Twist confusion

[Lead melter]

OK, just so I keep my facts straight, someone with a lot more knowledge than me jump in here with an answer.

As I understand it, in the world of jacketed bullets, a heavier bullet is longer [in a given caliber, of course] and often benefits from a faster rate of twist for proper stabilization. This also holds true for a homogenous bullet material, since the given weight of this type bullet will require it to be longer as the material is less dense than lead.

As examples, the 220 grain .308 Hornady lead core bullet is longer than the 180 grain Hornady lead core bullet. Since the bullet cannot increase its circumference, it must therefore be longer, and MAY benefit from a faster twist rate barrel to impart better stabilization and thus the possibility of better accuracy.
The 180 grain Barnes solid copper bullet is longer than the 180 grain Hornady lead core bullet since the Barnes bullet material is less dense than the Hornady lead core/gilding metal construction. It would stand to reason that the Barnes bullet might also benefit from a faster twist rate for the same reason listed above.

Am I right so far?

If so, then here is my confusion:

When reading a few posts about twist rates with Pb boolits, it seems to me [and maybe I'm getting this wrong] that a heavier for caliber boolit often requires a SLOWER twist for optimum performance. If what I seem to gather is correct, does it have to do with boolit velocity/twist rate/RPM spin to the point where a faster twist barrel will strip the boolit as it is pushed down the barrel? Or have I missed the whole idea of what is going on here?
Is there some sort of equation or formula to determine the "sweet spot" for a boolit caliber/weight/design?

Please have patience with me on this subject. It's all new to me and I'm having a hard time getting my mind wrapped around this idea.[smilie=b:

[NSP64]

I feel your pain:killingpc I don't get it either.

[WickedGoodOutdoors]

http://physics.bu.edu/~duffy/py105/Torque.html



This is a simple expanation why.

[NSP64]

So it has to do with the weight of the door pulling the block off the table!

[mooman76]

OK, I had to read your post a couple times and I think what you are getting at. yes a longer bullet is heavier but like every rule there are always exception. A blunt nosed bullet of the same weight as a pointed bullet is going to be shorter so if you want to go with a heavier bullet and you are getting to end of stablisation in your twist a round or flat nose bullet might work where a spear point won't. But what you stated is basically true.
Now a bigger bullet not a heavier bullet will benefit from a slower twist for example a 50 cal M/L with stablize a maxi ball (bullet) with a 1/48 twist where a 32 cal with a 1/48 will not. Then there is the fact that if you try to push it too fast it jumps or strips the rifling and will not stablize because it didn't follow the twist. This is more likely to happen with cast bullets because of the lead be softer of coarse.
There is a formula out there actually more than one but the one I remember is called the Green hill formula. It is not absolute but getts you real close. If you do a search you will find it.

[Lead melter]

http://physics.bu.edu/~duffy/py105/Torque.html



This is a simple expanation why.

Not simple 'nough for me.:killingpc

So maybe I need to restate the question in a simpler form; does a heavier for caliber cast boolit require a slower rate of twist. If so please elaborate in laymans terms.

I just did a quick check of the Ranch Dog TLC359-190-RF boolit specs and punched that data into my Lee Shooter program to find what the minimum twist would be. There is no provision for the weight, design, or velocity of the boolit...just diameter and length.[.359 and .766]. It throws out a minimum twist of 1:25.8". If I'm not wrong, almost all 35 caliber rifles still carry a twist rate much faster than that. Still confused.

[Blammer]

OK, just so I keep my facts straight, someone with a lot more knowledge than me jump in here with an answer.

As I understand it, in the world of jacketed bullets, a heavier bullet is longer [in a given caliber, of course] and often benefits from a faster rate of twist for proper stabilization. This also holds true for a homogenous bullet material, since the given weight of this type bullet will require it to be longer as the material is less dense than lead.

As examples, the 220 grain .308 Hornady lead core bullet is longer than the 180 grain Hornady lead core bullet. Since the bullet cannot increase its circumference, it must therefore be longer, and MAY benefit from a faster twist rate barrel to impart better stabilization and thus the possibility of better accuracy.
The 180 grain Barnes solid copper bullet is longer than the 180 grain Hornady lead core bullet since the Barnes bullet material is less dense than the Hornady lead core/gilding metal construction. It would stand to reason that the Barnes bullet might also benefit from a faster twist rate for the same reason listed above.

Am I right so far?

.[smilie=b:

Yes that is correct


If so, then here is my confusion:

When reading a few posts about twist rates with Pb boolits, it seems to me [and maybe I'm getting this wrong] that a heavier for caliber boolit often requires a SLOWER twist for optimum performance. If what I seem to gather is correct, does it have to do with boolit velocity/twist rate/RPM spin to the point where a faster twist barrel will strip the boolit as it is pushed down the barrel? Or have I missed the whole idea of what is going on here?
Is there some sort of equation or formula to determine the "sweet spot" for a boolit caliber/weight/design?

Please have patience with me on this subject. It's all new to me and I'm having a hard time getting my mind wrapped around this idea
.[smilie=b:

From what I have experienced and understand, when shooting lead boolits you'll want a twist that will generally be a little slower for the heavy cast boolits. This slower twist will allow you to shoot them at a higher velocity.

in your 30 cal example above: I have a 226gr lead cast 30 cal boolit that I shoot in my 30-06. It shoots fine, but at not a very high velocity. From what i understand, if I either have a slower twist barrel, OR cast my boolits harder, I can shoot them faster.

so yes, when I started casting boolits too, I was confused when others stated that i needed a slower twist for a heavier boolit. That seemed contrary to my previous experience with jacketed bullets, needing a faster twist for the heavy wts to fly well.

[AZ-Stew]

Melter,

The longer the boolit, the faster the required twist to stabilize it as it flies unguided through the air. This assumes the same launch velocity. I believe the actual requirement is RPM rate for a given length. Some folks have noted that they can stabilize a long bullet by driving it faster in a barrel that has a theoretically slow twist rate for that length boolit.

Now, in the world of cast, we have some additional issues to deal with. Lead alloy isn't as strong as copper. This gives us two things to deal with:

1.) RPM rate. The faster the boolit rotates, the more centripital force is applied to the outer diameter of the boolit. If this force exceeds the strength of the alloy, the boolit will throw itself to pieces radially as it flies.

2.) Ability of the boolit to survive the initial rotational acceleration caused by the rifling. In other words, will it rotate when it hits the lands, or will the lands of the rifling strip off the outer portion of the boolit and the remainder of it just squirt out the barrel? This can be avoided with harder boolits or slower muzzle velocities.

I don't think I've ever encountered either condition. Maybe I'm not shooting fast enough. I do have a 190gr Lee .30 cal mould (discontinued) that has shot OK out of several 1-10 twist rifles, but not ever spectacularly good. I believe there are a number of reasons. I believe this boolit bends when sized, but don't have a tool to measure it. I also believe the nose compresses lenghtwise and expands radially when sized, making it difficult to chamber the boolit once it's loaded into a cartridge because the long land-riding bearing surface is larger in diameter at the nose than it is near the front driving band. None of this contributes to accuracy, but to get back on point, I don't believe the twist rate has near as much to do with the inaccuracy I've experienced as all the other factors listed above. This is an example of a long boolit that shoots as well as can be expected (all things considered) in a number of normal-for-caliber twist rate barrels.

All in all, the boolit must be stabilized if any accuracy is to be achieved. In addition, the velocity must be kept below that which would destroy the boolit via excess rotational speed or stripping in the lands. I don't have a formula for this, but I'm guessing someone here will.

Regards,

Stew

[44man]

One reason it is so hard to figure are the extreme differences between all of the cast boolits.
Jacketed bullets are pretty much fixed in form with only small differences.
With cast we have all kinds of nose shapes and lengths, drive lengths and alloys.
To take just the length and diameter and predict a twist is like barking at the moon. That's what Marlin did with the stupid twist in the .44.
In general out of a rifle, cast is shot slower so a long drive length boolit does benefit from a faster twist.
When shooting heavy boolits from a revolver, I am a firm believer in a faster twist. It is about 1000 times easier to find the accuracy point with a faster twist revolver without running out of the velocity limit.

[missionary5155]

Good morning
Another factor is that many companies use a FASTER twist than really is necessary for the average boolit most people shoot.
My CZ 500 30.06 now 30 years old shoots 220-130 grain J thangs Fantasticly. It has a 1-10 twist which would probably stabalise a 230 and maybe a 240 grain RN. So who shoots heavy projectiles like that anymore (Me) and a few others. But most people stick to 150-180 because they do not hunt BIG Bitting critters. That is what the local hardware sells.. The Gun rags tell-em it is all they need. Just buy the latest Suder-Duper Thumper and you never will track a wounded critter again.
But the factories turn out barrels that will shoot most anything because they do NOT want bad publicity because their barrel will not shoot a 220-240 grain .30 cal J thang. They cover the bases and play the odds. And that makes sense for profits.
In a Perfect world we could order a 1-14 twist 30-06 and happily shoot Boolits downrange at a more productive FPS without the need to tweak and fiddle about so much. WE are the minority in the world of barrel supply and demand. If all 7000( possible 500 ? would be enough) of us called Remington or whoever and said "We want a 1-12 or 1-14 twist barrel on a 30-06 ... here´s $100 down from each of us"... guess what would be in the mill next month. We are the minority and MONEY / PROFITS guide the decisions.
There´s an Idea for a Group buy... ONCE A YEAR.. Cast Boolit Rifle...
God Bless you all.

[klcarroll]

I'm sure that the issue of "stripping" a lead bullet is one of the considerations that encourage the use of slower twists.

Another point is the simple fact that a homogenous lead boolit is always going to be shorter than a jacketed round of the same caliber and profile (lead being much denser than the jacketing material); ……And consequently it will not require as fast a twist.


Kent

[Larry Gibson]

The RPM for stabilizarion in a given caliber is dependant on the length of the bullet. A cast bullet of 220 gr sans jacket in a .30 caliber is shorter than a jacketed 220 gr bullet. Therefore it requires less tiwst to stabilize it at a given velocity. Has to do with the density of the bullet per it's length. Since a lead alloy bullet is denser than it's lead/copper jacketedcounterpart (given the same bullet profile) it is the shorter bullet.This is why cast bullets up through 200 gr stabilize in a 14" twist. A 10" twist '06 barrel will stabilize up through 250 gr RN cast bullets without problems.

Larry Gibson.

[Bret4207]

All this talk of twist has my head spinning!:groner:


Isn't nice to have someplace to go where guys will take the time to explain stuff like this. Interesting question and good answers. I learned a lot.

[bobk]

Larry,
Is that actually true, that a jacketed 220 is longer than a cast 220? The jacketed bullet has a lower density, but the lube grooves reduce the weight of the cast bullet, necessitating that it be longer to achieve the weight. Certainly a straight-sided PP bullet would be shorter, but the grooved bullet would be longer than that. Unless we are talking about a FMJ 220, with a very thick jacket, I suspect that the actual length measurements of the ordinary 220 jacketed and the grooved cast are not very different. I have none of either. Closest I could come to in approximate weight and form would be to compare a 466 with a 150 sp.
Bob K

[bobk]

Lead melter,
As I understand it, you get the best accuracy with enough twist that the bullet is just stabilized. Now with jacketed, going faster than this twist rate does little or no harm, because the bullets are pretty homogeneous, and the jackets are very concentric. With cast, however, there seems to be a sweet spot where the bullet is being spun fast enough to stabilize, but not so fast as to magnify the imbalances created by internal, therefore unseen, imperfections in the bullets.

I think if you were to go to the trouble of weighing your bullets, and discarding the lighter ones, as opposed to segregating them by weight range, you might see some improvement. The light bullets likely have internal voids or poorly filled out edges to the grooves, and while some of them might match the weight of other "light" bullets, the imperfections would hardly be uniform.

Bob K

[KAF]

1.) RPM rate. The faster the boolit rotates, the more centripital force is applied to the outer diameter of the boolit. If this force exceeds the strength of the alloy, the boolit will throw itself to pieces radially as it flies.

1cen·trif·u·gal Listen to the pronunciation of 1centrifugal
Pronunciation:
\sen-ˈtri-fyə-gəl, -ˈtri-fi-, especially British ˌsen-tri-ˈfyü-gəl\
Function:
adjective
Etymology:
New Latin centrifugus, from centr- + Latin fugere to flee — more at fugitive
Date:
circa 1721

1 : proceeding or acting in a direction away from a center or axis 2 : using or acting by centrifugal force <a centrifugal pump>



cen·trip·e·tal Listen to the pronunciation of centripetal
Pronunciation:
\sen-ˈtri-pə-təl\
Function:
adjective
Etymology:
New Latin centripetus, from centr- + Latin petere to go to, seek — more at feather
Date:
1709

1 : proceeding or acting in a direction toward a center or axis

[atr]

Lead Melter....
think of the bullet as a gyroscope because rotational stability is what its all about.

Remember the gyroscope we all had as a kids.....when the rotational rate of spin was high the gyroscope was stable, as the rotational rate got slower and slower the gyroscope started to tilt until finally it fell over....
For boolits the rate of twist is what is important, not the straight line velocity....the straight line velocity is not important to bullet rotational stability

for example.....a 1:12 rate of twist will rotate the bullet 1 revolution for every 12" of barrel length. No matter how fast (velocity) the bullet is traveling down the barrel it will never rotate any faster than the rate of twist !!!
As you increase the rate of twist, say 1:8 you are increasing the rate of rotation and imparting more rotational stability....

We simplify by saying that a faster rate of twist (1:8) will stabalize a bullet better than a slower rate of twist (1:12)

You can complicate matters be introducing such things as bullet shape (pointed vs blunt) and changes to the center of mass of the a bullet ....etc, etc.

BUT to keep it simple just remember the gyroscope and rotational stability.
I hope this helps

[montana_charlie]

This is a simple expanation why.
http://physics.bu.edu/~duffy/py105/Torque.htmlNot simple 'nough for me.
You want simple?

You men know how a really full bladder will make you wake up with a certain painfully intense 'stiffness' in the package?

So, you walk into the bathroom to relieve the pressure.
You try to crank that member down to point at the porcelain bowl.

If your feet come off the floor...that's 'torque'!
CM

[joeb33050]

Not simple 'nough for me.:killingpc

So maybe I need to restate the question in a simpler form; does a heavier for caliber cast boolit require a slower rate of twist. If so please elaborate in laymans terms.


No. That's NO. Heavier = longer bullets in a given caliber require a FASTER twist to stabilize. NOTE that the twist given by any formula is the MINIMUM twist required to stabilize a bullet.
A 110 grain bullet might stabilize at 16" twist, a 220 grain bullet might require a 10" twist. 10" is FASTER than 16".

Denser bullets require slower minimum twist (Copper jacketed vs. lead vs. depleted uranium)
Faster bullets require a slower minimum twist, the effect of velocity is SMALL
Denser media through which the bullet travels requires faster minimum twist. Bullets that stabilize at 10,000 ft. may not stabilize at sea level and won't stabilize in water.
Some contend that the slowest twist that will stabilize a given bullet/load will yield best accuracy.
joe b.

[jsizemore]

Think of it this way. A short wide top can turn slower and be stable, while a tall skinny top has to spin faster to be stable. When the mass of the skinny top is moved closer to the tip, it will become unstable quicker than the mass being at the base. I hope that is clear. Now if you have your top spinning very fast, an outside force acting from the side will have more effect than a slower spinning top. A benchrest shooter won't use a fast twist barrel because the wind will have more effect than a slower twist. Hope that helps.

[S.R.Custom]

...For boolits the rate of twist is what is important, not the straight line velocity....the straight line velocity is not important to bullet rotational stability...

Not entirely true. Do a Google search on the "greenhill formula" for determining optimal twist rates....

http://www.mountainmolds.com/helpGreenhill.htm

Some sources will raise the constant in that formula from 150 to 180 to take into account the increased RPM of bullets fired faster than 2800 fps...

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

(scroll down to the section on "Twist Rate")

[Wayne Smith]

One small correction for all of us to remember when comparing cast to condom bullets. It is not the length of the bullet that matters it is the BEARING LENGTH of the bullet. Condom bullets tend to have a lot of the bullet length that does not bear on the rifling. As much as one third of the length may not bear.

This is rare in lead boolits. We usually have most if not all of the length of the boolet bearing on the rifling. Thus when using something like the Greenhill formula you must use the Bearing Length of the Boolit/bullet as your variable.

[montana_charlie]

It is not the length of the bullet that matters it is the BEARING LENGTH of the bullet.
I don't understand the correlation in that.
Are you saying that a long bearing length requires less spin?
What about the difference between a .45 caliber cylinder and a .45 caliber round ball? The ball has a very short 'bearing length', but barely needs to spin to be stable...because it's overall length is so short.
For example:
The .45 MaxiBall is about an inch long, and the bearing length is almost the same length. It needs a 1 in 48 twist.
The round ball only needs a 1 in 72 twist, and it's bearing length is about 1/8".

A quarterback with wide fingers gets a longer 'bearing length' on a football than a skinny-fingered guy. But both have to spin the ball at the same speed to make it stable.

The bearing length could be important in how solid the rifling's grip is on the bullet, but the whole thing will spin at the same rate...and a long one must spin faster.

Going back to the 'top analogy'...
A tall skinny top needs to spin faster than a short fat one. But both get spun by a small half-inch segment at the top of the handle.
That is the 'bearing length' of those tops.

CM

[Larry Gibson]

Lead Melter....
think of the bullet as a gyroscope because rotational stability is what its all about.

Remember the gyroscope we all had as a kids.....when the rotational rate of spin was high the gyroscope was stable, as the rotational rate got slower and slower the gyroscope started to tilt until finally it fell over....
For boolits the rate of twist is what is important, not the straight line velocity....the straight line velocity is not important to bullet rotational stability

for example.....a 1:12 rate of twist will rotate the bullet 1 revolution for every 12" of barrel length. No matter how fast (velocity) the bullet is traveling down the barrel it will never rotate any faster than the rate of twist !!!
As you increase the rate of twist, say 1:8 you are increasing the rate of rotation and imparting more rotational stability....

We simplify by saying that a faster rate of twist (1:8) will stabalize a bullet better than a slower rate of twist (1:12)

You can complicate matters be introducing such things as bullet shape (pointed vs blunt) and changes to the center of mass of the a bullet ....etc, etc.

BUT to keep it simple just remember the gyroscope and rotational stability.
I hope this helps


What you quote here is RSPD (Rate of Spin Per Distance). That is not the same as RPM (Revolutions Per Minute). In RPM the veloity equals the time and must be calculate. Since stability is quantified in RPM or RPS then the velocity must be facotred in.

Larry Gibson

[Larry Gibson]

Lead melter,
As I understand it, you get the best accuracy with enough twist that the bullet is just stabilized. Now with jacketed, going faster than this twist rate does little or no harm, because the bullets are pretty homogeneous, and the jackets are very concentric. With cast, however, there seems to be a sweet spot where the bullet is being spun fast enough to stabilize, but not so fast as to magnify the imbalances created by internal, therefore unseen, imperfections in the bullets.

I think if you were to go to the trouble of weighing your bullets, and discarding the lighter ones, as opposed to segregating them by weight range, you might see some improvement. The light bullets likely have internal voids or poorly filled out edges to the grooves, and while some of them might match the weight of other "light" bullets, the imperfections would hardly be uniform.

Bob K

I will measure a 311299 against a Hornady 220 gr RN when I get home (after the 24th). A 311291 (180 gr fully dressed) is shorter than a 180 gr SP bullet and the 311041 is shorter than Speer 170 gr FPs. We also must remember that a 180 gr RN is shorter than a 180 SP and both are shorter than a 180 SPBT.

Larry Gibson

[AZ-Stew]

KAF,

Centripital/Centrifugal

Thanks for the correction. Apparently I misremembered something from physics class 25+ years ago.

Regards,

Stew

[leftiye]

Simple answer is - no. The same rules hold for cast lead as do for swaged lead, or any other boolit. Length is the issue, and rpms are necessary to stabilize - more of them the longer the boolit.

This is a separate issue from boolits jumping the rifling due to torque exceeding metals's yield point. Where the confusion comes in is that with jacketed bullets twist used is much tighter than the minimum that will stabilize both lighter for caliber AND heavier for caliber boolits (short version - tighter twist than required). So some caster puts his long heavy, slow moving boolit in that tube and lo and behold, it still stabilizes the boolit. Then he wonders if cast boolits don't need as much twist as jacketed.

One factor that may be relevant here is that the slowest twist THAT WILL SUCESSFULLY stabilize a given barrel/boolit/load combination tends to be more accurate due to causing the least deformation of the boolit.

ATR, you are right, twist per distance is constant. But rate of revolving (rpms) goes up as velocity does (boolit revolves/travels rate of twist in less time - voila, more revolutions per unit time) for any given twist. Revolving is what produces centrifugal (whatever) force, and this causes the gyroscopic effect that stabilizes the boolit.

[Lead melter]

Might be best just to do what my 'mountain man' type buddy would say..."Just shoot the damned thing and see what happens."

[SPRINGFIELDM141972]

+1 on the mountain man theory. I don't have the means to change barrel twist for a given boolit weight/lenght anyway. I have to shoot what I have soooo.... I shoot and see what happens.[smilie=1:

Regards,
Everett

[atr]

supermag is partially right.....
But, its has to do with fundamental law of the conservation of energy (basic physics).....

the energy we develop in our charge is now split into both rotational kinetic energy and translational kinetic energy. If the bore were completely smooth, i.e. no rifling lands then all the charge would go into translational kinetic energy....but since we do have rifling some of the total kinetic energy is now rotational which causes the translational velocity to be decreased.
However for the us the rotational kinetic energy portion of the equation is small ...so we just focus on the translational kinetic energy (muzzle velocity for a give weight bullet)

[Phil]

Here is the Greenhill formula. Greenhill was an Englishman whose primary study was the flight of artillery projectiles. He was regarded as foremost in his field during his lifetime.

I've used this formula for years, it works. It was originally developed for round (or blunt) nose lead bullets. For modern pointed jacketed bullets change the 150 to 175. It is simple to use.

Length divided by diameter = length in calibers

150 divided by length in calibers = twist in calibers

twist in calibers X diameter - twist in inches

That's all there is to it. Nothing to do with bearing length or lube grooves, just the length and diameter of the bullet. The result you get will be the MINIMUM twist for the bullet you plugged in.

Cheers,

Phil

[runfiverun]

finally this is getting the discussion it deserves.
except........
unless, you are trying to push the softer cast boolits to speed with accuracy, and not having to clean your bbl every 4 shots.....
i'll take the slower twist for that.....every time.

[Phil]

Hi runfiverun,

I agree with you about using the slowest twist with this caveat; my experience is that to get the most reliable results, especially for longer ranges (over 200 yards for instance) you should go one inch faster on twist than indicated by the Greenhill formula. The bullets are just more stable with a bit more spin when the range opens up a bit and the wind starts to blow.

I also agree that its good to finally get a discussion going on twist.

Cheers,

Phil

[runfiverun]

we have had......discussions on twist before.
it was called the rpm theory and went on for months.

[44man]

I have worked with every formula to predict twist rate needed and all are so far off from what actually shoots best it baffles the mind where they came up with such stuff.
Something to ponder--- does a longer bullet need more spin then a short bullet? Or is it because the spin rate can't be reached with a longer bullet because the velocity is lower in it's pressure range?
Could it not be true that ANY bullet needs to be spun in a very close range to each other and the twist depends on the velocity you can achieve with each bullet?
I have read where BR shooters change 1" in twist for weather conditions, would not a small change in the powder charge compensate?
I shoot BFR revolvers and all have FASTER twist rates then standard. My 45-70 has a 1 in 14" twist. I once shot 3 shots into 2-1/2" at 500 yd's with it! How in the world did THAT happen? I clang steel at 500 meters with consistency if I do my part yet I can't get anywhere near that at 200 meters with my 45-70 rifle that has a 1 in 18" twist.
My .475 has a 1 in 15" twist and shoots heavy boolits like crazy and will hold under 1" at 100 yd's depending only on ME. Shoot a .475 revolver with a 1 in 18" twist and heavy boolits are a pain, the gun will love a 350 gr boolit better. Can it be velocity is limited and spin can't be brought up enough?
Now look at the .44 Marlin with the 1 in 38" twist, (Figured from Greenhill by a pencil pusher.) Biggest piece of crap ever made! :groner: Beyond 50 yd's it is just luck to hit anything. Marlin broke down and changed the .444 to a 1 in 20" because even it could not reach the velocity needed to spin up a heavy boolit for long range.
Anyone that follows predictions as to what twist is needed will be sadly disappointed! Nothing works but actual shooting and testing with each gun and bullet.
Even back in my varmint hunting days, the .220 Swift far outshot the .22-250 at long range because it had a faster twist and could shoot heavier bullets. 600 yd's was duck soup.
I will choose a little faster twist every time! Easier to work with.

[joeb33050]

One small correction for all of us to remember when comparing cast to condom bullets. It is not the length of the bullet that matters it is the BEARING LENGTH of the bullet. Condom bullets tend to have a lot of the bullet length that does not bear on the rifling. As much as one third of the length may not bear.

This is rare in lead boolits. We usually have most if not all of the length of the boolet bearing on the rifling. Thus when using something like the Greenhill formula you must use the Bearing Length of the Boolit/bullet as your variable.

I don't know this and can't remember ever hearing it before. Could you give me the source?
Thanks;
joe b.

[44man]

I don't know this and can't remember ever hearing it before. Could you give me the source?
Thanks;
joe b.
I have been beginning to wonder if bullet length or bearing length has anything to do with it at all. Could it just be bullet weight?
Some say a solid copper bullet is longer so it needs a faster twist but has anyone PROVEN that? Maybe the added friction has something to do with it. Lower velocity from friction, less spin!
I think this rate of twist problem needs a whole new fresh look.

[felix]

More twist is required on the projectile when the projectile is more affected by the ambient. Therefore: Longer the projectile, the more the twist is needed; Conversely, the heavier (specific gravity) the projectile, the less the twist is needed. Summing up, a solid long copper projectile needs twist, whereas a short gold projectile would not care for much twist. Besides, and this is very important, a twist in a gun is meant to assure the twist is given to the projectile, and ALL formulas for twist require that is true. So, if a projectile is not spinning at a certain RPM as defined by the twist, the formulas are null and void. Velocity, in the velocity range we discuss for boolits, does not effect the results of the formulas mostly used. Given a generic muzzle velocity of 1400 fps is sufficient for all calculations when figuring twist requirements. ... felix

[Larry Gibson]

we have had......discussions on twist before.
it was called the rpm theory and went on for months.

The twist and thus the velocity and RPM required for stabilization (this threads topic) required of cast bullets is different than the RPM threshold regarding cast bullets. Not the same topic at all.

Larry Gibson

[Boz330]

Here is a site that all you have to do is plug in the numbers. It is aimed at BP but many of the cast loads are close. With BP this table is spot on in my limited experience. There are dynamics that affect the boolit when it is in the trans sonic area and if your target is there your results will drive you crazy. Good before and after but not there.

http://www.uslink.net/~tom1/twistrate.htm

Bob

[felix]

Tom's formulas are too sensitive to velocity for small bores. ... felix

[runfiverun]

larry:
i think it is tied together,as the original question was about boolit length and stabilization.
and how it relates to cast versus jacketed.
and what we are mostly dealing with is factories hedging their bets to make bullets stabilize[or over stabilize] no matter what.
and we need something a bit different to achieve velocities with cast boolits and hold accuracy at those levels.
now 44 man is showing that with the lower velocities of his hand guns he needs a faster twist to achieve stabilization.
ain't no wonder it's hard to agree on the subject.
a is shooting a 200 gr boolit in a 0-6
b is using a 130 gr boolit in a 308 and
c is using a 400 gr boolit in his sharps.....

[Larry Gibson]

runfivrn

I don't see that the two are tied tgether at all. Bullets reach the RPM necessary for stabilization far below that RPM of the RPM threshold. The adverse affects of the RPM threshold are when the centrifugal force over comes the rotational stability of the bullet. If the bullet is not stabile to begin with then there is no accuracy to begin with because there is no rotational stability.

Larry Gibson

[44man]

Here is a site that all you have to do is plug in the numbers. It is aimed at BP but many of the cast loads are close. With BP this table is spot on in my limited experience. There are dynamics that affect the boolit when it is in the trans sonic area and if your target is there your results will drive you crazy. Good before and after but not there.

http://www.uslink.net/~tom1/twistrate.htm (http://www.uslink.net/%7Etom1/twistrate.htm)

Bob
I punched in a bunch of stuff and it still reads way too slow of a twist to make use of. For instance, using the RD boolit out of the Marlin, it says I need 1 in 33.5". It is a known fact that the gun will not begin to shoot until a 1 in 25" twist is used and a 1 in 20" would be better for a heavier boolit.
I don't think there is an equation on earth that is right. I don't think one will ever be right!
I think the Marlin needs a round ball to make it work! :bigsmyl2:

[runfiverun]

larry...... i think you just defined it right there
i would think that with velocity in the same bbl. [talking 308 10 twist] one would easily be able to reach both ends of the spectrum under and over-stabilized.
it then becomes an issue of velocity.
or am i all jacked here???
or should i be able to stabilize a 200 gr boolit at 850 fps, how about a 100?

[44man]

larry...... i think you just defined it right there
i would think that with velocity in the same bbl. [talking 308 10 twist] one would easily be able to reach both ends of the spectrum under and over-stabilized.
it then becomes an issue of velocity.
or am i all jacked here???
or should i be able to stabilize a 200 gr boolit at 850 fps, how about a 100?
Finally someone making sense! Use a twist that you can work with instead of one good for only one thing. We are not all BR shooters shooting one distance with one bullet.

[montana_charlie]

I punched in a bunch of stuff and it still reads way too slow of a twist to make use of.
I tried it for my new paper patched bullet shot in a Sharps rifle.
Bullet length - 1.450" (a touch on the long side for this caliber)
Muzzle velovity - 1200 fps (a generic speed)
Groove diameter - .459" (a common dimension)

The result is damn close to the 1 in 18 twist found in most of these barrels today...barrels which are known to perform well.

Maybe the numbers you punched in aren't very realistic...
CM

[pdawg_shooter]

[QUOTE=joeb33050;471822]No. That's NO. Heavier = longer bullets in a given caliber require a FASTER twist to stabilize. NOTE that the twist given by any formula is the MINIMUM twist required to stabilize a bullet.
A 110 grain bullet might stabilize at 16" twist, a 220 grain bullet might require a 10" twist. 10" is FASTER than 16".



+1 Ya got it right....simple, isn't it!

[felix]

Denser bullets require slower minimum twist (Copper jacketed vs. lead vs. depleted uranium)
Faster bullets require a slower minimum twist, the effect of velocity is SMALL
Denser media through which the bullet travels requires faster minimum twist. Bullets that stabilize at 10,000 ft. may not stabilize at sea level and won't stabilize in water.
Some contend that the slowest twist that will stabilize a given bullet/load will yield best accuracy.
joe b.


So, this too is correct. ... felix

[44man]

Denser bullets require slower minimum twist (Copper jacketed vs. lead vs. depleted uranium)
Faster bullets require a slower minimum twist, the effect of velocity is SMALL
Denser media through which the bullet travels requires faster minimum twist. Bullets that stabilize at 10,000 ft. may not stabilize at sea level and won't stabilize in water.
Some contend that the slowest twist that will stabilize a given bullet/load will yield best accuracy.
joe b.


So, this too is correct. ... felix
Very true at close ranges because the boolit does not rotate around the flight path because of over spin. If you shoot 100 to 200 yd's you want the boolit to be asleep out of the muzzle.
This is what is wrong with the Marlin .44. It is accurate at 25 to 50 yd's but goes into the wobble phase after 50 yd's because the spin is too slow. The top is ready to fall over!
A little faster twist then what is needed to stabilize a boolit is best because loads can be worked for all conditions and elevations. Not so with a slow twist where you are just plain stuck with one load, one distance and one condition.
We have too much BR theory here when we are just shooters and hunters that can't utilize the tight restrictions needed for BR.
If you deer hunt with your 30-06 with a 12" twist and use 150 gr bullets, fine! Then you want to use 220 gr bullets for elk or moose and expect to get shots to 400 yd's, best take your slingshot instead. Funny the rifle makers decided a 10" twist is more versatile.
CM, that doesn't say it is right! I wish my 45-70 BPCR had a 1 in 16" twist. The 1 in 18" shoots the best with the short, fat 500 gr, round nose gov't boolit and long range stability sucks with long spitzer types.
I fitted my Browning with a 20X scope and have shot sub 1" groups at 200 yd's with some boolits but I can't hit the 500 meter ram unless by accident. I can WATCH boolits go straight down range until a certain distance where they veer off in any direction.
Do you REALLY believe all that printed stuff?
I have shot the round nose gov't boolit to 1000 yd's with better accuracy then I get with a long spitzer at 400 yd's.
Naw, give me MORE spin. I want spin downrange, not just at the muzzle.

[onceabull]

So,44man,you are telling us that Glen Fryxell's published work on the 444 M.with 300 gr.(and up) boolits and 1/38 twist is "artistic license", or ????? ???? ???..Onceabull

[Larry Gibson]

larry...... i think you just defined it right there
i would think that with velocity in the same bbl. [talking 308 10 twist] one would easily be able to reach both ends of the spectrum under and over-stabilized.
it then becomes an issue of velocity.
or am i all jacked here???
or should i be able to stabilize a 200 gr boolit at 850 fps, how about a 100?

Well, a 311299 over 2.7 r of Bullseye runs around 550 fps ('m not at where my data is so I'm taking this from memory) out of my 10" twist .308W as does 323471 over the same load out of a M9 24/47 with a 9.5" twist. I Also shoot Lee TL31-90-SWCs over the same load at 800 or so fps out of the .308W. All are stabilized and show very good accuracy out to 10+ yards. I've even shot the 323471 over a lesser charge at around 250-300 fps and it was stabilized and shot well at 50 yards.

It is well proven with regular cast bullets the RPM threshold will destroy accuracy long before the bullet reaches a stage of "over stabilization". Thus it is jacketed bullets you are discussing here. It is easy to shoot .30 cal j bullets of the longer VLD type at a low enough velocity that they do not stabilize in a 12” twist .308W but I’m not certain about a 10” twist one. It is also easy to shoot a lighter bullet fast enough in the 10” twist .308W to “over stabilize it”. We can drive 80-100 gr bullets *they are short and stubby) in 10” twists fast enough to over stabilize them yet bullets like 110 gr SP/HPs shot at the same velocity will still be stable at the same velocity.

Interestingly many believe there is a “perfect twist for each bullet of a certain design in each caliber. I am so far inclined to agree with that. During many of my tests I measure the actual BC of the bullets shot. I have found in shooting various bullets through 10, 11, 12 and 14” twist .30 cal barrels and .223 barrels of 7, 9, 12, and 14” twists that certain design types of certain weights like a particular twist better. For example; I have found the BCs of 165 to 180 gr BT bullets to be consistently higher in .30 cal barrels with 12” twists. The BCs of 125 to 155 gr bullets are always higher in the 14” twist barrel. The heavier 190 to 220 gr bullets give higher BCs out of the 10 and 11” twist barrels. The measure of the BC gives a measurement of the efficiency of the bullet moving through the air. Thus a higher BC means the bullet is better stabilized and is moving through the air more efficiently or to put it simply; the same bullets with a higher and more consistent BC better stabilized.

44Man's statements of bullets "veering off" at a certain point down range is quite correct if the twist is too slow and the stability is marginal to begin with. He does go off on "BR stuff" but his reasoning is not entirely at fault. If you are building a cast bullet rifle to shoot out to only 200 yards then best accuracy dictates a twist that provides minimal stabilization out to that range. However, if you are building a rifle to shoot longer ranges then you want a twist that provides complete stabilization across that range. You will not want the bullet to be under stabilized or over stabilized. The .444 Marlin was never designed for long range shooting. It was designed to give hunting accuracy with a lower trajectory to .44 caliber handgun bullets to 200 yards. Wanting to shoot a 300+ gr bullet at 500+ yards should not draw criticism to the Marlin but instead should draw it to the user who is using it out of it's design parameters. Also the 45-70 was found to be very accurate at 1000+ yards with the RN 500 gr bullet with a 22" twist. Increasing the twist did not improve accuracy. Now some want to shoot longer spitzer shaped bullets and blame the 22" twist because it is inaccurate. The fault lies not with the 22" twist but with the use of it. Bottom line is a rate of twist must be used to adequately stabilize a chosen bullet over the distance it will be shot at. If using J bullets or a cartridge/cast bullet that will not exceed the RPM threshold then a faster twist is better (with in reason).

BTW; Many minimal stabilized bullets and over stabilized bullets still shoot well at moderate ranges. Minimal and over stabilization should not be confused with "unstabilized" bullets.

Larry Gibson.

[44man]

Very well said Larry! :drinks:
Onceabull, true that the .444 gives enough velocity and spin to make it a viable 100 yd shooter. With the smaller case of the .44 mag you just can't get enough velocity and spin to make it work past 50 yd's.
However Marlin was under a lot of pressure about poor performance so they changed the twist in the .444 while making excuses for the .44. They sent me ridiculous figures showing why it works, I have to wonder if they ever shoot the guns past the proof range?
Glen has done a lot of work, true, but he has more resources then the average shooter. I hesitate to say how much work the .444 took.
Marlin also screwed up saying the Ballard rifling was made for cast!!!!!. Groove depth is the same as micro groove at .003", actually less grip on a boolit then the micro groove.
No, I don't believe anything I read. What counts is sending thousands of boolits downrange myself. Watching boolits in flight is very revealing too.
It gripes me to no end that I can shoot the same size groups at 200 yd's with my .44 revolver that I do with a scoped Marlin .44 at 50 yd's. It also gripes me that a 45-70 revolver shoots better at 500 meters then my BPCR. I even kept 4 out of 5 shots on a 6" swinger at 400 yd's with my .475 revolver.
I tend to think someone has it wrong but Magnum Research has it right. Ruger has it right with the .44 but puts the wrong twist in the .480 so only light boolits shoot good. Freedom puts the wrong twist rates in some calibers---too slow, light boolits only.
Now most of you have seen this group I shot with my Ruger .44 and a 330 gr boolit to measure drop at 200 yd's. I shot three and they were in 1-5/16". PLEASE someone show me they can do that with a marlin and I will bow down to you! :Fire:

[runfiverun]

this last page has probably some of the better information out there regarding twist rates.
the more you want a rifle to do one thing the more specialized it becomes.
there is nothing wrong with that.
but i have learned to become a bit more picky concerning factory rifles when it comes to shooting cast through them.
and twist rate is one area i pay attention to.
in fact the next rifle i buy will be a partial custom with a bbl i order just for cast shooting.
will it be able to shoot jacketed also?
might be a good varmint rifle too........

[405]

I fitted my Browning with a 20X scope and have shot sub 1" groups at 200 yd's with some boolits but I can't hit the 500 meter ram unless by accident. I can WATCH boolits go straight down range until a certain distance where they veer off in any direction.


Yes,
The last time that happened to me I was shooting a twist that SHOULD have easily stabilized the bullet I was shooting at the velocity it was going to any practical range for the set up. But, as you described, I too literally watched the bullets veer wildly at about 200 yards. We're not talking veering a few inches on paper but so much that I could easily see them do it as the recoil settled! They were randomly taking a side road several feet off course at about the 200. I'm a believer... just can't fully understand it. :veryconfu

[missionary5155]

Good morning
Just a note on the historical side of this... Mr. Greenhill was working with artillery projectiles. I may be incorrect BUT I do not remember reading he ever stated his formulas were to be applied to small arms.

Does anyone KNOW if projectile rotation slows equaly to FPS ?
Thanks everyone... makes for interesting reading.
Mike God Bless you...

[Larry Gibson]

.....Does anyone KNOW if projectile rotation slows equaly to FPS ?
...

No it does not. The rotation (RPM) of the bullet slows very little over the flight of the projectile.

Larry Gibson

[Larry Gibson]

......the more you want a rifle to do one thing the more specialized it becomes. ....... in fact the next rifle i buy will be a partial custom with a bbl i order just for cast shooting.
will it be able to shoot jacketed also?
might be a good varmint rifle too........

Many believe that the slower twists are specialized.
Actually they are not. A 12" twist in a .308W stabilizes bullets up through 200 gr just fine. An '06 with the same 12" twist stabilizes bullets up through 220 gr just fine. A 14" twist in a .308W stabilizes cast bullets up through 180 gr (haven't tested a 311299 at 200 gr in it yet) just fine and also jacketed 180 gr RNs and even M118 174 gr FMJBTs quite well. We also know the 16" twist of the .32 Special stabilizes 170 gr bullets quite well out to the practical range of that rifle.

It would seem the 10" twist is still (hold over from shooting 200 gr RNs in the 30-40 and 1903 cartridges) the "standard" for most .30 caliber cartridges. Yet tests prove the 12" twist to give better accuracy over a longer spectrum of range because the bullets have better rotational stability and higher BCs. The military did considerable testing before adapting the 7.62 NATO. Standard twist for it is 12". Winchester also made its 30-30 and .308W barrels with 12" twist. Savage knew the 12" twist was the better for the 30-30, the .303 and the .300 Savage. Huskvarna even knew this and also made it '06 with a 12" twist. Weatherby .300s are 12" twists.

There is really little need for the over stabilization of the 10" twist in most .308W, the 30-06s, the .30 cal magnums when a 12" twist would be better. This is particularly true ith the 10" twist that was standard in Marlin 30-30s for years. Factories stuck with the 10" twist not be cause it was the best twist but because it worked ok in most .30 cals and it expidited less costly production or purchase of barrels.

Thus a "specialized" twist for cast bullet shooting most often will work just as well with jacketed bullets of common useage with that cartridge. If one is wantig to buy a rifle for cast bullet shooting mostly then I always suggest buying a used rifle and having it barreled with an appropriate twist for the range of cast bullets you want to shoot in a particular cartridge. The results will be better accuracy at a much higher velocity and a much happier cast bullet shooter.

Larry Gibson

[leftiye]

Quote:
Originally Posted by missionary5155
.....Does anyone KNOW if projectile rotation slows equaly to FPS ?
...

No it does not. The rotation (RPM) of the bullet slows very little over the flight of the projectile.

Larry Gibson

I really think this deserves a little more attention. I'm neither inclined nor in possession of info to say that rpms do abate with distance. However, as boolits seem to lose stability as they lose velocity, one should be asking why as pertains to this phenomenon. I.E. if the rpms are still there that are necessary to stabilize the boolit, why don't it stay staybilized? Is it just the lack of energy that lets it be deflected (NOT a good guess - there's less buffeting with the reduced velocity and resulting less air resistance).?

[runfiverun]

leftiye i think the momentum of the boolit over comes the stability.
when we..larry[,i think larry did too[ bass,and i all shot the test last year about linear group size.
we all ran into nearly identical groups. and problems, at identical distances. and near identical velocities.
we all were using 10 twist rifles, but on vastly different platforms and sightig systems.

[leftiye]

R5R,
Can you elaborate on that a bit? I took the aforementioned test to be the fault of Larry's chosen boolit - it being a poor design for high velocity - going completely haywire due to deformation. In the present issue we're talking about low velocity, and the fact that rpms should still be very sufficient to stabilize the boolit. BTW, low velocity = low momentum.

[Larry Gibson]

leftiye

"I really think this deserves a little more attention. I'm neither inclined nor in possession of info to say that rpms do abate with distance. However, as boolits seem to lose stability as they lose velocity, one should be asking why as pertains to this phenomenon. I.E. if the rpms are still there that are necessary to stabilize the boolit, why don't it stay staybilized? Is it just the lack of energy that lets it be deflected (NOT a good guess - there's less buffeting with the reduced velocity and resulting less air resistance."

The bullets at longer range when velocity drops become over stabilised and other things, such as precession, begin to radically effect stability. Why do some bullets "go to sleep"? The answer lies most often in a minimally stabilized bullet with some yaw and wobble becoming fully stabilized as velocity drops but the RPM remains the same. In other words; stabilization increases as ange increases and velocity drops. As velocity drops below a certain level for a certain stability then other factors cause precessions which cause the bullet to radically become destabilized and it flies "off into never, never land" as observed by 44Man.

Larry Gibson

[Larry Gibson]

R5R,
Can you elaborate on that a bit? I took the aforementioned test to be the fault of Larry's chosen boolit - it being a poor design for high velocity - going completely haywire due to deformation. In the present issue we're talking about low velocity, and the fact that rpms should still be very sufficient to stabilize the boolit. BTW, low velocity = low momentum.

Sory leftiye, but my "chosen bullet" (311291) was obviously not "selected" as a bullet for high velocity. It was selected because it is "the" representative .30 caliber bore nose riding cast bullet used by mmore cast bullet shooters than any other. My tests along with Bass's showed that very respectable accuracy was obtainable up into the 2300+ fps range out of 3 different 30-06 rifles. Perhaps you just missed that part.

Accuracy did deteriorate to a degree (di not go "haywire" though) through minimal deformation during accelleration to high velocities. And guess what caused that? The bullets exceeded the RPM threshold and the centafugal force of the higher RPM had the adverse affect on said "deformation". Thank you for pointing that out:-D

Larry Gibson

[runfiverun]

i was using the rcbs 165 silh boolit and at some point after 200 yds with the higher velocity i lost stabilization also.
iirc i could only find 3-4 boolits on a 4'x4' paper out of 10 shots.
with the velocity lowered into the "threshold". i was able to shoot 5-6" groups and could hit bowling pins with regularity.
part of the larger groups were caused by my hunting set-up 3x9 leupold scope and mirage.
the holes i did find at higher vel were still round,but the dispersion had to be caused by "something", described by 44 man,and somewhat by larry.
i don't really know what to call it, but i think the boolit just starts off in a direction[slightly] and the forward momentum just carries it that way.

[Larry Gibson]

Runfiverun

I'll bet the few holes you found showed the bullets flying point on and had you found the others you'ld have found the same. Point being; the bullets did not lose stabilization (they would have keyholed or showed some signs of it). More likely at the higher velocity over the RPM threshold the bullets flight path was changed by the precession caused by the centrafugal force of the higher RPM. That centrafugal force overcame the rotational stability of the bullets causing them (as a precession effect) to fly radically off course. That is what happens. I know a lot of folks (a few in particular) don't have the background knowledge of ballistics to understand that. That is what causes a lot of confusion, simply a lack of understanding. Notc alling anyone dumb here or insulting anyone, just stating where the confusion lies.

Larry Gibson

[44man]

This is hard to say! The BPCR makes a good study though. The worst boolits to stay on path are the very long ones with a shorter drive band length then short, stubby round nose boolits. Since velocity is sort of fixed in any BP rifle, there is little to be done to speed up any given boolit, the same as a revolver where case size limits what you can get.
The only way to get a velocity increase with BP is to increase case length and use the same weight boolit. Now in a revolver, the same thing holds true although most increases in case length or diameter is done to increase boolit weight without a change in velocity except for calibers like the .460, developed for speed with a light bullet.
Anyway, every time I lengthened the nose on my BPCR boolits, stability went to pot at long range. Since most increases in length also result in a weight increase, it comes with a velocity and spin loss too, never to be exceeded.
Now, is it the longer boolit by itself, the longer nose, the loss in velocity or the loss of spin? Or a combination of all? Could it be they knew what they were doing when the 500 gr gov't round nose was developed and we make a mistake trying to flatten trajectory with a long, pointy boolit without any way to increase velocity? And spin?
I have to look at my revolvers too. I have read 100,000 times that a WFN goes unstable beyond 50 yd's and the WLN is a little better, the semi-wadcutter is even better. Completely untrue!
The very worst accuracy from any revolver I own or ever owned was with Keith boolits. Well, they do hit the target but thats all I can say about them. As the same weight boolit gets shorter and the drive bands lengthen as in a truncated cone design, stability is increased and groups at all ranges have shrunk. I have shot hundreds of groups at 100 yd's at or under 1" and can hit pop cans at 200 yd's with a WFN.
You realize too, that my most accurate revolvers are the BFR's WITH MUCH FASTER TWIST RATES THEN ANY OTHER REVOLVERS. How many of you own a 45-70 rifle with a 1 in 14" twist rate? I was concerned because the gun loves a 300 gr bullet and my 317 gr boolit. But by working with it, I have not seen an accuracy change with over a 100 gr weight change. The velocity range I use is very close over the whole weight range with only a small loss at the accuracy point for each boolit. I have worked with boolits from 300 gr to 448 gr without much change in accuracy even at very long ranges. I have never before owned any revolver that will shoot any boolit I stuff in it---EXCEPT a Keith boolit of any weight. They shoot the same size groups at 25 yd's as my other boolits do at 100 yd's. Ditto my .475 and my RSB .44.
Now the 45-70 BFR shoots best at about 1632 fps but I have gone to 1800 fps while testing without a huge accuracy loss although I never tried the very high velocities at long range.
You fellas can talk all kinds of fancy math, precession, wobble, too much or too little spin and theory all over the board but when I watch a WLN or WFN go a perfectly straight line (Not counting any wind drift or drop.) to 500 meters from a revolver and hit steel, using the proper hold over and wind allowance, my theory is to give up the formulas and just find what your gun likes by shooting.
I agree with Larry that there is a point where a boolit will spin itself to pieces but my question still is--WHY? When the accuracy point has long been surpassed.
If a boolit does not shoot good at any velocity even after it blows up, get rid of it! The same way I put the Keith molds way in back of the drawer! :bigsmyl2:

[44man]

Runfiverun

I'll bet the few holes you found showed the bullets flying point on and had you found the others you'ld have found the same. Point being; the bullets did not lose stabilization (they would have keyholed or showed some signs of it). More likely at the higher velocity over the RPM threshold the bullets flight path was changed by the precession caused by the centrafugal force of the higher RPM. That centrafugal force overcame the rotational stability of the bullets causing them (as a precession effect) to fly radically off course. That is what happens. I know a lot of folks (a few in particular) don't have the background knowledge of ballistics to understand that. That is what causes a lot of confusion, simply a lack of understanding. Notc alling anyone dumb here or insulting anyone, just stating where the confusion lies.

Larry Gibson
Watching a high power rifle boolit is next to impossible but BP boolits can be watched. Precession should alter the flight path the same for every shot. This is not the case I see. The boolit can go in any direction and the hits at 500 meters are in a large circular pattern, low, high, left and right, the full 360* of a circle. I can detect no actual strange actions of the boolits and no actual change in the orientation, points seem to be going in line with the POI. Depending on the boolit, the range this starts changes and they transition from a nice straight path and just widen in any direction without regards to wind direction or strength. I compare it to a full choke shotgun where the pattern is tight for a certain range, then widens quickly as range increases.
I have no idea if it is related to a subsonic transition or not. Most of these boolits only start at 1050 to 1200 fps at the muzzle. The sudden widening starts at about 350 to 400 meters.
What happens after 500 meters? Will they start to turn and keyhole? Some boolits I have, have gone straight and hit targets at 1000 yd's. They were always the shorter boolits with short noses. My opinion is that I have run out of enough spin with the long boolits. A few thousand RPM's.
I just don't think you can say as the boolit velocity drops, the spin is then too great for stability because the spin dropped less then the velocity. I will not buy into that! If the spin is too great you see a precession around the flight path at close range, I never see that at long range.

[montana_charlie]

This is hard to say! The BPCR makes a good study though. The worst boolits to stay on path are the very long ones with a shorter drive band length then short, stubby round nose boolits.
I have heard you state that a few times, and I don't say much because I am not up on RPM's versus RPI (revoltions per inch). I don't worry too much about velocity variations because (as you say) the range is pretty small in BPCR.

But, look at these bullets. Note the shape and length of the noses. Evaluate them for me (us) using your belief that long, slender noses aren't good in long range bullets.

This one, launched at 1300 fps by guys shooting 45/70 rifles with 'standard' 18-inch twists, has been doing well at 1000 yards for a couple of years, now. You could almost say the the entire 'bearing length' is confined to the last three driving bands.

http://castboolits.gunloads.com/picture.php?albumid=88&pictureid=461

This one, with almost the same nose, is stable (and accurate) at ONE MILE. Depending on how you look at it, the nose is actually .900"...well over half the total length...and you could almost add the next two bands to that.

http://castboolits.gunloads.com/picture.php?albumid=88&pictureid=462

CM

[Larry Gibson]

44Man

In your one post you answer your own question as to why you get the results you get; “that my most accurate revolvers are the BFR's WITH MUCH FASTER TWIST RATES THEN ANY OTHER REVOLVERS.” The revolvers you use have fast enough twists to stabilize the bullets. It is well know that in S&W .38 Specials with 18.5” twist barrels that WC (about as wide a WFN as you can get) do lose stability past 50 yards when kicked off by standard target loads like 2.7 gr Bullseye. It is also known that the very same loads in Colts with 16” twist barrels stay accurate to 100+ yards. The reason is as we’ve discussed.

Now, as to the second post and a further discussion of stability and a loss of accuracy at longer range as you describe. Let us consider a gyroscope of sorts; the common toy top. Bullet stability is the same as the top. In this case let’s say our top is stabilized and spinning smoothly. Let’s observe the point of the top spinning on the floor is the point of the direction the bullet is going and the line of departure trajectory. Now we are going to gently touch the top on one side. This will be very gently so as not to cause wobble or certainly not to knock the top over.

Notice what happens to the top; the point of the bullet (the direction of bullet travel) moves slightly away from our touch, curves slightly and then stops some distance (may be small or large depending on RPM and the force of our touch) 90 degrees to the right of the direction of our touch. Our “touch” was a “precession” force. A precession force always will result in a 90 degree movement of the gyroscope (in this case our top) to the direction of the applied force. Now we can see the movement in a slightly elliptical path as it reacts in a 90 degree movement to the applied precession force. Also remember if out top was a bullet it would also be moving forward. If the precession force was applied to the bullet prior to reaching the target it could then hit the target anywhere along that path where the target was.

Also keep in mind that we only momentarily applied the force with a gentle touch. If the bullet were imbalanced then the force is continually applied. The bullets path is then one of a continuous elliptical path which is ever widening as the range increases. In the case of the RPM threshold the recession is when the increased centrifugal force of the higher RPM over come the rotational stability of the bullet. This does not mean the bullet is unstable and tumbles off somewhere. It means the rotational stability (gyroscopic effect) of the bullet is effected by the precession force of the centrifugal force of the RPM. The bullet (gyroscope/top) reacts by moving in an elliptical move 90 degrees to the right. The problem is this precession force is continuous so the bullet continues in an ever enlargement (non –linear) in group size as range increases.

Since the precession happens with each bullet when it will (velocity shot to shot varies as does the individual imbalance of each bullet) it does not “alter the flight path the same for every shot”. This is exactly why you see “Depending on the boolit, the range this starts changes and they transition from a nice straight path and just widen in any direction”. That is the way it happens.

BTW; in high power shooting it is very easy to follow the “trace” of the bullet and see the exact same thing.

Larry Gibson

[Larry Gibson]

Montana Charlie

Original twist for the 45-70 was 1-22". Those bullets syou show don't shoot for beans in that twst at 500 yards let alone 1000 yards...as 44man says. That's my "evaluation" for you based on considerable shooting with original and replica trapdoors with 22" twists.

It was the advent of those bullets for target shooting that led to the increased twist rate of 1-18". The 18" twist was necessary for those bullets to shoot well and remain stable at 500-1000 yard shooting. The 18" twist may be "standard" now, especially for target shooters. It was not "standard" at one time, the 1-22" twist was and was intended for 400 and 50 gr RN bullets. That twst does shoot those just fine to 1000+ yards.

Larry Gibson

[montana_charlie]

Montana Charlie

Original twist for the 45-70 was 1-22". Those bullets syou show don't shoot for beans in that twst at 500 yards let alone 1000 yards...as 44man says.
I would not be surprised to learn that is true...would even predict the same thing.
But, both of those bullet designs are less than two years old, while an 18-twist has been 'standard' for the forty-fives for much longer than that...probably dating back to the advent of the Postell design.

What 44man said is that (with a bullet of a given length) a short, blunt nose will remain stable at long range...while long, slender noses won't.

As a matter of fact, he is an advocate of fast twists...faster than 'standard' in most cases. Even the 18" is too slow for his liking.

One of his statements said, "I wish my 45-70 BPCR had a 1 in 16" twist. The 1 in 18" shoots the best with the short, fat 500 gr, round nose gov't boolit and long range stability sucks with long spitzer types."

And, "I shoot BFR revolvers and all have FASTER twist rates then standard. My 45-70 has a 1 in 14" twist. I once shot 3 shots into 2-1/2" at 500 yd's with it! How in the world did THAT happen? I clang steel at 500 meters with consistency if I do my part yet I can't get anywhere near that at 200 meters with my 45-70 rifle that has a 1 in 18" twist."

And, finally, "It also gripes me that a 45-70 revolver shoots better at 500 meters then my BPCR."

As you can see, the part of this discussion I wish to have with 44man is related to 'bullet nose shape'...and considers factors that don't really apply to an 'antique' with a 22" twist.

CM

[44man]

Good explanations Larry. Those are nice looking boolits and the one I am starting to work with right now is almost identical to the lower boolit except it is only 1.350" long. It shows promise so far.
I have a mold Dave Farmer made me just for the Browning and it shoots very good. It is 1.355" long with the nose pour flat. It too is almost the same shape as the lower boolit.
The one giving me to most trouble is 1.455" long, also the Lee pointy boolit (459-500-3R) will not shoot at all for me. I call it the air force boolit--wild blue yonder!
Now the top boolit looks better because it can be seated out, increasing case capacity so 1300 fps is easy to get, maybe even more. More spin? (But will it work in a Browning?)
What some of you are failing to see in what I have been saying is not from drastic changes in boolits. A very subtle change in nose shape or length can turn a boolit into a long range looser real fast.
My problem is compounded by the shallow, eight lands and grooves in the Badger barrel combined with almost no throat in the chamber.
Now all in the know say that the rifling in the Browning will not shoot a long bore ride boolit. The 500 gov't has a long bore ride and a short drive length. It is 1.260" long with a drive of .545". For some strange reason it shoots about the best. It also shoots great from an original trapdoor.
Now a very funny thing happened with my friends trapdoor. I tried my 317 gr BFR boolit in it with a load of 3031. I shot 10 shots through a tiny ragged hole at 50 yd's. However the POI was too far away from the fixed sights so we had to use the gov't boolit for his deer hunting, it was dead on. So in my estimation, the slower twist loved the lighter boolit. We both stood around scratching our heads over the accuracy from such an old gun! :grin:
I have made about 20 molds for my Browning and have not hit the perfect boolit yet. I believe the reason is that I listen to all the experts, trying too long a boolit, shorter bore rides, longer drive lengths, sharper points, and everything in between EXCEPT to try a shorter boolit.
This year I am going to load it like a Marlin micro groove, .451" bore ride and a .464" main section in a bore that is a little over .459". Here is the boolit.

[montana_charlie]

the Lee pointy boolit (459-500-3R) will not shoot at all for me. I call it the air force boolit--wild blue yonder!
That 3R Lee seems to cause problems for most who try it at longer ranges.
You only rarely hear someone say differently. I can't even guess what it's problem is. Maybe it's just too pointy...leaving too much of it's weight in the butt.

But...if you have formed your hypothesis about the difference in long range stability by comparing the Government bullet with the Lee 3R...it's no surprise you came out where you did.
CM

[Larry Gibson]

Montana Charlie

Keeing it in context with this thread 44man is using the 45-70 in his BFRs, which have shorter barrels than most BPCRs (unless he is really into the Buntline thing!). Shorter barrels mean less velocity. Less velocity means less RPM. Less RPM means a faster twist is neded in the shorter barrel to compensate for the less velocity/RPM. In other words; with a given bullet he needs a faster twist in his short barrel to get the same stabilization as you would with a longer barrel.

44man's statement; "I wish my 45-70 BPCR had a 1 in 16" twist. The 1 in 18" shoots the best with the short, fat 500 gr, round nose gov't boolit and long range stability sucks with long spitzer types." might very well be correct. He probably does need a faster twist than 18" to stabilize the spitzer type bullets at the lower velocity he is shooting them at. No if he is getting 1300 fps with them then it is also possible other things come into play against him. Because of the shorter barrels he must have a higher acceleration rate. The rifling of the Badger barrels may not be conductive to best accuracy as he mentions.

I'm not sure from his posts whether he is talking about using the spitzers in his Browning or his BFRs. I thought the Brownings had 18" twists? His 2 1/2" group at 500 yards caught my eye too but then I noticed the "once". I've shot as I'm sure you have too lots of 3 "shots" that were within 2 1/2" at 500 yards. He happened to shoot 3 of those "shots" consecutively is all. Random probability is all it is. I doubt he can do it on demand. Be really great if he could though. Wish I could do it at 100 yards with my revolvers. None the less I don't doubt he is a very good shot with his revolvers as he really works at it. As a matter fact because of his contnuous harping on the subject I've finally mounted a "red dot" sight on my Ruger Bisley .41. Hoping to try it out this next week. Hell, I might sneak in one of those 2 1/2" groups at 100 yards, I'll be happy with that:-)

Larry Gibson

[Lead melter]

You fellas have done your homework on this topic..that much is obvious. And just like the "Ford-Chevy-Dodge" debates, each person has his own ideas of what works and what happens and why. This is good and the way it should be.

But just to throw another cat into the bag, I was looking at some info on the Ranch Dog forum and came across another tidbit of info having to do with the center of balance and center of mass of the boolit. Do you suppose this aspect would have anything to do with the RPM threshold, stability issue vs. boolit design?

The reason I ask this is that a spear must usually be heavier at the head than at the rear if stability is to be reached, ergo, the stone or steel point is attached at the head. In the past I have read that some jacketed bullet designers put the center of mass in the rear of the bullet in order to make it function properly...just another thing I don't quite get.

[leftiye]

"In other words; stabilization increases as ange increases and velocity drops." Larry Gibson

The evidence seems contrary to this Larry. More rpms being required to shoot longer distances would say that boolits become less stable and require more twist as range increases. This from previous posts here in this thread (and other places). The boolits may be overstabilized as velocity drops, but this also is illogical, as the rpms are still there, and stabilization should be distinct from velocity. As 44Man said, precession would be predictable, what we're talking about here doesn't seem to be.

I did not say that you chose the 311290 for high velocity, I said it was a poor boolit for high velocity (and if groups going from 3 or 4 inches at 100 yds to 12 inches or so at 200 yds isn't going haywire, nothing is). (Reading comprehension needed.) However, this seems the correct place to say that these two phenomena might be the same one. Your boolit going haywire between 1 and 2 hunnert yards, and 44Man's .45s losing it at 200 yards. FWIW, unless the boolit is deformed, then this has to be a stability issue - n'est ce pas?

CM, I thimk the pertinent issue you're looking for may be stabilized surface rather than where the full depth driving bands are. You'll notice that both boolits you've shown do bear (in the case of the front bands, they ride the rifling) from the rear of the ogive on backwards. The unsupported portion of the nose is the culprit. Bore riding boolits get deformed very badly at higher acceleration rates, and go "haywire" therefore, while working well at lower velocities/pressures/acceleration rates.

[montana_charlie]

I'm not sure from his posts whether he is talking about using the spitzers in his Browning or his BFRs.
I am certain he has fired the Government bullet, and the Lee 3R, in his rifle. I assume it is the Lee that he is referring to when he says 'spitzer'.
He gets reasonable long range accuracy (from his rifle) with the round-nose, but not the 3R.

If he has the nuts to shoot 500 grainers from a revolver, he has probably tried both in his BFR. Since he mentions better accuracy from a fast twist, I assume that is talking about the 3R's (better) performance from a 14-twist revolver barrel.

As long as 44man continues to use 'BPCR' and 'BFR', I can keep up with him on which kind of firearm he is talking about.
CM

[44man]

Yes, Larry, the spitzers are in the Browning, I only shoot WLN and WFN from the revolver. No I can't shoot a small group on demand at 500 meters. I did it once trying to establish an aiming point over 26 feet up in a tree while my friend spotted. Once I hit steel, I took two more to confirm my aim point. However I was able to keep all the rest of my shots that day on the ram and that is something I have not been able to do with the Browning, sticks and the fancy sights. Stop and think of the error a red dot has at 500 meters just from the huge area it covers! I used the very bottom edge of the dot on a certain branch, it is amazing even the berm can be hit. I was also shooting Creedmore, no bags.
But I have no idea what the revolver is actually capable of at 500 meters because it would need a high power scope and a special base to raise the back of the scope a great deal.
How can a 10" barrel revolver with a red dot, flat nose boolits and a side of the leg rest shoot so stinking good?
And it is not just me! I hand the gun to my friends and it also shoots like that for them. I don't know how many times Pete slammed the ram. My other friends knock off pop cans and much smaller targets at 100 yd's, shot after shot from bags.
Another friend fell in love with my BFR and showed up one day with a new one and an Ultra Dot. I mounted it, sighted it at 50 yd's with my loads and swung over to an 1-1/4" piece of plastic paint can cover, one shot blew it off the stick it was on. I handed it back to a guy with the widest grin I ever seen! :drinks:
No fellas, IT IS THE GUN ITSELF! Larry, I could have you shooting Necco wafers at 100 yd's! I do not take credit other then for my loads.
The Browning is like the Marlin .44--- The barrel SUCKS! :brokenima
If I had money, both would be sporting new barrels.
The very worst thing I have found about my BFR revolvers is that my boolit boxes go empty so fast I can't cast enough to keep up. I am presently out of everything! :roll:

[Larry Gibson]

leftiye

The evidence seems contrary to this Larry. More rpms being required to shoot longer distances would say that boolits become less stable and require more twist as range increases. This from previous posts here in this thread (and other places). The boolits may be overstabilized as velocity drops, but this also is illogical, as the rpms are still there, and stabilization should be distinct from velocity. As 44Man said, precession would be predictable, what we're talking about here doesn't seem to be.

Precession isn't "predictable" regardless. How do you know exactly when that is going to happen down range? You don't. Not any more than a bullets time of flight hitting 1" left of another bullet at 100 yards is measureably longer let alone meaningful. (your concept, not mine) Now I suppose just because 44man says precession is predictable it is, eh? Sorry but it's not. Hang your hat on another argument, I won't even go off on this tangent with you. Bullets do become more stable as range increases if we are talkng about rotational stability alone. However we are not. There are other things that factor in to it.

If a bullet is stable at 140,000 RPM at 2000 fps then when it slows down to 1200 fps and yet the RPM is still 140,000 is it more or less stabilized? If that same bullet can be shot at 300 fps and be stabilized at 21,600 RPM then is not 140,000 RPM a little "over stabilized"? If that same bullet was shot at 1200 fps the RPM is only 86,400 RPM and it is stable, so is not the 140,000 RPM not "over stabilized?.

So leftiye, you tell us, other than "some one posted here or some other opinion can you provide any facts? Or possibly is it not just your usual argument you seek?.

I did not say that you chose the 311290 for high velocity, I said it was a poor boolit for high velocity (and if groups going from 3 or 4 inches at 100 yds to 12 inches or so at 200 yds isn't going haywire, nothing is). (Reading comprehension needed.) However, this seems the correct place to say that these two phenomena might be the same one. Your boolit going haywire between 1 and 2 hunnert yards, and 44Man's .45s losing it at 200 yards. FWIW, unless the boolit is deformed, then this has to be a stability issue - n'est ce pas?[/QUOTE]

No "reading comprhension" here. You failed to get your point across. What you said may not be what you meant but it is what you said. Just more bait for your usual arguement, sorry but I'm not biting.

Larry Gibson

[Larry Gibson]

montana charlie

Had to laugh, I think 44man is telling us how he really feels!

Larry Gibson

[Larry Gibson]

44man

You know, I am going to hold you accountable to get me shooting my Ruger right with that sight. I know it shoots my cast and particularly the XTPs really well. I am probably going to be bugging the doo doo out of you for info and assistance!

Larry Gibson

[BPCR Bill]

Google "Greenhill Formula". Some ingenious ballistician figured this out for us many years ago.

Regards,
Bill

[44man]

Google "Greenhill Formula". Some ingenious ballistician figured this out for us many years ago.

Regards,
Bill
That is the point I have been trying to make and maybe Larry is too. Greenhill does NOT work except in a very tight scenario like certain cannon rounds. It ALWAYS comes up with a twist so slow it will not work, so many are adding different figures to the formula so it agrees with what they are shooting. I could do that too and make it agree with a twist WAY TOO FAST! If I find a boolit that is stable at 2000 yd's from a certain twist, I can make Greenhill agree but greenhill as written will be wrong. You need a different Greenhill formula for every single bullet shot from one caliber and a different one for each caliber plus all the bullets shot from each. It is not proven from the mere fact that it must be changed to agree with what actually works. This is NOT E=MC squared!
Funny our military has gone to a lot of fin stabilized sabot rounds from tanks and such, using a smooth bore. I think they got tired of each different round needing thousands of corrections.

[Larry Gibson]

Larry, I can see that it is a waste of time to try to discuss anything with you. Either get on the subject, and ANSWER THE QUESTIONS THAT ARE ASKED or don't say anything, please.

Leftiye

That seems to be your standard line. You just ask rediculous questions which take up more time than the questions are worth. Why don't you, instead of asking questions, just tell us what the answers are to the questions already asked here? I suppose you'll come back with the usual "it's my position and I must defend it" garbage. However, many of us would like to hear you answer a question once, just once. Here's your chance. If you don't then I won't respond to your usually non-answers because you are only looking for another argument.

Larry Gibson

[405]

No point to make here. But, just thinking back on the previous long! thread on this subject I have often wondered about how the sonic/subsonic transition plays into all this. In a previous post on this thread I re-affirmed 44mans observation of bullets that suddenly veer off course. I can't say with certainty the exact range they did it when I watched them go wild but would estimate anywhere between the 150 and 250 yard mark. Given that plus the known that the bullets were leaving the muzzle at about 1250 fps seems possible this flight anomaly was happening about the time the bullets were dropping to subsonic???? Just a thought.

The specs for the "Wild One" described above are--- .440 bullet at 385 grs (11 BHN) with a shank support length of .580" and unsupported tangent ogive nose length of .520" at 1250 fps out of a 1:20 twist bore. Looking at a calculator the sonic transition happens just short of 200 yds.

As far as a proven design goes--- I know a .458 bullet at 438 grs (11 BHN) with a shank support length of .700" and unsupported tangent ogive nose length of .440" at 1250 fps out of a 1:18 twist bore is perfectly stable and extremely accurate to at least 600 yards.... likely much farther.

[felix]

Your thought is entirely possible, and probably very likely. ... felix

[44man]

Larry, I think precession is predictable, IF that is what causes boolits to go unstable. That is the big question. Now let us say it is the cause. Each boolit will be effected by it at a predictable distance although the direction the boolit decides to go is not.
The problem is that we are guessing and don't really know. I feel precession is the effect on an over spun boolit at closer ranges until it goes to sleep. The tail might move around while the point stays on track. That fits Larry's definition of touching a top.
A boolit DOES lose spin in flight although not as much as a velocity loss. So saying a boolit is spinning at 40,000 rpm's at the muzzle and is still spinning at the same rate at 500 meters is wrong. If a boolit NEEDS 40,000 rpm's to be asleep and drops to 35,000 over distance, it becomes unstable like the slowing top. This is the point outside influence will have the most effect, a gust can start it doing funny things. So is it REALLY precession?
BUT, I might be using the wrong word to start with! [smilie=1: Is precession the point when spin slows and the boolit becomes unstable? I have never found a suitable explanation in any dictionary that refers to anything but the earth in relation to the moon, planets and sun.
Let's start anew! If precession is the slowing of spin to the point a boolit becomes unstable, that point in distance is predictable for each different boolit but not on paper. It must be found physically. I know of no formula that says at which point spin will decrease enough for a boolit to start to wobble.
Lets go farther! If a boolit NEEDS 40,000 rpm's, does that change with velocity? I don't think so. I think that boolit needs the same spin at 3000 fps as it does at 700 fps. I don't think foreward velocity has any bearing on spin stability. Eventually we will discover they are two complete different influences, totally separate. Other then the velocity needed to start the spin in the bore.
So explain precession! Is it at the start or end of flight? I might be wrong as to where the definition of the word fits! :drinks:
I know where this is going! :mrgreen: I have some goofy ideas! I do a lot of spinning myself. [smilie=1:

[44man]

No point to make here. But, just thinking back on the previous long! thread on this subject I have often wondered about how the sonic/subsonic transition plays into all this. In a previous post on this thread I re-affirmed 44mans observation of bullets that suddenly veer off course. I can't say with certainty the exact range they did it when I watched them go wild but would estimate anywhere between the 150 and 250 yard mark. Given that plus the known that the bullets were leaving the muzzle at about 1250 fps seems possible this flight anomaly was happening about the time the bullets were dropping to subsonic???? Just a thought.

As far as design goes--- I know a .458 bullet at 438 grs (11 BHN) with a shank support length of .700" and unsupported tangent ogive nose length of .440" at 1250 fps out of a 1:18 twist bore will be perfectly stable and extremely accurate to at least 600 yards.... likely much farther.
Yes, very, very true IF the boolit is about to go unstable from a lack of spin or has slowed too quickly. Buffeting can be severe but like a jet coming down through the barrier, velocity makes the transition short and almost not felt. Come down through it by slowing too fast and the plane shakes and bangs. Noise at the ground is much worse too.
I do not see it with my revolver boolits and I know they are dropping subsonic down there somewhere.

[montana_charlie]

I don't pretend to know the ins and outs of 'RPM' and it's effect on stability...or inherent instability. But, I can spell Google.

Some of this seems to speak to the 'overstabilization' thing you guys keep hashing out.

" It is very important, in Match Rifle shooting, to minimize the instabilities that every bullet suffers in flight. Like a gyroscope, the bullet will yaw and precess as it spins on its way down the range. A certain minimal amount of this precession is required to keep the bullet 'tracking', keeping it pointing along its trajectory. If the bullet did not precess and went completely to sleep' then it would maintain its launch angle throughout its trajectory, which means that on the final part of the flight, when it is descending, it would still be pointing up, thus presenting a much larger cross section and substantially increasing drag. This is the extreme case of what happens when the bullet is spun so fast that the stability factor 's' is greater than about 3. The gyroscopic forces will prevent the bullet from tracking and the drag goes through the roof for the final part of the trajectory. If the precession is greater than that required to keep the bullet tracking then the result is again an increased effective cross section, giving increased drag and leading to disappointing ballistic performance."

It came from http://www.snipersparadise.com/ballistics/longrange.htm

CM

[felix]

Yeah, you gotta' see the egg shapes on target and notice the direction of the major axis. If up and down, it's what you have read. But, if it is crosswise, then that is the sign that the wind is trying to take over. Here is the baddie: If the wind is that bad, then you have to have that amount of rotation to remain on target. However, the concept of decreasing the drag is always good, but using rotation as the last resort. Accuracy always trumps impact velocity (at distance). Enter the concept of boattail to eliminate as much drag as possible in the downwards part of the trajectory. By the way, cast boolits do fairly well with a stability factor of 1.3 or so because of the ranges used. ... felix

[44man]

CM, exactly and is why we work loads. Can't spin too fast or too slow. The problem comes when the gun does not have enough twist to start with for the boolit you want to use and the velocity can't be increased.
That is why I want a little faster because I can use more types of boolits and if spin is too great for one, it is simple to reduce the load.
I worry less about drag then a boolit going unstable anyway. I think that is better then having a twist that only shoots one boolit at only one velocity.

[leftiye]

"That seems to be your standard line. You just ask rediculous questions which take up more time than the questions are worth. Why don't you, instead of asking questions, just tell us what the answers are to the questions already asked here? I suppose you'll come back with the usual "it's my position and I must defend it" garbage. However, many of us would like to hear you answer a question once, just once. Here's your chance. If you don't then I won't respond to your usually non-answers because you are only looking for another argument." Larry Gibson

Larry, If you don't like the questions I ask DON"T (YOU) RESPOND TO THEM! By all means, please don't! If you do respond to them - expect me or somebody to find fault with your reasoning and logic when it is faulty (which it usually is).

If you have trouble figuring out what's being asked, then that's probly a good reason to be still! Otherwise it's your job to be on topic and answer what was said to you, and asked of you, and to respond to the faults found concerning your response. Answering some peripheral issue and calling people names and slandering their intent isn't kosher, nor acceptable, nor productive, nor is it an answer.

I asked a valid series of questions relative to the topic that was being discussed. Questions that I hoped someone had some understanding of that I could benefit from. Your postulated explanation had holes in it. I said so, you took offense and became abusive. As usual.

[leftiye]

Beyond the above I want to thank 44man and 405, Montana C, felix, and all who have helped out above. I think 44Man has an expanation that fits the facts, and goes beyond that to accommodate other interfering factors too (say if the boolit goes subsonic for instance). I think that he is right that rpms do "wear" off a little due to friction with the air, and possibly due to yawing. Boolits may be losing stability if they are marginally stabilized initially, and lose rpms with distance. This subject is of great interest to me, my questions were genuine, and I am sorry for the unpleasantness that follows whenever I ask a question when Larry is around.

[44man]

Beyond the above I want to thank 44man and 405, Montana C, felix, and all who have helped out above. I think 44Man has an expanation that fits the facts, and goes beyond that to accommodate other interfering factors too (say if the boolit goes subsonic for instance). I think that he is right that rpms do "wear" off a little due to friction with the air, and possibly due to yawing. Boolits may be losing stability if they are marginally stabilized initially, and lose rpms with distance. This subject is of great interest to me, my questions were genuine, and I am sorry for the unpleasantness that follows whenever I ask a question when Larry is around.
Well said! The subject of twist always draws the most posts and has been discussed forever. Nobody has ever figured out how to call it. Everyone comes up with golden nuggets so it is best to study what everyone says. I don't know if I am right in the way I think about it because so many other things work that should not. Results never agree with one theory.
It is best to form your own ideas based on experience and how it fits with what others say. Much scientific study has been done but until each bullet can be watched for it's whole flight and photographed, all is just based on what the bullet does at the target or at the muzzle. Nobody really knows what is going on in between. What I have been trying to say is that every single bullet/boolit for every single caliber reacts different, let alone gun configurations and barrel lengths and a million other factors.
Just think of what all of you do when you buy a .22 rim fire. You will try every factory round made and maybe some will shoot and others won't. Each has a different velocity, boolit weight or configuration. Then you find one that is super accurate only to find the company has changed the next lot boolit shape to aid production and it now shoots like crap.
There is never a reason to let personal feelings interfere and none of us should argue. It is OK to dispute things without anger!
If all of us were to meet face to face, shoot together, have coffee or a drink, we would all become lifetime friends. Then you will find I am NOT a better shot then most of you, only that I have tweaked my loads and guns to shoot better then I can shoot them. :bigsmyl2:
Except for the Marlin and Browning of course! [smilie=l:

[Larry Gibson]

No point to make here. But, just thinking back on the previous long! thread on this subject I have often wondered about how the sonic/subsonic transition plays into all this. In a previous post on this thread I re-affirmed 44mans observation of bullets that suddenly veer off course. I can't say with certainty the exact range they did it when I watched them go wild but would estimate anywhere between the 150 and 250 yard mark. Given that plus the known that the bullets were leaving the muzzle at about 1250 fps seems possible this flight anomaly was happening about the time the bullets were dropping to subsonic???? Just a thought.


405

This is more than likely the cause. It is well known that many bullets suffer from "inaccuracy" or bullets going "unstable" as they pass back down through the sonic barrier. Many times it is referred to as the "buffeting" of the bullet that causes this. This is no doubt the case with 44man's bullets as you mention (quote above). This "buffeting" is then the precession that causes this effect.

Once again let me caution us not to confuse a bullet that vears off it's travectory as a bullet that becomes "unstable". It is not the same. In the case we are talking about the bullet still has rotational stability but is going off the path of it's intended trajectory because it is influenced by another force. The wind moving the bullet off course is an example of this. The bullet is still rotationally stable and thus it is also when moved off it's trajectory by a precession. Now let me throw a caveat in here. Some precessions are large enough that they can cause bullet a loss of rotational stability; the bullet hitting a small branch for instance. High enough RPM is another. But what we are talking about is not enough of a precession for that.

Larry Gibson

[runfiverun]

that would explain it at the low end but.......
if you are keeping them sonic through the whole distance of say 300 yds, then what is causing it??? deflection? or are the voids in the boolits showing themselves finally..

[Larry Gibson]

I asked a valid series of questions relative to the topic that was being discussed. Questions that I hoped someone had some understanding of that I could benefit from. Your postulated explanation had holes in it. I said so, you took offense and became abusive. As usual.

All;

I've deleted my original post as it is obvious leftiye simply wants nothing more than his usual argument here. I sall not entertain him any further with such.

Larry Gibson

[Larry Gibson]

44man

"Well said! The subject of twist always draws the most posts and has been discussed forever. Nobody has ever figured out how to call it. Everyone comes up with golden nuggets so it is best to study what everyone says. I don't know if I am right in the way I think about it because so many other things work that should not. Results never agree with one theory.
It is best to form your own ideas based on experience and how it fits with what others say. Much scientific study has been done but until each bullet can be watched for it's whole flight and photographed, all is just based on what the bullet does at the target or at the muzzle. Nobody really knows what is going on in between."

44man

I'm not trying to argue with you but let me point out that the science of ballistics is well known. It is science, it is facts and it is not "theory". What happens to your bullets is well understood and proven.

What happens during the bullets (or any projectile) flight is well known. If not then how does artillery or ICBMs hit with such precision miles and thousands of miles away? How is it we put men on the moon when not only the Earth is moving (trajectory) but the Moon is to (it has a trajectory to) How is it we send space craft (projectiles) on trajectories that intercept planets miles away. Or even something simpler and more germane to this discussion; how is it that we know how to make bullets consistently hit a target as small as 10" at 1000 yards (that's the X ring of a high power target)? The answer to these questions is the science of ballistics. We understand and know what happens to bullets in flight. These are not "theories" but facts. These accomplishments along with many, many others could not be done unless we had a complete understanding of ballistics before we fired/launched the projectile. If we only had "nuggets" of opinion which conflict and could only be understood after the fact by "photographing it's whole flight" we could not hit much of anything with a bullet or much of anything else at any distance other than by pure coincidence or luck.

If we are not seeking the factual answer to the question here then being politically nice and accommodating "nuggets" of different "opinions" gets us nowhere and certainly does not provide an answer to the question. Do we seek the answer to the question or is it we just want a consensus of "nuggets"?

Larry Gibson

[Larry Gibson]

that would explain it at the low end but.......
if you are keeping them sonic through the whole distance of say 300 yds, then what is causing it??? deflection? or are the voids in the boolits showing themselves finally..

As the RPM becomes higher in relation to the velocity the increasing centrafugal force then becomes the precession that cauuses the "deflection" even if the bullets are still sonic to the mentioned 300 yards. Keep in mind that the RPM remains the same (for all practical purposes there would be little degradation by "wear off from wind" at that distance) even though the velocity lessens. There are, of course, a few other things that can be "precessions" and cause this effect also; yaw, center of pressure, center of gravity, etc.

Larry Gibson

Let me add; you make the statement, "Nobody has ever figured out how to call it". If some here would bother to do a little study of the science of ballistics they would "know how to call it". Othersise we have the same "discussions" based on "nuggets". The question was a simple one related to twists. The science of ballistics gives us the answer. There are more updated formulas to determine the correct twist. It is the "nugget" of greenhill's Formual that always causes the confusion because as noted it was based on artillery projectiles. It does not work well enough with cast bullets to provide the "best" twist for a particular bullet. There are formulas that do. The answer to your question regarding what happens at 150-250 yards with your revilver bullets is known and has been given.

[Larry Gibson]

44man

"I think precession is predictable, IF that is what causes boolits to go unstable. That is the big question. Now let us say it is the cause. Each boolit will be effected by it at a predictable distance although the direction the boolit decides to go is not. "

Let me suggest you study ballistics. I can give you the title of one book that is easy to read, available and not that expensive if you want. Precession is predictable in that we can say it will happen when the bullet goes subsonic. Exactly when and where the bullet wil move off to is unknown and not predictable as you state.

"The problem is that we are guessing and don't really know. I feel precession is the effect on an over spun boolit at closer ranges until it goes to sleep. The tail might move around while the point stays on track. That fits Larry's definition of touching a top."

It is not "larry's definition". It is the definition in the science of ballistics. It is not "guessing". It is proven fact. What you or I "feel" does not matter. Your "feeling" about presecession is incorrect. What is scientific fact should not be redined here as we "feel".

A boolit DOES lose spin in flight although not as much as a velocity loss. So saying a boolit is spinning at 40,000 rpm's at the muzzle and is still spinning at the same rate at 500 meters is wrong. If a boolit NEEDS 40,000 rpm's to be asleep and drops to 35,000 over distance, it becomes unstable like the slowing top. This is the point outside influence will have the most effect, a gust can start it doing funny things. So is it REALLY precession?

Yes the RPM over 500 yards does degrade a slight amount. It is an amount that is egligible over 500 yards. The math is quite lengthy, if you want to do it I can give you the formuala? I can also give you the formual for bullet stability. You continue to confuse "unstable" with what is happening here. Again, the bullets are no going "unstable". Yes it really is "precession. The precession in your case is caused by the buffeting of the bullets goind subsonic. It is not caused by the bullets "going unstable", the RPM threshold or other things. The reason is very obvious.

"BUT, I might be using the wrong word to start with! [smilie=1: Is precession the point when spin slows and the boolit becomes unstable? I have never found a suitable explanation in any dictionary that refers to anything but the earth in relation to the moon, planets and sun. "

That's the problem with many "nuggets' on this forum. They depend on the position of the Earth, the moon and the stars so to speak. I you stick with the science of ballistics instead of astrollogy you would understand.

To answer your question; NO. Precesion is not, in this case, the point where the spin slows because it has slowed very little. And the bullet is not unstable.
Again, let me state that a precession that movers a bullet off it's intended flight trajectory does not necessarily make the bullet "unstable". You are confused here. Consider wind drifting the bullet; does that make the bullet unstable? no it does not. Simply because a bullet moves off it's intended trajectory does not mean it is "unstable".

"Let's start anew! If precession is the slowing of spin to the point a boolit becomes unstable, that point in distance is predictable for each different boolit but not on paper. It must be found physically. I know of no formula that says at which point spin will decrease enough for a boolit to start to wobble.

Precession is not the "slowing of spin to the point a boolit becomes unstable". You are redefining what precession is and it ain't that. The definition (not Larry's but in the science of ballistics) is; "Precession is is the result of a force being applied to the edge of a spinning object and the following deflection. That's it. In the case of your .44 bullets, somewhere between 150-250 yards they began going subsonic and were buffeted. That "buffet" is the force applied to the edge of the spinning object (the bullet) and the "deflection" was what you observed.

You "feel" the problem is "we are guessing". Sorry, we are not "guessing". This is the science of ballistics. It is fact, it is not a theory. Precession is not the "effect on an over spun bullet" or "the bullet going unstable". Precession, depending on the type, can effect all bullets at all levels of "spin".

"Lets go farther! If a boolit NEEDS 40,000 rpm's, does that change with velocity? I don't think so. I think that boolit needs the same spin at 3000 fps as it does at 700 fps. I don't think foreward velocity has any bearing on spin stability. Eventually we will discover they are two complete different influences, totally separate. Other then the velocity needed to start the spin in the bore."

If the bullet "needs" 40,000 RPM (assuming that is the RPM for the bullet to become stable?) that does not change with velocity. That would be the required RPM for stability regardless of the velocity. The velocity needed for that RPM is dependent on twist. A 10" twist require 555 fps for that RPM. A 12" twist requires 666 fps. A 16" twist requires 888 fps.

So the bullet does need the "same spin at 3000 fps as it does at 700 fps. Understand that if the bullet just attains that 40,000 RPM to become stable at 3000 fps it will not be stable if fired at 1500 fps. Conversely if fired at 3000 fps and stable then when the velocity reduces to 1500 fps the bullet is still stable as the RPM has degraded very little.

"Eventually we will discover they are two complete different influences, totally separate" has already happened. Study the science of ballistics and you will learn that.

"So explain precession! Is it at the start or end of flight? I might be wrong as to where the definition of the word fits! :drinks:
I know where this is going! :mrgreen: I have some goofy ideas! I do a lot of spinning myself."

I have defined "precession" for you and explained how it applies to your .44 bullets in this post and in others. Your idea of what it is is incorrect. Please read the definition and then the original definition (using the gyroscope).

I am partial to good Canadian whiskey!

Larry Gibson

[44man]

Larry, of course I understand all of that and much is known. But how much has dribbled down to cast boolits or to hand loaders? Everyone is still trying to use outdated Greenhill and we have nothing new to use for what we do.
Even taking two boolits that weigh the same and look almost the same, one shoots into one hole and the other is a shotgun.
Almost all scientific studies and results are aimed at military arms with fixed quantities or they can change the quantities to fit.
As hand loaders and casters shooting a million different things, none of us knows what is going on in between the muzzle and target and have no way to find out. We can try to apply all of the scientific theory figured out in how to hit a target at a mile but how does it apply? All we have is trial and error.
Over the years I must have read 10,000 things explaining what twist to use, what load and bullet to use, what each gun needs and guess what? None worked as written. And none of us has the huge number crunching ability of the government.
I don't believe I can box up all of my different boolits, send them to someone and have them tell me exactly what twist, powder, primer, velocity, barrel length, bore size, type of rifling, depth of rifling, case tension, what the boolit does going to subsonic, what it does supersonic, when it will go unstable, how far it is accurate, whether it flies point high or low, whether it will wander from the flight path, how far it will wander, what direction, or a zillion other things that cause a miss.
Anyway you admit that there are no formulas that help us so we are back to square one!
Since gun makers get it wrong all the time the best way for you to prove ballistics are known so well is if I send you my Marlin .44 with the perfect 1 in 38" twist and all of my bullets, boolits so you can shoot me a 5" group at 500 meters with it. I think you will need a 200 foot target, maybe larger! :mrgreen:
You must admit we are talking many different things between us shooters, space and gov't weapons. I just can't find a personal scientist or billion dollar computer to help me.

[leftiye]

As the RPM becomes higher in relation to the velocity the increasing centrafugal force then becomes the precession that cauuses the "deflection" even if the bullets are still sonic to the mentioned 300 yards. Larry Gibson

Increasing centrifugal force? Rpm is constant or reducing therefore centrifugal force is constant or somewhat less. Finding flaws in your ideas isn't just looking for an argument, it is keeping you honest so to speak. What you have alluded to in defining precession would more properly be called deflection maybe? Certainly hitting a branch isn't presession.

[Larry Gibson]

44man

My apologies first of all. I thought I may have peeowed you with those last posts and glad I didn't. I was a little peeowed myself but not at you. Unfortuneately I let it refelect in my tone to you. Glad you let it slide.....sorry.

"Larry, of course I understand all of that and much is known. But how much has dribbled down to cast boolits or to hand loaders? Everyone is still trying to use outdated Greenhill and we have nothing new to use for what we do."

The problem we're face with on this forum is with the "nuggets" based on astrology or opinions based on misconceptions and incomplete knowledge of the facts to be more precise. Many of us here are trying to put all of the "nuggets" in context with ballistic facts. Then we can truely understand what is happening. The problem is there are several who fight that tooth and nail. I'm sure I don't need to further elaborate.

The problem with the Greenhill Formula is twofold; first is, it actually does work. It works well with blunt-nosed jacketed bullets with a specific gravity of 10.9 up through 2000 fps. The constant of 150 in the formula appies to that and a constant of 180 is many times used above 2000 fps. That leads to the second problem, lead has a specific gravity of 11.35 (alloys are different also) and a cast lead bullet, even with lube grooves will be shorter than a similar weight jacketed bullet.

I was asked earlier about this relationship of bullet lengths; cast and jacketed. A 160 gr hacketed 6.5 bullet is the same lenght as a 220 gr 8 mm 323471 cast bullet. A150 RN jacketed bulet is 909" long and a RCBS 30-150-FN w/GC is 868". A 311291 w/GC at 177 gr is .95" compared to a 180 SP at 1.192" The 311299 w/GC is 1.21" with its semi pointed nose compared to a 220 jacked RN of 1.27" and a 220 gr FMJ is 1.31". Those differences may not appear to be much but when factored in to a proper formula for determining twist rate they make a difference indeed!

"Even taking two boolits that weigh the same and look almost the same, one shoots into one hole and the other is a shotgun."

All bullets that look "almost" the same are obviously not the same. If we look closely at the factual difference between the two bullets we will find the correct ballistic reason the one doesn't shoot well.

"Almost all scientific studies and results are aimed at military arms with fixed quantities or they can change the quantities to fit."

I'll assume you meant qualities instead of "quanitiies"? Obviously the government (military's) have more funds for R&D. However many of our own commercial ballistic labs are well aquanted with the scientific facts of ballistics. We must keep in mind that with commercial rifle builders who put the twists in the barrels sold have other interests than what is the "best twist> They focus on production shortcuts that are sufficient not what is "best".

"As hand loaders and casters shooting a million different things, none of us knows what is going on in between the muzzle and target and have no way to find out. We can try to apply all of the scientific theory figured out in how to hit a target at a mile but how does it apply? All we have is trial and error. "

This is the "mental block" here on this forum. We do, in fact, have the knowledge base to know "what is going on in between the muzzle and target". We also could easily "find out" by siply studying and understanding the science of ballistics. Or at least the part that effects the bullet in flight. While it is "rocket science" (couldn't resist the pun) it is not that difficult to understand. We do not have to guess is my point. Once again; ballistics is not "scientific theory", it is scientific fact. The difference betwee theory and fact is that "fact has been proven. Ballistics are proven facts.

"Over the years I must have read 10,000 things explaining what twist to use, what load and bullet to use, what each gun needs and guess what? None worked as written. And none of us has the huge number crunching ability of the government."

10,000 things, eh...whew, that is a lot! Not a lot of "huge number crunching ability" is involved. You obviously have succeeded as you accuracy is very good. There are sound ballistic reasons why your accuracy is better than others. However is 2 moa bad accuracy to some? no it is not. Accuracy is relevent to numerous thins. To use one of your pet peaves; if a Keith .44 bullet shoots 3 moa at 50 yards compared to your WFNs at 2 moa does this mean that the science of ballistics doesn't apply to the Keith bullet? Are all loads that do not match your accuracy level unstable and ballistically unsound? Nope, doesn't mean that at all. It means that there are some very good ballistic reasons your WFNs shoot better for you in your revolvers than do Keith bullets. No wichcraft, astrollogy or old wives tales there, just pure scientific ballistic reasons.

"I don't believe I can box up all of my different boolits, send them to someone and have them tell me exactly what twist, powder, primer, velocity, barrel length, bore size, type of rifling, depth of rifling, case tension, what the boolit does going to subsonic, what it does supersonic, when it will go unstable, how far it is accurate, whether it flies point high or low, whether it will wander from the flight path, how far it will wander, what direction, or a zillion other things that cause a miss.
Anyway you admit that there are no formulas that help us so we are back to square one!"

I never said there were no formulas. We also know there are things that effect accuracy other than a bullets flight. We do not have to go by trial and error as there are formulas which can tell us which twist will be the best for a specific bullet, cast or jacketed. That is certainly not "square one".

"Since gun makers get it wrong all the time the best way for you to prove ballistics are known so well is if I send you my Marlin .44 with the perfect 1 in 38" twist and all of my bullets, boolits so you can shoot me a 5" group at 500 meters with it. I think you will need a 200 foot target, maybe larger!"

Go ahead and send the Marlin and your bullets. I will test those bullets that are appropriate for that 38" twist. I will not waste my time with bullets that are not. I understand ballistic, those that don't waste their time with such. A 5" grooup at 500 meters is only a pipe dream with that rifle. I am not one of several here who espouse such unrealistic expectations.

"You must admit we are talking many different things between us shooters, space and gov't weapons. I just can't find a personal scientist or billion dollar computer to help me."

The help is here on this forum. You just have to listen is all. Reading the book "Understanding Firearm Ballistics" by Robert Rinker is also a good start. There are several other good ballistics books but that is a good one to start with. Saying I just can't find a personal scientist or billion dollar computer to help me" is only an excuse. We both know the max effective range of an excuse is zero meters. There are those of us who do wish to help. Lumping scientific facts in with "nuggets" and then attempting to sort it out puts you at "square one" just about every time.

Might get to the range and test My .41 with the Burris FastFire on it Monday. Looking forward to your advise on how best to use a revolver with an electronic dot sight.

Larry Gibson

[Larry Gibson]

Increasing centrifugal force? Rpm is constant or reducing therefore centrifugal force is constant or somewhat less. Finding flaws in your ideas isn't just looking for an argument, it is keeping you honest so to speak. Isn't precession the tendency of boolits to return to their course due to rotational stability? What you have alluded to would more properly be called deflection maybe? Certainly hitting a branch isn't presession.

The RPM slows very little while the velocity drops a lot. The RPM to velocity ratio then increases dramatically and the centrafugal force becomes the precession. Should you bother to study ballistics you would know that. If you would also read my response to 44man you would find the definition of recession. You would also then know that "deflection" is the end state of precession.

If you had read the books on ballistics and understood ballistics as you claim you would know that hitting a branch is indeed precession.

Your assumptions and questions continue to be argumentative in nature. They also continue to demonstrate your lack of knowledge on this subject. Before you can state someone is wrong, i. e. "keeping you honest", you must know what is the right answer. You do not know the right answer, that is obvious. That is also quite dishonest on your part.

Larry Gibson

[bobk]

Larry,
One quibble: you compare the 291 with a 180 SP. To make things more realistic, the J-should be a 180 RN. Other than that, the bullets and boolits seem to be close in length, although the trend favors the jacketed. However, comparing the 299 with the Hornady RN. the length difference would indicate that the 299 would work with a 1 - 12.6 twist, if a 1 - 12 was correct for the jacketed. That's kinda small.

Bob K

[leftiye]

Larry, You very often chide me for "guessing" or "imagining" Here you're saying that the spin that is correct for a given boolit becomes overspin when the boolit slows down. And that this overspin causes deflection. I am tempted to say "in your dreams." Why then does this phenomenon disappear in long range BPCR and High power when the rate of spin is increased? Do the boolits slow down less or spin slower? Please refrain from playing "The Great Guru of Ballistics" too much Larry.

[Larry Gibson]

bobk

"One quibble: you compare the 291 with a 180 SP. To make things more realistic, the J-should be a 180 RN."

That is a fair quibble. I didn't have a 180 gr RN to measure.

"Other than that, the bullets and boolits seem to be close in length, although the trend favors the jacketed. However, comparing the 299 with the Hornady RN. the length difference would indicate that the 299 would work with a 1 - 12.6 twist, if a 1 - 12 was correct for the jacketed. That's kinda small."

Yes it is a small difference. However it can add up in other ways. My testing ot the .308W with 3 different twists give indications by way of measured BCs as to which twist is 'best" for a given bullet. All 3 twists (10, 12 and 14") stabilized all bullets tested from 125 gr to 180 gr cast and jacketed. Thus we can't say none of them were unstabilized. The higher BCs of the same bullet in the 3 different twists tells us that twist stabilized the bullet better.

We see also that the Greenhill Formual tells us that a 12" twist is sufficient for the 220 gr RN bullet. Many believe the 10" twist is necessary. It would be if theat were a 220 SP.

Larry Gibson

[Lead melter]

44man



Let me suggest you study ballistics. I can give you the title of one book that is easy to read, available and not that expensive if you want. Precession is predictable in that we can say it will happen when the bullet goes subsonic. Exactly when and where the bullet wil move off to is unknown and not predictable as you state.

Larry Gibson

Larry,
Please post or PM the name and point of purchase of the book you mention. Sounds like something I'd like to check out.

Thanks.

[montana_charlie]

Go ahead and send the Marlin and your bullets. I will test those bullets that are appropriate for that 38" twist. I will not waste my time with bullets that are not.
That is one of the most useful things said so far...
CM

[leftiye]

Try round balls!

[Larry Gibson]

Larry,
Please post or PM the name and point of purchase of the book you mention. Sounds like something I'd like to check out.

Thanks.

I was in the Cabela's store a couple weeks ago and they had them. Probably Amazon has them also.

Larry Gibson

[bobk]

Larry,
Has there ever been any work done on measuring RPM degeneration? I envision something with longitudinal bullet marking, a high speed camera, and the bullet breaking a electric screen to trigger the camera. Army Ordinance would have done this, if anyone.

Bob K

[Larry Gibson]

leftiye

"You very often chide me for "guessing" or "imagining" Here you're saying that the spin that is correct for a given boolit becomes overspin when the boolit slows down. And that this overspin causes deflection."

Very quick response so obviously you have neither studied ballistics nor carefully read what I said. I did not say that 44man's bullets were "overspun" and this caused deflection. I said the bullets going back down sub sonic were buffeted and that buffeting was the precession that caused deflection. Please get what I stated correctly.

"I am tempted to say "in your dreams." Why then does this phenomenon disappear in long range BPCR and High power when the rate of spin is increased? Do the boolits slow down less or spin slower?"

Simply because most BPCR shooters shoot loads that are subsonic to begin with or they go sub sonic very close to the muzzle. Thus there is no precession to cause this type of deflection. Note that bullets going sub sonic is a bane to high power shooters shooting at 1000 yards. It happens to them when the 168 MK is fired out of .308Ws with 10 11" twists at muzzle velocities of 2600 fps or less. Same thing happens to them there that is happening to 44man.

"Please refrain from playing "The Great Guru of Ballistics" too much Larry."

Very cute, and so much like you leftiye. You can't engage in a discussion with facts so you start with the personal attacks and SA comments. Keep in mind that argumentative questions, even though questions, are still argumentative.

Could we ask, since you continue to say we are wrong, where is your right answer to this question?

Larry Gibson

[Larry Gibson]

Larry,
Has there ever been any work done on measuring RPM degeneration? I envision something with longitudinal bullet marking, a high speed camera, and the bullet breaking a electric screen to trigger the camera. Army Ordinance would have done this, if anyone.

Bob K

Yes, there has been. You are correct that it was the military ordnance types.

There is a formula to compute it but it is quite involved. Would you like to do the math? Quite frankly, I don't. The ordance/ballistics types have done it enough that, suffice to say I take it as fact that the RPM slows very little, an insignificant amount actually, over the course of a bullets flight even when fired at maximum ordnace.

Larry Gibson

[leftiye]

leftiye

"You very often chide me for "guessing" or "imagining" Here you're saying that the spin that is correct for a given boolit becomes overspin when the boolit slows down. And that this overspin causes deflection."

Very quick response so obviously you have neither studied ballistics nor carefully read what I said. I did not say that 44man's bullets were "overspun" and this caused deflection. I said the bullets going back down sub sonic were buffeted and that buffeting was the precession that caused deflection. Please get what I stated correctly.

I responded quickly so I don't know anything about ballistics? That's ripe. What's 44Man got to do with it? You've consistently pursued this thing about the relationship between rpm being the same while velocity drops as causing instability. If that's the case why do they increase twist to increase accuracy over the slower twist guns that exhibit the inaccuracy? It's not about going subsonic either - look at the 71/2 " twists in the .223s used in High Power.


"I am tempted to say "in your dreams." Why then does this phenomenon disappear in long range BPCR and High power when the rate of spin is increased? Do the boolits slow down less or spin slower?"

Simply because most BPCR shooters shoot loads that are subsonic to begin with or they go sub sonic very close to the muzzle. Thus there is no precession to cause this type of deflection. Note that bullets going sub sonic is a bane to high power shooters shooting at 1000 yards. It happens to them when the 168 MK is fired out of .308Ws with 10 11" twists at muzzle velocities of 2600 fps or less. Same thing happens to them there that is happening to 44man.

One way or the other Larry, not both. Either it is about sonic to subsonic transition, or it is not. In either case, why do MORE rpms solve the problems that TOO MUCH RPMS caused in the first place (according to yourself)?


Please refrain from playing "The Great Guru of Ballistics" too much Larry."

Very cute, and so much like you leftiye. You can't engage in a discussion with facts so you start with the personal attacks and SA comments. Keep in mind that argumentative questions, even though questions, are still argumentative.

So you say. Isn't THAT a personal attack??? Quit trying to manipulate the rules of discussion and try following them instead. Labeling things you don't like as " argumentative" is baloney. BTW argumentation is a standard term in philosophy, and NOT a bad thing even if you say so. When is it not argumentative? When I agree with you? As I said, If you don't like my questions, don't answer them.

[Larry Gibson]

leftiye

"I responded quickly so I don't know anything about ballistics? That's ripe. What's 44Man got to do with it? You've consistently pursued this thing about the relationship between rpm being the same while velocity drops as causing instability."

Quite untrue. I'm sure all reading here know how many times I've corrected 44man and others that we are not talking about unstable bullets. We are talking about about the movement of the bullet away from it's intended flight path. Instability is not the reason. Comprende"?

"One way or the other Larry, not both. Either it is about sonic to subsonic transition, or it is not. In either case, why do MORE rpms solve the problems that TOO MUCH RPMS caused in the first place (according to yourself)?"

Obviously you are now very, very confused. There is a transitional period from sonic to subsonic. It is not finite as in; 1078 fps is sonic and 1077 fps is subsonic. I have no idea where you came up with the concept in the second sentence. You now appear to be arguing with yourself, and losing at that.

"Isn't THAT a personal attack???"

Yes it is. Everyone here knows how you meant it.

"Could we ask, since you continue to say we are wrong, where is your right answer to this question "

You quoted the above but failed to answer, please do. I am not going to respond any further to your argumentative questions unless you answer the above. You can not say we are wrong unless you can say what is right. Please enlighten us and quote your sources please.

Larry Gibson

[felix]

Also, what is interesting is that it can take as much as 33 percent of the total energy provided by the powder to make the projectile rotate to spec. Naturally, that is dependent on the projectile parameters and twist parameters together. As a side note, it is extremely difficult to apply any kind of discrete mathematics to the physical phenomenon being discussed in this whole thread. There are many such formulas in and about the guts of the problem dealing with all kinds of flight, and none of them are correct enough for some applications. That's why guided projectiles exist....to get around some of the ballistic problems not being emulated exact enough in advance of firing. ... felix

[Lead melter]

I was in the Cabela's store a couple weeks ago and they had them. Probably Amazon has them also.

Larry Gibson


Maybe I missed something, which would not be hard to do considering the amount of information, conjecture and opinion that has been brought forth in this thread, but I didn't see the name of the book.

If I missed it, please excuse my mistake.

[leftiye]

The bullets at longer range when velocity drops become over stabilised and other things, such as precession, begin to radically effect stabilitity. Larry gibson

Quote:
As the RPM becomes higher in relation to the velocity the increasing centrafugal force then becomes the precession that causes the "deflection" even if the bullets are still sonic to the mentioned 300 yards. Larry Gibson

As prevoiusly stated if rpms remain constant or decrease, then centrifugal force remains constant or decreases.


Quote:
You've consistently pursued this thing about the relationship between rpm being the same while velocity drops as causing instability Leftiye

Quote:
Quite untrue. I'm sure all reading here know how many times I've corrected 44man and others that we are not talking about unstable bullets. We are talking about about the movement of the bullet away from it's intended flight path. Instability is not the reason. Comprende"? Larry Gibson

Oh yes, we WERE talking about instability. What else can you call it when a boolit departs its flight path without outside influence? When I asked the question in the first place I asked about and used the term "instability." In your earlier responses you yourself used the term instability. Now you try to cloud the issues with what amounts to a semantic ploy.

The question still remains - how is it that this problem (call it what you will) that is caused by too many rpms is cured by going to a tighter twist?


Quote:
"One way or the other Larry, not both. Either it is about sonic to subsonic transition, or it is not. In either case, why do MORE rpms solve the problems that TOO MUCH RPMS caused in the first place (according to yourself)?" Leftiye

Quote:
"Obviously you are now very, very confused. There is a transitional period from sonic to subsonic. It is not finite as in; 1078 fps is sonic and 1077 fps is subsonic. I have no idea where you came up with the concept in the second sentence. You now appear to be arguing with yourself, and losing at that. " Larry Gibson

Doesn't the second sentence of my quote above say "sonic to subsonic transition"? As to where it comes from, SEE YOUR POSTS ABOVE. The other concept you allude to also comes straight out of your earlier comments above. Thems the facts Larry.


Quote:
Very cute, and so much like you leftiye. You can't engage in a discussion with facts so you start with the personal attacks and SA comments. Keep in mind that argumentative questions, even though questions, are still argumentative. Larry Gibson

So you say. Isn't THAT a personal attack???" Leftiye

(And Now Larry's version):


Quote:
"Isn't THAT a personal attack???" Leftiye

Yes it is. Everyone here knows how you meant it. Larry Gibson

I was alluding to your personal attack, and likewise, everyone knows just how you meant it. Do you not seem to be a little confused?

Yes Larry,
The posts are right next to one another. I'll leave it to everyone to simply compare and see who is distorting what. "we?, us?" - you've got a mouse in yer pocket?

[45 2.1]

You can always tell where Larry is or has been (most recently on the Accurate forum where he got very snooty with several folks). At that spot is a great controversy because the people don't believe what he says and he writes long posts berating them because they don't see his self-imminent brilliance. Give it a rest Larry, most everybody is bored with your theory.

[leftiye]

For what it is worth - At one time (beginning with post #33) in this thread there was much discussion of the fact that at longer distances best accuracy required a tighter twist than best accuracy required at shorter distances. My original question was why this would be the case if rpms hadn't abated to any material degree. One would expect that virtually the same rpms that sucessfully stabilized the bullet when it was traveling faster earlier in it's flight would continue to have ample stabilizing power at any distance (and it does). Larry offered his theory that the relative rpms became too high as velocity decreased (see my last post). I asked him how it could be the case that the relatively higher revolutions vis a vis velocity at the longer distances caused precession when even more rpms from a tighter twist barrel added to the very same loads solved the problem. I've asked him this question many times here now and he hasn't addressed it yet. To be honest, I don't think he nor anyone else can answer that one. It presents an apparent contradiction. The answer is that his theory doesn't work.

[leftiye]

Could it be that the extra rpms from the tighter twist add more stability to resist buffeting, and thereby stop precession (better known in this case as inaccuracy)? Or is that too easy? Could it be that as the boolit slows it becomes more vulnerable to deflection (less momentum ya know)? There you have the answer you were asking me for Larry. Pick it apart if you can. If you do, I'll take the easy way out and admit that I was wrrrrrr.... (unlike someone we know).

[Larry Gibson]

Maybe I missed something, which would not be hard to do considering the amount of information, conjecture and opinion that has been brought forth in this thread, but I didn't see the name of the book.

If I missed it, please excuse my mistake.

Lead Melter

Sorry, I did mention it a couple times but I should have included it, my fault.

"Understanding Firearm Ballistics"

By Robert A. Rinker
Mulberry House Publishing
Clarksville, Indianna

Larry Gibson

[Larry Gibson]

Also, what is interesting is that it can take as much as 33 percent of the total energy provided by the powder to make the projectile rotate to spec. Naturally, that is dependent on the projectile parameters and twist parameters together. As a side note, it is extremely difficult to apply any kind of discrete mathematics to the physical phenomenon being discussed in this whole thread. There are many such formulas in and about the guts of the problem dealing with all kinds of flight, and none of them are correct enough for some applications. That's why guided projectiles exist....to get around some of the ballistic problems not being emulated exact enough in advance of firing. ... felix

Exactly felix, such is why the moment of precession is not prdictable and also why the moment of sub sonic transition. We know these things happen, we know why they happen, but to predict (calculate) the exact moment of happening is almost impossible because of the myrid things that happen (variables) and when the also happen andwhat the effects those variables have.

We can predict that precession is going to happen to a bullet when it goes subsonic. The exact foot from the muzzle is variable. We can predict the bullet will lose accuracy. The exact amount is variable. We can predict a certain bullet will lose more accuracy than another but the amount is variable. That is what is meant.

Larry Gibson

[bobk]

Larry,
What you are implying about the math makes my head hurt. What I was looking for, though, was empirical data, or a way to obtain it. Formulas are fine, as long as they correspond to reality, but for that to happen reliably, the calculations should be derived from observation, rather than assumption.

Bob K

[Larry Gibson]

leftiye

You quote out of context, very common to you.

"Oh yes, we WERE talking about instability. What else can you call it when a boolit departs its flight path without outside influence? When I asked the question in the first place I asked about and used the term "instability." In your earlier responses you yourself used the term instability. Now you try to cloud the issues with what amounts to a semantic ploy."

The precession is the "outside" influence. The precession does not have to be "outside" but may also be inside such as the centrafugal force. Where in the definition of "precession" does it say "outside influence"? It does not, this is just another figment of your imagination. It is also a further example of your lack of knowledge and understanding of ballistics. Your continued insistance that a bullet must be unstable to move off it's intended path of flight is also incorrect. Go study ballistc then come back with some intelligent questions. Again, you state we are wrong yet do not or can not provide what is right. Really bad form you know.

Have the answer to this question or will you just proceed with more argumentative questions? Obviously you do not have the answer. You will continue with questions and state nothing yourself. Commit yourself since you are continually correcting us and answer the question of this thread yourself.

Larry Gibson

[Larry Gibson]

You can always tell where Larry is or has been (most recently on the Accurate forum where he got very snooty with several folks). At that spot is a great controversy because the people don't believe what he says and he writes long posts berating them because they don't see his self-imminent brilliance. Give it a rest Larry, most everybody is bored with your theory.

I notice you're still here reading it. And Joe is still here reading it so he can post on the Accurate Forum. Aside from leftiyes persistant argumentative questions there has been some good information put out here. Perhaps you have something of substance to add?

Larry Gibson

[Larry Gibson]

Could it be that the extra rpms from the tighter twist add more stability to resist buffeting, and thereby stop precession (better known in this case as inaccuracy)? Or is that too easy? Could it be that as the boolit slows it becomes more vulnerable to deflection (less momentum ya know)? There you have the answer you were asking me for Larry. Pick it apart if you can. If you do, I'll take the easy way out and admit that I was wrrrrrr.... (unlike someone we know).

leftiye

Asking questions is not an answer. An answer makes a difinative statement back up by facts of what is. You do not commit to anything definitive by asking further questions that way and it leaves you a "back door way out" you apparently desire.

Make a statement of what the answer is to lead melter's or 44man's question.

Larry Gibson

[Larry Gibson]

Lead melter

My apolofies for allowing leftiye to distract this thread with his arguements. His arguments are always simply aimed at me regardless of the subject. I could probably agree 100% with him and 45 2.1 and they would still want to argue about it.

If you can't find find that book let me know and I'll run down to Cabella's and see if they've a copy there still. Rinker writes in a style that makes it about 98% comprehensible for us laymen. He is about 98% in agreement with most other books (or the parts of them that deal with firearms ballistics). He goes into detail on many things but skips over other topics. I was dissapoited with his lack of material regarding cast bullets as a seperate discussion. But since he touches on numerous firearms topics that are actually not ballisitacally related the book is fairly comprehensive. The book is a good start to understanding the science of ballistics and applying that knowledge to cast bullets.

Let me know if I can help you find the book. If you are anyone else (other than leftiye and 45 2.1) have pertinant comments or questions regarding this topic I will be glad to further comment if I have the answers. If I don't then perhaps together we can find the answers.

Larry Gibson

[45 2.1]

I notice you're still here reading it. And Joe is still here reading it so he can post on the Accurate Forum. Aside from leftiyes persistant argumentative questions there has been some good information put out here. Perhaps you have something of substance to add?
Larry Gibson[/quote]

I have, many times, and have taught others to achieve the same. You, on the other hand , have steadfastly refused to learn how to achieve real accuracy with high velocity. Real accuracy is not 2 or 3 MOA at 2400 fps as you have stated. Real accuracy is comparable to that achieved with those full length gas check bullets. Some of the current forum members are now doing it with paper patched boolits. Why don't you try a mold that actually fits instead of that poor excuse for a mold you have now and claim is a normal cast boolit. Poor thing was cut with a many times sharpened cherry that should have been tossed the sharpening before. Thats your test, get a 311291 that actually casts 0.311" on the bands and has at least a 0.301" nose (instead of that sub 0.299" nose). That should change the results of your tests greatly, provided you learn how to use the proper alloy and powder for the pressure level used. I suspect you'll go on with this test and results though and berate people (lots of examples out there of that) for not agreeing with you like before.

[montana_charlie]

I just read something that made me look at the 'stability' thing from a different angle.
A guy was shooting a 38-55 bullet that 'seemed too heavy' for his 18-inch twist...so he shortened his mould. No results to report at this time...

I was surprised to hear he had that twist in a 38-55, so I looked at the Cimmaron site to check on the Uberti specs. Sure enough, they use that rifling for that cartridge...while 14" is preferred by some others.

So, I got to thinking...kinda like leftiye does.
We all (probably) will agree that a slow rifling handles short bullets, and vice versa.

It's a known fact that 1 in 18 works well for the .45's shooting long heavy bullets to acheive long range capability. Let's say those bullets are 1.4 inches (that is not exact, but let's say so, anyway). That length is about three times the caliber...or a 3:1 length/width ratio.

I'll assume that a cylindrical object of a given ratio will fly true as long as it's RPM is sufficient. That RPM is established while within the barrel, and is maintained throughout the flight.
Changing the shape of the object will affect aerodynamic efficiency (ballistic coefficient) and can change the 'balance' of the bullet so that it can be upset easily...or not so easily...by outside influences.

But, disregarding the differences caused by 'shape', would it be reasonable to assume that an 18" rifling would always(?) be a good choice if the bullet used (regardless of caliber) maintains that 3:1 length/width ratio?

CM

[Larry Gibson]

Sorry folks

I deleted my original response to 45 2.1s post above.

It is not worth the effort or the distraction responding to 45 2.1 when he also continues to just argue. Should he come up with something pertinant to this thread and Lead Melter's or 44man's questions then I shall respond. This thread is not about the RPM threshold.

Larry Gibson

[Larry Gibson]

montana_charlie

"But, disregarding the differences caused by 'shape', would it be reasonable to assume that an 18" rifling would always(?) be a good choice if the bullet used (regardless of caliber) maintains that 3:1 length/width ratio?"

That is pretty close to the gist of it. Any bullet of that caliber, regardless of shape/weight, that fits that ratio will be properly stabilized (under the parameter assumptions you made).

However, let us consider the differences caused by "shape". We know that altering the shape from the blunt RN bullet to a spitzer pointed bullet with a boat tail while maintaining that ratio makes for a much lighter bullet. The lighter bullet would probably be better served in a slower twist for best stabilization. In the 18" twist the lighter bullet will also achieve stabilization at a lower velocity/RPM than that of the heavier RN bullet. The lighter more streamlined bullets are then more stabilized in the 18" twist.

On the other hand, if we maintain the same weight of the bullet and stream line it then the bullet will be longer, the ratio will change and a faster twist may be required for proper stabilization at equal velocity. Or we have to push it faster to achieve a higher RPM for stabilization in the 18" twist.

Larry Gibson

[45 2.1]

Had you been reading and paying attention you would know that I achieve sub 2 moa accuracy at 2600+ fps with 311466 in the 14" twist. You got a link to that? Do you? Yes, with a faster twist. You might also know that both Bass and I acheived that level of accuracy with 31291 at 2300+ fps. Have you? Well yes, I have, but why stop there. Larry, your efforts at high velocity accuracy are lacking. Even with a 311291 that "fit"? Now as to your test. Sorry, but if you would read you also know i already have ran that test with a 311291 (GB) that casts out .314 on the driving bands and .302-3" on the nose. Guess what? Results are the same as with the Lyman 311291. Part of the test you didn't post? That GB bullet got taken to the cleaners by the RPM threshold just like the lyman bullet. Now like any good witch doctor with a majic potion you have thrown the caveats in there. Larry, i'm just holding you to the same requirements you want out of others. Why call someone names, is your command of the language that limited? So I guess every one here will really believe I can't "use the proper alloy and powder for the pressure level used." Ahhh, now you have it. Had you used the proper alloy and powder, you would be able to match what BaBore, 357 Maximum and I have done, not to mention Starmetal Joe. But you haven't.

[onceabull]

"real accuracy is comparable to that achieved by those full length gas checked bullets.some of the current members are now doing it with paper patched bullets.." Any year now we will see some of these guys in the long range matches at Camp Perry showing the Gallagher,Tompkins,and Tubb families and the rest of the world how to do it, NOT.. But step up and be first to try....!! Oh,sorry, I forget, those matches are mostly about reading the wind,Eh..

[onceabull]

Starmetal Joe can't be included..He has the unfair advantage of bullets that roll over faster after they leave the barrel,and "special "friends "at Sierra ballistics....:groner: Onceabull

[Larry Gibson]

Sorry folks

I rest my case regards 45 2.1.

I deleted that post so as to not let him go into all that. Unfortuneately he grabbed it and is running with it.

Larry Gibson

Added; it is unfortunate but it appears 45 2.1 dislikes me to the extent that he goes off ruining every thread until they are closed down. I'll just continue to ignore. Maybe we can continue here with some semblence of an intelligent discussion of this matter in spite of him. Again, my apologies for his posts.

[45 2.1]

Always good to see your posting Bill [onceabull, idabull on Accurate]. Same thing you always put out. :mrgreen:

It is not worth the effort or the distraction responding to 45 2.1 when he also continues to just argue. Larry, its not argueing. I, and others, just don't agree with what your saying.Should he come up with something pertinant to this thread and Lead Melter's or 44man's questions then I shall respond. I don't believe its your thread nor its moderatorThis thread is not about the RPM threshold. Somehow, I think your going to slip that in.

[onceabull]

And your stuff is always fresh new material,eh, Bob?????? :roll: Onceabull

[felix]

CM. the twist requirement must take into account the square of the boolit's radius when changing groove sizes. The 1 to 3 ratio within a single diameter would work fairly well as Larry said.

[44man]

I have been hand loading and working loads for accuracy for over 55 years. In every case with any gun, if the proper bullet was chosen, groups slowly tightened with an addition to the load until the best accuracy was found, then any additional increases resulted in groups opening again. Sometimes a powder change made tighter groups but the results still came the same way. Never, ever did pushing the envelope result in smaller groups.
All of my cast boolit shooting has worked the same way. Work up and never find accuracy over what the boolit needs so I just back down to the right load.
I have never been able to say that a boolit reached any kind of a threshold because to continue raising the velocity always resulted in poor accuracy. If a boolit shoots best at 2100 fps, taking it to 3200 fps is not going to tell me that it came apart or not, just that it is way too fast and spins too much and is a mismatch to the twist at the high speeds.
Sorry but I never found any bullet that will shoot 1" groups from 700 to 3500 fps! All only shoot at a very tight band near the best velocity and even an outside temperature change, humidity change, a change in elevation, even a change in lot numbers will blow groups. Even the time of day and sun position effects it.
I will continue to rely on working loads and experience when I load and stay away from books and theory.
The military has hundreds of years experience and billions of our tax dollars to make things shoot.
A puff of smoke in front of the gun from a boolit blowing up only tells me I am WAY, WAY past the point where the boolit shot good groups. Why even persue it?

[Pat I.]

Larry sometimes I don't know why you bother . You'll never be able to have a decent conversation once the 2nd best shooting keyboard on the net gets involved. Some agree with you some don't, in the grand scheme of things who cares??

To answer the original post. With lead bullets stick with Greenhill no matter what anyone tells you and you won't go wrong

[leftiye]

Originally Posted by leftiye
Could it be that the extra rpms from the tighter twist add more stability to resist buffeting, and thereby stop precession (better known in this case as inaccuracy)? Or is that too easy? Could it be that as the boolit slows it becomes more vulnerable to deflection (less momentum ya know)? There you have the answer you were asking me for Larry. Pick it apart if you can. If you do, I'll take the easy way out and admit that I was wrrrrrr.... (unlike someone we know).

leftiye

Asking questions is not an answer. An answer makes a difinative statement back up by facts of what is. You do not commit to anything definitive by asking further questions that way and it leaves you a "back door way out" you apparently desire.

Make a statement of what the answer is to lead melter's or 44man's question.

Larry Gibson

Dern, Larry, what a BOS. It was the furthest thing in my mind to dodge anything there. Sounds more like you're the one doing the dodging. Do you like the idea or don't you? What's the diff if I posed my answer as a suggestion (in question marks) - I still postulated the answer you asked for.

I still don't see any response to the question that was first asked. Nor do I see any response to the charge that your idea $u#k$. Who is it that's not dealing in facts here? How about a little "I was wrrr..." from you?

[montana_charlie]

montana_charlie

"But, disregarding the differences caused by 'shape', would it be reasonable to assume that an 18" rifling would always(?) be a good choice if the bullet used (regardless of caliber) maintains that 3:1 length/width ratio?"

[B]That is pretty close to the gist of it. Any bullet of that caliber, regardless of shape/weight, that fits that ratio will be properly stabilized (under the parameter assumptions you made).
Uhh...that wasn't quite what I was getting at. I wasn't staying within one caliber...I was wondering of the ratio should work well, regardless of caliber.

Take the 1.4-inch long .45. 1.4 divided by .458 gives you (close to) 3.

Then, a 38-55 bullet is (say) .379" 'fat' and (perhaps) 1.13" long. Since it conforms to the '3:1 rule', an 18 twist should make it go.

But, if the .38 caliber bullet were 1.4 inches long...the ratio would be 3.7:1.
It would be nice if you could say a bullet with a 3.7:1 length/width ratio needs a (say) 14 twist.

See where I'm going?

I'm in the middle of getting a roast ready for dinner, so I haven't taken time to research 'standard' bullet dimensions, or popular twist rates, in various calibers...
CM

[Pat I.]

Maybe like getting the 6.5 Swede to shoot at 2400 fps this is one of those "Graduate Level" things that can't be taught on the internet. :grin:

[Larry Gibson]

Leftiye

"How about a little "I was wrrr..." from you?"

Seems that is what everyone is waiting to hear from you.

I will answer your question but will you answer mine? We all know you will not.

"Could it be that the extra rpms from the tighter twist add more stability to resist buffeting, and thereby stop precession (better known in this case as inaccuracy)?"

If the bullet is marginally stabilised the answer is yes. It is known that bullets are about 1 1/2 times more stable around 500 yards that at the muzzle (if they have not dropped back down the sonic barrier). Thus if we have a bullet that is marginally stable at the muzzle it becomes more stable as velocity drops and rpm stays the same. If that bullet is at the "fully stabilized stage (there are 3 basic stages of bullet stability; marginal, fully and over stabilized) when it begins transition to subsonic it is more able to resist the buffeting. However if a bullet is at maximum stability at the muzzle it then becomes over stabilized as velocity drops and the RPM stays the same. That bullet is then more suseptable to the buffeting as the precession will have a greater effect because of the higher RPM. This is why a 174/175 gr match bullet has a higher BC and will stay transonic longer with better accuracy when fired out of 12" vs a 10" twist at the same velocity.

As to your second question I'm not sure what you mean by "vulnerable to deflection". Explain further and I'll answer if I understand what you are say. Now don't go off and say I'm avoiding the question here. I am not...I do not undestand your meaning or point.

Now will you answer my question; if what I say is wrong regarding Lead Melter's and 44man's question, then what is the right answer?

Larry Gibson

[Larry Gibson]

Larry sometimes I don't know why you bother . You'll never be able to have a decent conversation once the 2nd best shooting keyboard on the net gets involved. Some agree with you some don't, in the grand scheme of things who cares??

To answer the original post. With lead bullets stick with Greenhill no matter what anyone tells you and you won't go wrong

Pat I

I don't know why I bother either. I tried to give the answer to Lead Melters and 44man's questions. Leftiye and 45 2.1 come in an want to turn it back into the RPM threshold type argument again. I think they obvious dislike of me totally clouds their minds. They fail to take anything I say as fact and assume it is all some part of the RPM threshold. The results are, instead of learning anythin 44man is throwing in the towel with; "I will continue to rely on working loads and experience when I load and stay away from books and theory". Leftiye and 45 2.1 have him believing that ballistic facts are "theory". Too bad.

Larry Gibson

[Larry Gibson]

Uhh...that wasn't quite what I was getting at. I wasn't staying within one caliber...I was wondering of the ratio should work well, regardless of caliber.

Take the 1.4-inch long .45. 1.4 divided by .458 gives you (close to) 3.

Then, a 38-55 bullet is (say) .379" 'fat' and (perhaps) 1.13" long. Since it conforms to the '3:1 rule', an 18 twist should make it go.

But, if the .38 caliber bullet were 1.4 inches long...the ratio would be 3.7:1.
It would be nice if you could say a bullet with a 3.7:1 length/width ratio needs a (say) 14 twist.

See where I'm going?

I'm in the middle of getting a roast ready for dinner, so I haven't taken time to research 'standard' bullet dimensions, or popular twist rates, in various calibers...
CM

CM

I now see where you were going. That is interesting, I had not thought of that before. It could very well be, just have to do the math and see how it pans out and correlates to known facts. Are you going to do the math?

Let me know how dinner turns out:-)

Larry Gibson

[montana_charlie]

Are you going to do the math?
Nope...I'm gonna peel potatoes...put 'em in with the roast...and clean the kitchen.
CM

[onceabull]

Pat I: If Larry G. didn't enjoy throwing bait out on the water he would probably leave a thread like this the first time he's annoyed.. As is, he's usually good for a couple of dozen more posts if the "anti's" keep on posting.. Last man standing wins.....WHAT ??...Once Larry finds something more interesting to do, the "anti's" can go back to patting themselves on the back.... :brokenimaOnceabull

[leftiye]

"Now will you answer my question; if what I say is wrong regarding Lead Melter's and 44man's question, then what is the right answer?" Larry Gibson

Give me a clue as to what that all might be please? I thought that was what I just answered.

[leftiye]

Ounceabull,
I think you're right. Larry must be baiting us. After all he won't answer any questions except after several pages of mouthwash. (just what it takes to get an immediate and straight answer, no one knows) But what keeps him going is his ego.

[44man]

No, I have not given up! :Fire: Only that I have never read anything in any book that has made my guns shoot better. Almost all has been tried and long ago pitched in the scrap heap.
It is like reading the "Duke", yeah the guy that thinks he is John Wayne, pushing SPG lube. Absolute crap that fills the bore with hard, dry fouling.
From all I read here the 6.5 Swede should not shoot past 25 yd's. All 1 in 10" .30 cal rifles are wrong. The .22-250 should out shoot the .220 Swift because the twist is slower. The fabulous .244 was a bad cartridge because the twist was wrong and the *** .243 won out with the faster twist. I could go on for hours but still come up with the same conclusions, ALL rifles with slow twists have gone by the wayside.
Back to revolvers! [smilie=1: No one has ever posted better long range groups on any site that even come close to what my fast twist BFR's shoot. 25 yd groups with other guns from a ransom rest can't touch them. It is so funny, I have been accused of lying!
You can talk for the next 365 days trying to convince me my guns should have slower twists, I will laugh all the way to my targets! :mrgreen:

[Pat I.]

I think the slower twists have gone by the wayside not because they were wrong but because manufacturers have to build a one size fits all rifle to satisfy the masses. If you check Savages website they put 12 or 13 twist barrels on their target 308 rifles and and 10 on their other 308 offerings.

[onceabull]

I'd laugh all the way to my targets ,too, if I could shoot a .07 MOA group @ 350 yds.. even once, because I'm sure I would go on to win the big $, have Nascar like sponsorship offers,and be able to afford all the shooting components I would ever need..[smilie=1: :roll: Onceabull

[44man]

I'd laugh all the way to my targets ,too, if I could shoot a .07 MOA group @ 350 yds.. even once, because I'm sure I would go on to win the big $, have Nascar like sponsorship offers,and be able to afford all the shooting components I would ever need..[smilie=1: :roll: Onceabull
Hate to break your bubble but it was a .250" group. That rifle head shot chucks to beyond 600 yd's. Darn, it had the wrong twist too! [smilie=1:
Pat, that is true, the specific target rifle is designed for one bullet, not what all of us hunters use. It is designed for one range where bullet rotation around the flight path is gone. It has nothing to do with what the average shooter does, hence a faster twist to cover all bases.
Just like the .44 Marlin, it probably needs the 180 gr bullet or a round ball. I bought it to hunt with using heavy boolits. It is, like a specific target rifle, an abortion not suited for the masses.

[Pat I.]

True but that doesn't mean that the twist isn't better suited for accuracy. Just because some guy thinks he needs a 220 gr 30 cal bullet to kill a deer doesn't mean that a 10 twist is the best thing to use in a 30 cal., it's just what the manufacturers have to use to keep the hounds at bay.

[45 2.1]

No, I have not given up! :Fire: Only that I have never read anything in any book that has made my guns shoot better. Almost all has been tried and long ago pitched in the scrap heap.
It is like reading the "Duke", yeah the guy that thinks he is John Wayne, pushing SPG lube. Absolute crap that fills the bore with hard, dry fouling.
From all I read here the 6.5 Swede should not shoot past 25 yd's. All 1 in 10" .30 cal rifles are wrong. The .22-250 should out shoot the .220 Swift because the twist is slower. The fabulous .244 was a bad cartridge because the twist was wrong and the *** .243 won out with the faster twist. I could go on for hours but still come up with the same conclusions, ALL rifles with slow twists have gone by the wayside.
Back to revolvers! [smilie=1: No one has ever posted better long range groups on any site that even come close to what my fast twist BFR's shoot. 25 yd groups with other guns from a ransom rest can't touch them. It is so funny, I have been accused of lying!
You can talk for the next 365 days trying to convince me my guns should have slower twists, I will laugh all the way to my targets! :mrgreen:

Best post of the entire thread....... For all the book readers here, those books only contain a little truth, just enough so you really have to know what your doing to glean which part is the truth and which part is BS. Nothing beats trying it yourself. As for posting unbelievable groups and deeds, Elmer did that and was called a liar for years, but was vindicated by a lot of folks that repeated his achievements long after he did them. Jim and I just got called liars and keyboard shooters. Someday some bright guy will do the same, unlike the current crop of rather dim bulbs that crawl out from under their rock and likewise post here.

[Pat I.]

So let me get this straight since I have a fairly good selection of gun related reading material that I enjoy browsing through. If I read it in a book it's all half truths and lies but if I read it here it can be taken as gospel. So what you book banners are saying is that it's not the words but the medium by which they're delivered, that is until you can find something in a "book" to back up one of your argument.

Can't speak for anyone else but personally I don't find the term "book reader" to be offensive while on the other hand being considered a keyboard shooter or BS artist, well............

[45 2.1]

So let me get this straight since I have a fairly good selection of gun related reading material that I enjoy browsing through. If I read it in a book it's all half truths and lies but if I read it here it can be taken as gospel. So what you book banners are saying is that it's not the words but the medium by which they're delivered, that is until you can find something in a "book" to back up one of your argument. Really Odd take on what was said, but i'll consider the source this time.

Can't speak for anyone else but personally I don't find the term "book reader" to be offensive while on the other hand being considered a keyboard shooter or BS artist, well.... You evidently didn't grasp the bulb concept......... As for the 6.5 Swede, everything you need to know is on the site here, whether you understand it or not is another thing entirely.

[Pat I.]

You evidently didn't grasp the bulb concept......... As for the 6.5 Swede, everything you need to know is on the site here, whether you understand it or not is another thing entirely.

I understand it completely now, it's the old NIH syndrome.

[45 2.1]

I understand it completely now, it's the old NIH syndrome.

Nope, its really old material and has been in print for a long time. I didn't invent it at all. One of those things you can read about, but don't know which is right and which is BS. The main problem is whether you understand what you read, evidently you haven't.

[Pat I.]

Guess I'll have to get me one of those 1/4 inch shooting 450 Marlins like you have so I can really start to understand everything. :coffee:

[44man]

So let me get this straight since I have a fairly good selection of gun related reading material that I enjoy browsing through. If I read it in a book it's all half truths and lies but if I read it here it can be taken as gospel. So what you book banners are saying is that it's not the words but the medium by which they're delivered, that is until you can find something in a "book" to back up one of your argument.

Can't speak for anyone else but personally I don't find the term "book reader" to be offensive while on the other hand being considered a keyboard shooter or BS artist, well............
No, you should not believe anything you read no matter where you read it. I have done nothing to force you to believe a word I said because they are my thoughts, just like all the stuff in magazines.
You must do like I have done, go out and do it and form you own opinions.
Lots of science and math books out there but none tell you how to apply the information to your boolit or gun, they just say it "should" work. I am not going to be the one to tell you to get off your chair either! :mrgreen::mrgreen::mrgreen:
All I see in the gun rags anymore are a bunch of rich guys showing off huge collections. The others are stuffed with carry crap, military weapons and $5000 hunting rifles. Scopes that cost more then two rifles. What happened to the sportsman and average shooter?
Remember if a guy has one gun, he is deadly but if he has 100 he can't shoot.
I have posted ALL of my groups since I have been on the sites, where are yours? [smilie=1:
I can make a traditional, round ball muzzle loader sit up and talk, funny I get the same static on those sites that I get here. I love the ones shooting WW balls and saying they shoot good! I guess BANG and SMOKE means it all works!
Here are 5 shots at 50 yd from my home made, .54 Hawken. It has shot an inch at 100 and I hit 4 out of 5 steel chickens off hand at 200 meters. I must be wrong and need a super, duper inline shooting pistol bullets and a high power scope. Dang, I must have the wrong twist and ball fit too.

[45 2.1]

Guess I'll have to get me one of those 1/4 inch shooting 450 Marlins like you have so I can really start to understand everything. :coffee:

You have mistaken me with someone else. It would be nice if you would get your "facts" right also. I posted a very nice 0.17" group shot with a 450 Marlin, at high velocity for that cartridge, by BABore some time ago. I said this is what you can do if you know how, not that I did it, your presumption. It would seem you need to read more closely so that you really understand what you read and don't claim somebody did something when they didn't say they did. Perhaps the last sentence of my previous post would make some sense to you now.

[Pat I.]

For a guy that has 4815 posts on this forum alone making a joke about someone getting off their chair is a little strange don't you think?

I didn't know posting groups was part of the game but if you go in the past FS when I was more active everything's there, plus it's more than one group and somebody besides a cow saw me do it.

Don't have any group pictures but do have a picture of some of the guns I use to shoot cast bullets with, does this count??

[45 2.1]

For a guy that has 4815 posts on this forum alone making a joke about someone getting off their chair is a little strange don't you think? Jim made a very good point......for someone who claims to be as good as you are..........it doesn't show.

I didn't know posting groups was part of the game but if you go in the past FS when I was more active everything's there, plus it's more than one group and somebody besides a cow saw me do it.
Whoopie...................... so your a show-off. We aren't, but we're trying to help the other forum members here. What are you doing?

[44man]

Pat, let's go farther. How about an MOA, 7 BR at 100 and 200 yd's?
How about a Wichita, 7 R at 200 yd's?
Son of a gun, I must have the wrong twist and bullet match. All the books I read showed such great 25 yd groups and exactly what powders to use! :mrgreen: How in the world did I ever shoot 40 out of 40 at IHMSA matches? :Fire: I should have kept reading to find the answers.
Your turn, post what you have done.

[Pat I.]

Sorry if I presumed something but this is a quote from an earlier run in I had with you.

" There is the other end of that, ie maybe I have done that and taught others how. Can you run a 35 Whelen at over 2600 fps and put a five or six shot group in under 0.7" at 100 yds. Can you put 5 shots from a 450 Marlin in less than 0.5 MOA at 2250 fps. When you can, then you can say the same things we do. Until then though, I wish you would read some back posts."

Since you didn't attribute the results to someone else I don't think I'm off base by presuming you were the shooter, or just maybe that was the intent. Who's WE by the way, got a mouse in your pocket?

[Pat I.]

Not a show off at all just letting you know you're not talking to some nimrod that's gonna fall for your line of BS.

If you think a good point is made by telling a guy with 378 posts to get off his chair by someone with 4800 you're farther out there than I thought. I don't know how you guys find time to go to the bathroom let alone do all the wondrous things you claim.

Well I did hold a 10 shot 200 yd agg record for a little while and have a bunch of awards from national tournaments, not that that means anything, but you'll notice if you go back and read what I've written in the past I never did claim to be a great shot or make outlandish claims, unlike some.

[45 2.1]

Sorry if I presumed something but this is a quote from an earlier run in I had with you.

" There is the other end of that, ie maybe I have done that and taught others how. Can you run a 35 Whelen at over 2600 fps and put a five or six shot group in under 0.7" at 100 yds. Can you put 5 shots from a 450 Marlin in less than 0.5 MOA at 2250 fps. When you can, then you can say the same things we do. Until then though, I wish you would read some back posts."

Since you didn't attribute the results to someone else I don't think I'm off base by presuming you were the shooter, or just maybe that was the intent. Who's WE by the way, got a mouse in your pocket?

I don't keep rodents, I kill them. Had you of read somewhat more, you would have known that those were groups by BABore and 357 Maximum. I shoot the 4570 into somewhat better groups at somewhat slower velocity more in range with comfort. Besides, millions of buffalo were killed with the same ballistics out of the 4570. Both of them would be somewhat shorter and blunter to someone who doesn't understand what he reads and calls people liars. You really need to understand what you read instead of taking things out of context. That is becoming a real habit with you.

Not a show off at all just letting you know you're not talking to some nimrod that's gonna fall for your line of BS. Nimrod is a valid comparison. Nimrod of the Bible is the one.

If you think a good point is made by telling a guy with 378 posts to get off his chair by someone with 4800 you're farther out there than I thought. I don't know how you guys find time to go to the bathroom let alone do all the wondrous things you claim. Jims been around longer than you. I on the other hand started young and shot a lot. To bad your experience didn't give you much to write about.

Well I did hold a 10 shot 200 yd agg record for a little while and have a bunch of awards from national tournaments, not that that means anything, but you'll notice if you go back and read what I've written in the past I never did claim to be a great shot or make outlandish claims, unlike some. It seems you just did, against how many shooters? Jims accomplishments are a matter of record. To bad you can't do something outlandish, maybe your eyes could see then

[44man]

Hee, hee, armchair shooters are again saying I am lying and only cows watch me shoot! :drinks:
Too bad I no longer have the eyesight I had when I shot these groups. Years take a toll and I have forgotten more then most ever learn in a lifetime unless it comes from a book. I just wish I had kept ALL of the groups I have shot. There was no internet back then. Guns come and go and I had no reason to keep groups to prove anything.
I am really sorry I didn't learn more about guns, maybe I could have done better! :Fire:
Guess what, I did it on the cheap with factory stuff, not $100,000 worth of switch barrel stuff and custom stocks and actions. Plain old Hornady bullets and cast boolits.

[Pat I.]

You really need to understand what you read instead of taking things out of context.

And here I thought the point was to not believe anything you read. Pick a side sport because it's not me that doesn't understand, I understand fully.

[44man]

45 2.1, notice I am now on the ignore list? No proof is forthcoming! :drinks: