can do it in the 308 with both twists or the '06 with 10" twist?

"When this discussion all started, the conversation revolved around one single generality that morphed. That ALL lead designs would have a constant rate of deteriorating accuracy as RPMs went up simply because they were lead. No exceptions. There were side comments that they tore up. And there was this best accuracy line."

Actually I think this subject comes up about every tome someone posts as to why the can't get accuracy above a certan fps level with cast bullets. They want to know how to make their bullet shoot as well at HV as it does at lower velocities. You and a couple others tell them all sorts of things to try. I tell them they won't get there from here with their cast bullet because of the RPM threshold. Neither of us are wrong. With a lot of the things suggested they can slightly increse velocity with their cast bullet and maintain accuracy. However they are not going to get the same accuracy out of a 311291 at 2500 fps that they get at 1800 fps out of their 10" twist '06. The reason is RPM. If you disagree show me an '06 that does shoot 311291 cast bullets as well at 2500 fps.

The RPM threshold is there. I don't believe I ever said "That ALL lead designs would have a constant rate of deteriorating accuracy as RPMs went up simply because they were lead. No exceptions." What I have been consistantly saying is;

Within the RPM threshold there is a level of RPM that adversely effects the imbalances of the bullet (caused by casting, sizing, setback during acceleration and uneven obtuation) overcoming rotational stability and inaccuracy at higher velocity (ergo higher RPM) results. That RPM threshold with medium/slow powders is 125-140,000 RPM.

That is a far cry from a "constant rate of deteriorating accuracy as RPMs went up simply because they were lead" which is not what I have said and am saying. You misunderstand what I am saying.

I agree with you about that pressure and rate of pressure is a limiter. I thoroughly expect the M43 to show that. However your use of the bench rester limiting out on pressure is only half of the equation (if 45 2.1 doesn't correct me on that math - pun intended) as they also use 16 and 18" twist barrels to slow down the RPM. With there's and your larger case it is a matter of reaching pressure with the slowest accelleration while keeping the RPM within or below the RPM threshold. It is what the benchresters do, what I do and what you'll do to achieve accuracy at high velocity with cast bullets. Thus we disagree; you state that pressure is THE limiter and I state that both pressure and RPM are limiters to HV and both must be considered. To quote you; "RPMs is a reality, not a cause." Yes RPM is a reality but not a cause, RPM is a reason. Quite a difference there.

Always appreciate the reasonable discussions, though we disagree on a couple points, we have. I probably will get the LBT mould but doubt I'll sell all the other moulds as they are useful too.

Larry Gibson

[joeb33050]

Larry posted some RPMs for bullets at different twists and velocities. 45 2.1 nastily corrected him. I looked into the matter.
http://sports.groups.yahoo.com/group/CB-BOOK/
in FILES
in EXCEL SPREADSHEETS WORKBOOKS
in TWIST MV RPM CALIBER ROTATIONAL SPEED
there is a calculator for getting RPM for any twist/velocity combination

Larry says 2750/14>141509
Calculator says 141428.57

Larry says 2500/14>128644
Calculator says 128571.43

Larry says 2600/14>133790
Calculator says 133714.29

Larry says 2750/10>198079
Calculator says 198000

Larry is using some sort of estimating method to find RPM.
45 2.1 has leapt on the infinitesimal differences and made much ado about nothing. Again.
Where are the moderators, when does 45 2.1s nastiness and foolishness get stopped? What's the matter with 45 2.1? Doesn't he need some quiet time? Could it be the dreaded buildup?
joe b.

[charger 1]

Larry I got a .460 380 grain LBT LFN spare I'll make you a half price deal on

[runfiverun]

i have seen 45 put some ideas and drawings up here showing
some of what he has/is doing.
i've also seen where larry is having a problem [observation] getting hv
results and explaining his observations of why

i know 45 isn't going to hold your hand on a boolit project
but he give you suggestions and try to nudge you in the right direction
as to how he was able to get his results.

i would like to see a collaberation of efforts here i have seen larry's
offer of trying some new stuff as well as his thoughts on a good bbl
and case size although i am biased towards this case
and think that some awfully awesome stuff could be accomplished as
there are enough of us interested here to get enough support to actually
know

there is enough foundering around trying this trying that.
that a direction should be picked and sought after.

a velocity and accuracy standard set and obtained?

[felix]

About the best we can do, Bob, without going to variable length word machines, like the
older IBM 1620/1401 series. Compilers exist running on mainframes which will generate code to emulate these older computers in numerical precision, such that any length of a number can be defined up to the limitation of memory. These older machines used what is called "word marks". I have mucho experience using all of these computers, new and old. ... felix


CRAY/IBM VAX IEEE
length (bits) 128 64 64
sign bit (s) yes yes yes
exponent (bits) 15 8 11
exponent bias (b) 3FFF 7F 3FF (not important for this discussion)
fraction (bits) 96 55 52
decimal digits accuracy 29 17 16

[onceabull]

Perhaps 45 2.1's post :" Kelly-i've got a lot of fairly pertinent PMs and e-mails detailing the dirt they don't want known. I think they know I've got it,too. You think this past stuff has caused a ruckus,Ha." (verbatim from the arab's board,posted 01/05/07) has got this boards staff backed up..for now ? [smilie=1: Onceabull

[Larry Gibson]

Joe

I appreciate your assistance here even though we seem to disagree on another thread it is at least a pleasant disaggreement. However I am not "estimating RPM but calculating them based on actual revolutions of the bullet. Look at a previous post to 45 2.1 where I explain the equation I use. It is old school granted but it is more accurate than the "quick" equation now in use. You are obviously good at math so look at the equation I'm using and tell me if it is wrong. Thanks

Larry Gibson

[Larry Gibson]

Larry I got a .460 380 grain LBT LFN spare I'll make you a half price deal on


Me thinks I should be wary of "greeks bearing gifts".

Larry Gibson

[joeb33050]

Joe

I appreciate your assistance here even though we seem to disagree on another thread it is at least a pleasant disaggreement. However I am not "estimating RPM but calculating them based on actual revolutions of the bullet. Look at a previous post to 45 2.1 where I explain the equation I use. It is old school granted but it is more accurate than the "quick" equation now in use. You are obviously good at math so look at the equation I'm using and tell me if it is wrong. Thanks

Larry Gibson

Larry;
There are a number of ways to write the way to get to the answer, none I've seen here is "wrong", some are maybe "better" than others. Keep in mind that I often make arithmetic mistakes.
If I did it right, I'd use MV X (720/T) = RPM. But I wouldn't calculate RPM, I'd use and did use an EXCEL workbook.
RPM has 5 or 6 digits at reasonable real-world velocity and twist.
Considering the chronograph accuracy, the accuracy with which the twist is cut and the variation in velocity; I'd suggest that rounding the RPM number to the nearest thousand, or maybe hundred, RPM, is closer to truth than writing the number in 5 or 6 digits.
Thus 123,456 RPM is more properly thought of as 123 thousand, or perhaps 123.5 thousand RPM.
Think about this. 123,456 RPM, means that we're sure that that 6 is a 6. We're sure it's between 123,455.51 and 123,456.49. Or more places if you wish. We're sure to at least one part in 100,000. Now twist comes in inches, sometimes in one decimal like 12.4" per turn. If twist were "true" to 1 part in 100,000 a 10" twist would be 10.XXA, where A is absolutely known. Now I don't remember anyone saying that any barrel has twist correct to .001".
Use your method if you wish, the error won't be significant, if I did the arithmetic correctly. Better yet, use that EXCEL.
All if I did it correctly; I'm having brain troubles and operations.
joe b.

[w30wcf]

All,
Interesting thread! Here's something to throw into the "mix".

Regardless of the velocity, a bullet fired from the same twist barrel, wether it's traveling 1,000 f.p.s. or 3,000 f.p.s. turns the same number of revolutions on the way to the target.

For example: 12" twist barrel / 100 yards To target = 300 revolutions regardless of the velocity. Obviously the higher velocity bullet is going to get there faster.:Fire:

Sincerely,
w30wcf

[felix]

WOW! Interesting idea, there! Bringing that thought into the discussion will throw all of the calculations into a loop. ALL man-made engineering functions depend on time being a consistent constant rate which cannot even be measured even though it hasn't changed since the beginning of time. WHAT???? The most perfect description of convolution???? I wonder how an atheist can define time. Whatever, the BR shooters either hate time (changing conditions), or have learned to deal with it. There seems to be no in-between psycho thoughts on the line. The BR sport typically gives one an idea about the importance of their thoughts about time vs faith. A true dichotomy. .. felix

[sundog]

W30WCF, I already mentioned that in post #38, third paragraph. Twist is a constant (for a particular bbl). Over a given distance, the boolit can only turn that many times, no more no less, regardless of velocity.

[Larry Gibson]

Thanks Joe

An excellent perspective. Guess it is pretty hard to say exactly what the RPM is down to the actual turn regardless of which equation is used. I believe I will round off to the nearest 500 in the future. Makes much more sense that way given the shot to shot variation of loads anyways (regardless of the SD;-)

Larry Gibson

[HORNET]

Aw, Joe, you can't introduce an idea like significant digits and ruin the fun. Just check on the calculator and see that the number of places after the decimal point can just keep increasing for a long time. Of course, it gets like measuring with a yardstick and reporting results in microns....

[Larry Gibson]

Bass, 45 2.1, et all

How about a GB on that 154 gr LBT bullet? I'd do it but with my comings and goings this year I won't be able to. Anyone interested in it?

Larry Gibson

[onceabull]

Larry G. I will be interested if it's NEI doing the cutting...(That's assuming that Mr.Smith wouldn't be interested other than at his full rate.... Onceabull

[joeb33050]

All,
Interesting thread! Here's something to throw into the "mix".

Regardless of the velocity, a bullet fired from the same twist barrel, wether it's traveling 1,000 f.p.s. or 3,000 f.p.s. turns the same number of revolutions on the way to the target.

For example: 12" twist barrel / 100 yards To target = 300 revolutions regardless of the velocity. Obviously the higher velocity bullet is going to get there faster.:Fire:

Sincerely,
w30wcf

I believe that automobile wheels turn the same number of revolutions over any distance, without regard to the speed. Also locomotives and ox carts. Any wheeled vehicle. What does it mean? Is it God at work?
joe b.

[Black Jaque Janaviac]

All,
Interesting thread! Here's something to throw into the "mix".

Regardless of the velocity, a bullet fired from the same twist barrel, wether it's traveling 1,000 f.p.s. or 3,000 f.p.s. turns the same number of revolutions on the way to the target.

For example: 12" twist barrel / 100 yards To target = 300 revolutions regardless of the velocity. Obviously the higher velocity bullet is going to get there faster.

Sincerely,
w30wcf

Hmmm. So as a bullet's forward velocity slows down so does it's rotational spin? I thought forward velocity changed while rotational spin remained relatively constant. The forward motion of a bullet is thwarted by the density of the atmosphere, whereas there is much less atmospheric resistance to spinning.

I prefer to use RPS instead of RPM: we're talking bullets, not vinyl!

So if a bullet leaves a 12" twist bbl at 1,000 fps it is spinning 1,000 RPS. Over the course of 100 yards the bullet has slowed to 800 fps. So as the bullet crosses the 100 yard mark it is now only spinning 800 RPS? Thiswould have to be true in order for the number of turns per distance to be constant.

If RPS remained constant, the number of turns per distance would increase as the bullet traveled downrange.

If RPS actually slowed down proportionate to the forward deceleration there would be a distance at which the bullet began to tumble. This would give long distance shooters fits because in order to have sufficient spin at 500 yards they'd have to start out with "excessive spin".

[DLCTEX]

I think that the leading of the bore in the case that started this thread is evidence that the problem starts there and the resultant disassembly of the boolit is a result of damage in the bore. I suspect that stripping, caused by attempted over rotation, causes the leading and results in an unstabilized boolit. DALE

[runfiverun]

the boolit will also get some de-stabilization when it breaks the sound barrier
goig up and down, i think this is part of the problem with nose slumping
even while it is still in the bbl

[Slowpoke]

Larry G. I will be interested if it's NEI doing the cutting...(That's assuming that Mr.Smith wouldn't be interested other than at his full rate.... Onceabull

Seems to me NEI isn't doing to swift as of late, if Veral won't or can't do a group buy maybe this would be a good time to try OLD WEST .

good luck

[w30wcf]

sundog,
I had read through all of the posts but, somehow, I missed it on the first pass.....easy to do at my age (at least that's my excuse). I do like examples though.

joeb33050,
Yes, God is at work but on much more important issues.:-D

Black Jaque Janaviac,
Information I have read on bullet spin decay indicates that it decreases much slower than the velocity of the bullet. If that were not true, there would not be any long range target shooting.

w30wcf

[Black Jaque Janaviac]

w30wcf

Black Jaque Janaviac,
Information I have read on bullet spin decay indicates that it decreases much slower than the velocity of the bullet. If that were not true, there would not be any long range target shooting.

OK. That's what I was told. But that doesn't mesh with the bullet-only-turns-so-many-times per distance traveld idea. Just to simplify the equation let's hold spin decay as null.

If a rifle is pitched 1:12" the rifling extrapolated from muzzle to the 100 yard mark should make for 300 turns over the distance regardless of velocity, or so I understand your early post.

If a bullet starts out at 3000 fps @ muzzle the spin is 3000 RPS @ the muzzle. By the time the same bullet passes the 100 yard mark, the forward velocity has decayed to 2000 fps while the spin remains at 3000 RPS. If I average the speed at muzzle and at 100 yards to estimate the flight time I get an average velocity of 2500 fps and a flight time of 0.12 seconds.

3000fps+2000fps/2 = 2500fps
and
300ft/2500fps = 0.12 seconds

So if the bullet takes 0.12 seconds to cover 100 yards and it is spinning at 3000 RPS the # of spins it made on its way to the target is actually 360.

3000 Rev/sec * 0.12 sec = 360 Rev.

Is my math wrong? Or is there an error in my assumptions?

[leftiye]

BJ
You're right, boolits with poorer BCs will turn a few more times while reaching a given target because they slow down more rapidly. Also, the "Same number of turns to target regardless of speed" theory is wrong for the same reason - faster boolits slow down more.

[Larry Gibson]

RPM of a bullet is the rotational speed of the bullet. It is established by the twist of the barrel and the MUZZLE velocity. It has noting to do with how much the bullet slows down by 100 yards. It's rotational velocity is very near what it was as it left the barrel. It is pretty close to that at much longer range also. The rotational speed of the bullet does indeed decay very slowly.

Larry Gibson

[floodgate]

' "The rotational speed of the bullet does indeed decay very slowly." Larry Gibson'

Indeed: There are reports of high-angle (near 90*) antiaircraft shells coming back down base-first and still spinning as they sat in their impact craters.

floodgate

[Junior1942]

Hummmm. . . . I guess the slow rotational decay is due to Newton's Law--an object in motion tends to stay in motion.

[Scrounger]

And don't forget that gravity is messing with it too. The gravity rate is constant but as the projectile loses velocity, it has more time to work on it and to more effect.

[44man]

All of this makes my head spin. Too many questions nobody can answer.
What is the optimum spin to keep any individual boolit stable at all ranges?
What happens when a boolit is underspun and transitions back through the sound barrier?
Does an underspun boolit start to wobble when it gets way down range like the top?
What is the relationship between foreward velocity and spin effect as the boolit slows?
Exactly how much does spin slow over distance? There is no doubt at all that it WILL slow unless in a vacuum. Air resistance is a tough customer.
If started out with a slow spin and it loses just a little spin over distance, at what point does the boolit go unstable?
Does an underspun boolit lose spin faster then a boolit with the proper spin? (Because of instability, speed of sound transition or wobble?)
All of the math and arguing only shows how much spin a boolit has when it leaves the muzzle but not what the boolit needed to stay stable.
So put the math to work and tell me exactly what every weight boolit for the .44 magnum needs as far as spin and rate of twist to stay stable and accurate to 500 meters. The velocity for the equations can be the book max velocities. The math work needs to be proven with actual field results.
I will stick by my guns and say if you underspin a boolit in a cartridge that will NOT support an increase in velocity, all is lost.
If you have a faster twist, the velocity can be slowly reduced to find the stability. To shoot VERY long range it is best to overspin a boolit and put up with less accuracy at short range before the boolit/bullet goes to sleep.
To apply what a BR shooter needs for an underspun bullet at 100 yd's to keep out yaw will not apply at 300 to 500 yd's. They want the bullet to be asleep soon after the muzzle. If you spin the top real hard, it will walk around until the spin reaches the perfect rate, then when it slows, it will start to wobble all over the place. The fast spin has yaw until it goes to sleep. But not enough spin creates wobble. Bullets do the same thing.
So all of the math has not answered a single question! [smilie=1: I don't care if a boolit spins 350 or 450 times to the target, I want to know WHAT the boolit ACTUALLY needs.
Tell me how to get a Marlin 1 in 38" twist to shoot better then my revolvers at 100 yd's! (No, I don't want to shoot 150 gr boolits!) The piece of crap needs Gyro-Jet bullets or fin stabilized bullets! My stinking arrows are more stable. :Fire:

[Larry Gibson]

Hummmm. . . . I guess the slow rotational decay is due to Newton's Law--an object in motion tends to stay in motion.

That would be the phenomenon.

Larry Gibson

[Larry Gibson]

I was running some military, factory and handloads through two .308s and two 30-06s yesterday over the M43 yesterday. I had the down range (100 yards) screens set up so along with the chamber pressures I was measuring muzzle velocity, down range velocity, time of flight and the BC. The test of some M118 Special ball through the two .308s was interesting and related to this topic.

The two rifles were my M70 target with 12" twist 26" barrel and my M98 Palma rifle with 14" twist 27.6" barrel. The test consisted of 10 shot strings through each rifle. I will list the actual numbers with the M70 first then the M98, e.g.; (M70/M98). The average velocities were within 14 fps of each other (2644/2630); note the difference of 14 fps. The ES and SDs (12,42/25,84) equal to what is normally got with this lot of M118. The down range velocity ES and SD was still consistant (11,40 - actually less ES and SD down range) with the M70 but the SD and ES had dramatically increased (27,91) with the M98s down range velocity loss which was greater than the M70s 173,199). The BC for the M70 was .517 but the BC for the M98 was .448. The average peak psi(M43) was 49,600 for the M70 and 48,200 for the M98. Group size for each 10 shot string was 1.1" for the M70 and 1.2" for the M98.

So what does this tell us? If judging by the 100 yard groups I'd have to say both were equally as accurate. Note; I have shot better groups with this M118 out of the M98 vs the M70 on other days. Obviously the 174 gr M118 bullets were having stability issues with the 14" twist in the M98 vs the 12" twist of the M70. This is evidenced by the bullets higher velocity loss, greater ES/SD down range than at muzzle and much lower BC when fired in the 14" twist M98 vs the 12" twist M70.

Obviously this explains the noticeable accuracy difference at 300 yards between the two rifles with this ammunition (1.5 MOA for the M70 and 2.75 MOA for the M98). Thus if just judging "accuracy" from 100 yards groups we would have been wrong to assume both as accurate as each other. Moral to the story is; testing at the longest range we intend to shoot will tell us what the accuracy accually is. Testing at close range can easily lead us to false assumptions.

Larry Gibson

BTW; I've a new barrel coming with a 10" twist so when I get it assembeld onto an action I will begin the tests of cast bullets in 10, 12 and 14" twist barrels in .308 Winchester. All tests will include group size at 100 yards, chamber pressure, muzzle velocity, down range velocity, BC and computed RPM.

[Ricochet]

Does anyone have Dr. Mann's The Bullet's Flight? All of 44man's questions sound like the kinds of things he would've investigated.

[Black Jaque Janaviac]

I've seen wind drift tables, trajectory tables, KE tables, even programs that will calculate all this stuff out for you - all for free.

But what 44man is asking for, "exactly what every weight boolit for the .44 magnum needs as far as spin and rate of twist to stay stable and accurate to 500 meters" just doesn't exist.

Perhaps such a compilation could be made, but I'm not willing to do it for nothing.

[44man]

Very true and answers to most of my questions do not exist. That is the point! To dwell on how fast a boolit is spinning doesn't answer what each boolit needs as far as twist and velocity. We all know that the longer a boolit gets, the faster the twist has to be. There is no magic twist that will shoot all boolits.
That is why the .244 Rem got shot down by the .243. The .243 shot heavy bullets better and the .244 was made for light varmint bullets. The .244 is a better round but the twist was wrong for deer bullets. The 22-250 is harder to get long range accuracy then the .220 Swift because light bullets have to be used.
It is also why my 45-70 BFR with the 1 in 14" twist outshoots every rifle I ever shot in that caliber.
To just tell me what RPM's my boolits are going will not tell me if it is right or wrong.
Just about every factory uses too slow of a twist for a lot of calibers but on others they get it right.
For revolvers, the BFR's have the most perfect twist rates I have ever seen. Each is a perfect match for the caliber. They did not depend on some pencil pusher to determine what the guns need.
I have a list published long ago telling the best twist rates for a lot of calibers and almost all are wrong, some so far out you need a round ball.

[Larry Gibson]

44man

I'm not sure what you mean by; "To just tell me what RPM's my boolits are going will not tell me if it is right or wrong" but the RPM threshold is not about stability of the bullet. The RPM threshold is about where the RPM adversely effects the rotational stability of a cast bullet causing decreased accuracy. It is assumed that the twist is sufficient to stablize the bullet normally.

Larry Gibson

[44man]

I understand and did get off track a lot.
What I was thinking about was that if the maximum rate of spin is reached for a cast boolit and it starts to come apart, hasn't the accuracy point for that boolit been long exceeded?
I feel each boolit design when matched to the twist has a very short span for a sweet spot and to shoot under or over that gives the same result of poor accuracy at different ranges.
An under spun boolit is usually pretty accurate at close range.
Are we really sure we reach the stability limit of lead when a boolit is spun too fast? Or was yaw introduced so the boolit rotates around the flight path until it goes to sleep? That boolit might shoot tighter groups at 300 yd's then it does at 100.
I have done it, seen it happen and even watched boolits/bullets in a spotting scope.
Can we really say the spin rate is too fast when only one distance is shot?
Anyway, that was my point, no argument intended, just trying to get things clear in my feeble mind and understand the math. :confused:
I don't feel I want to push things to the point of having a lead cloud out in front of a gun! :mrgreen:
Which brings me to a question sticking with me; What would the velocity limit be with a cast boolit from my 6.5 Swede that has a 1 in 8" twist? Reading everything here has me wondering, I don't have a mold yet and never tried it. Should I be scared off by the twist rate?
So you see, I have ulterior motives! :drinks:

[Larry Gibson]

44man

"What I was thinking about was that if the maximum rate of spin is reached for a cast boolit and it starts to come apart, hasn't the accuracy point for that boolit been long exceeded?"

It does appear the accuracy is long gone. However I've got to say I have not had a cast bullet "come apart" in flight due to RPM, but then I've not tried to push them that fast. I know that a Hornady SX bullet with its soft lead core and thin jacket will spin apart somewhere above 180,000 RPM. So will some other jacketed varmint type bullets. Since cast bullet alloys are somewhat harder than lead they may not spin apart as easily. Again I don't know because I've not tried. Fact is accuracy is long gone before we'll spin one apart using our normal cast bullet alloys.


"I feel each boolit design when matched to the twist has a very short span for a sweet spot and to shoot under or over that gives the same result of poor accuracy at different ranges."

I think you may be correct for the most part but there are exceptions or at least cases where the sweet spot actually has a large span.

"An under spun boolit is usually pretty accurate at close range."

Exactly the point I was trying to get across with the test. The accuracy at 100 yards was comparable but the BC of the bullet (same box of M118) fired in the 14" twist was noticeably lower than the bullets fired in the 12" twist. This is a very good indication of stability problems with the bullet. There is a noticeable accuracy difference at 300 yards as pointed out.

"Are we really sure we reach the stability limit of lead when a boolit is spun too fast? Or was yaw introduced so the boolit rotates around the flight path until it goes to sleep? That boolit might shoot tighter groups at 300 yd's then it does at 100. I have done it, seen it happen and even watched boolits/bullets in a spotting scope."

I to have seen that but not with enough frequency to bet on it. Most often a bullet that is inaccurate at short range because of stability problems will be even more inaccurate at longer ranges.


"Can we really say the spin rate is too fast when only one distance is shot?"

No we can't.

"Anyway, that was my point, no argument intended, just trying to get things clear in my feeble mind and understand the math. :confused:"

Point well taken.

"I don't feel I want to push things to the point of having a lead cloud out in front of a gun! :mrgreen:"

Me neither, I always noticed that when an SX, Blitz or other varmint bullet blew up out in front of the rifle the target walked away unscathed! Not exactly what I had in mind....

"Which brings me to a question sticking with me; What would the velocity limit be with a cast boolit from my 6.5 Swede that has a 1 in 8" twist? Reading everything here has me wondering, I don't have a mold yet and never tried it. Should I be scared off by the twist rate?"

I don't let the twist of the Swede 6.5 scare me off. You just need to understand what it is doing RPM wise is all. I have played with several Swedes and several different cast bullets. I'm of the opinion that the Lyman (Lovern) 266455 is the best regular cast bullet design for the military chamber/throats. Accuracy with most cast bullets will be best in the 1400-1500 fp. With a bullet that fits the throat as well as 266455 does and with some tweeking you can boost this up into the 1700 fps range. Again the swede makes for a pretty decent cast bullet shooter if you understand the effect RPM wil have on the bullet. 45 2.1 and others claim higher velocity with accuracy but most of us haven't seen it, even when using their loading techniques. Who knows, maybe you succede where most of us haven't.

"So you see, I have ulterior motives! :drinks:"

It has been said here that trying cast bullets in the Swede can make a man drink! I drink anyways so it doesn't matter to me. Cheers!

Larry Gibson

[44man]

Thanks Larry, I have to look at that boolit. I have been putting it off because my barrel is pitted some but shoots great with jacketed. I don't shoot it as much as I would like because of the price of bullets.
And I can fall back on the bottle too! :drinks:

[Black Jaque Janaviac]

It has been said here that trying cast bullets in the Swede can make a man drink!

Well then . . . all the more reason to give it a try!!!:drinks:

Part of the problem with trying to speak with any wisdom regarding the affects of spin on a cast bullet is that I know of no one who has done testing that controls for the effects of internal ballistics.

So often "too much twist" means stripping the rifling, and it really has nothing to do with the external ballistics of the bullet in flight.

One of my favorite guns is an Early Virginia flintlock with a 42" barrel. The long barrel really doesn't seem to set me back at all when in the deer woods. So I've often wondered what could be done if a guy played with a long 40+ inch barrel and slower smokeless powders. Could you get better cast bullet velocities if you accelerated the bullet over 40 inches instead of 22 inches?

[44man]

That sounds a lot more sane then shooting 150 gr's of powder from a 24" barrel with an inline! [smilie=1:

[leftiye]

B.J. It would fer sure lower exit pressures at the muzzle. Might make high velicities with lower pressures too. Problem is that slower powders don't burn well at low pressures. Maybe we should outlaw using the expression RPM on this board? Label it a swear word.

[Black Jaque Janaviac]

RPM is better suited to vinyl discs and ... maybe ... the .45-70. But the bullets I shoot are best measured in RPS!:twisted: