New 1:14 twist 30-06

[FAsmus]

Larry;

I will have to show my ignorance here, but so be it.

In this cast bullet game I've always heard the velocity itself was the limiting factor, not the RPM of the bullet. ~ Sure alloy, lube, hardness and bullet quality all enter in but the limiting factor always seemed to be bullet strength - or the inability of lead alloys to resist the heat and friction of the travel through the barrel after a certain velocity.

Please tell us, if you have the time, why jacketed bullets don't run into the same RPM limitation.

Good morning,
Forrest

[singleshot]

FAsmus,

Not being Larry, I'll still give the obvious answer. Jacketed bullets absolutely have an RPM limit. Here's a story to illustrate: I had a friend who was a competitive HP rifle shooter a handful of years ago who missed the Olympic Team by 2 slots. Anyway, he was manning the target pits one day, and another friend was on the line. As his friend shot, he could hear the sound of the bullet, then a very unfamiliar buzzing and whirring sound with each shot as the rounds travelled overhead. Lo and behold, none of the shots hit the target. Upon further investigation, they discovered that each bullet was breaking apart before it got to the target. His friend had been shooting his new fast-twist toy (don't remember specifics.) They realized the bullet was disassembling, not being able to withstand the RPM's they were pushed to. In the end, the friend had to swap in a slower twist barrel, and never had another problem. As stated before, this is simple physics and EVERY material has ultimate yield points where the material simply fails.

[Larry Gibson]

FAsmus,

Not being Larry, I'll still give the obvious answer. Jacketed bullets absolutely have an RPM limit.......

Single shot is correct. Not only do jacketed bullets have a "limit" when they spin apart but they also have a threshold where accuracy will deteriorate in a non-linear fashion.....just like cast bullets and PP'd for that matter. Jacketed bullets maintain their balance under acceleration much better than cast bullets. Thus the RPM threshold for jacketed is much higher, many time higher than the velocity attainable by the cartridge. Ever wonder why milsurp bullets aren't as accurate as commercial hunting bullets which many times aren't as accurate as match bullets? It's simply a matter of the jacket being concentric in thickness and form, the lead alloy being uniform in weight and swaged into the jacket with no air pockets of the commercial hunting and match bullets that make them more balanced in form (center of gravity/mass coinciding with center of form) that makes them more accurate.

Ran a test way back in the beginning of this RPM threshold discussion for bass ackwards to prove the point. I drilled a small hole in the side of some M118 match ammunition unbalancing them to a large degree so that the RPM threshold would be lower than the produced RPM. The test was conducted at 50 yards, 100 yards and 200 yards. 10 shots of unmodified M118 were shot at each range for group and 10 shots of the modified also for group. The groups with the unmodified M118 were consistent and exhibited linear expansion of group size between 50, 100 and 200 yards. The unmodified M118 group at 200 yards was just at 2 times the size of the 100 yard group just as it should have been. The modified M118 groups were larger and non-linear between 50, 100 and 200 yard groups. The modified M118 group at 200 yards was actually 3+ times larger than the 100 yard group. That is definitely non-linear and a sure sign the RPM threshold was crossed.

Velocity is not the limiting factor many think it is. Take cast bullets in 7, 9, 12 and 14" twist .223 Remingtons or 10, 12 and 14" twist .308Ws for example. Cast bullets can be driven to higher velocity in each with equal accuracy as the twist becomes slower. I can get 1 - 1.5 moa accuracy out of a 311466 consistently at 1900 - 2000 fps out of most any 10" twist .308W. I can get the same 1 - 1.5 moa consistent accuracy out of 12" twist .308Ws at 2200 - 2300+ fps. I can get the same 1 - 1.5 moa out of 14" twist .308Ws at 2600+ fps. Same bullet, same cartridge, same accuracy but different velocities. If you do the math though you'll find the RPM is close to the same for all velocities. Same holds true for the different twists with cast bullets in .223. It is the RPM.

Larry Gibson

[RoyEllis]

FAsmus,

Not being Larry, I'll still give the obvious answer. Jacketed bullets absolutely have an RPM limit...... They realized the bullet was disassembling, not being able to withstand the RPM's they were pushed to. In the end, the friend had to swap in a slower twist barrel, and never had another problem. As stated before, this is simple physics and EVERY material has ultimate yield points where the material simply fails.

I've personally seen and done this very thing with a 22/250 and thin jacketed varmint bullets...the spotter could see the puff as they blew apart in mid-air. So no matter what what claims the unwashed make, YES Virginia....there is a rpm threshold. It's not some arcane BS theory for Don Quixote's to tilt at but a simple law of physics. Every solid material known to man has a limit to stress induced by rotational forces, it isn't a "brick wall" type of thing as grain structure and molecular bonding of individual samples of 1 material can vary. BUT there is a range of stress that is the redline of impending stress failure. This is, I believe, what Larry has been so patiently attempting to explain even though some are he!!-bent on their own deviant troll agenda.

[felix]

Circumferential speed is dependent on the projectile's radius as we all know. Based upon that thought, is it the circumference speed or the functional radius (RPM) treated as the pivot for the accuracy limitation amongst the two parameters? I maintain it's the circumferential speed as the "real" limiting factor. But, for our argument they can be considered the same because of the dependency of all the factors we know about upon one another (incest, if you will). ... felix

[singleshot]

Circumferential speed is dependent on the projectile's radius as we all know. Based upon that thought, is it the circumference speed or the functional radius (RPM) treated as the pivot for the accuracy limitation amongst the two parameters? I maintain it's the circumferential speed as the "real" limiting factor. But, for our argument they can be considered the same because of the dependency of all the factors we know about upon one another (incest, if you will). ... felix

I agree. My own testing and experience indicate that smaller projectiles can be spun at higher RPMs and larger projectiles must have lower RPMs. Forces on the projectile are dependent upon the circumference of said projectile, simple physics.

[Green Lizzard]

nobade i wish all my 30s were 14 twist

[TXGunNut]

nobade i wish all my 30s were 14 twist

True That! Have a couple of pretty nice 1:10 30-06's that will probably never be uncased on a hunting trip or taken for a casual day at the range because keeping boolits under the threshold for these rifles simply doesn't interest me. They'll always shoot j-words and I'd rather shoot boolits. I have too many other rifles that I'd rather hunt or piddle with. Sad, very sad.

[Green Lizzard]

hey tx my 788 30-30 would work trying to get to 1850, real hard alloy maybe 2000 but my old 35 rem with 16 twist no problem even with 20 to 1 alloy

[TXGunNut]

hey tx my 788 30-30 would work trying to get to 1850, real hard alloy maybe 2000 but my old 35 rem with 16 twist no problem even with 20 to 1 alloy

Yes, my 35 Rem even seems to prefer softer boolits but I don't push it much over 2000 fps. She's headed to the range with me after another cup of coffee!

[Larry Gibson]

With a 16" twist 35 Rem one would have to use a very, very light weight cast bullet to even approach the RPM threshold. Doubt I could do it in my 26" barreled 35 Rem.....not enough case capacity and too small an expansion ratio.

Larry Gibson

[TXGunNut]

With a 16" twist 35 Rem one would have to use a very, very light weight cast bullet to even approach the RPM threshold. Doubt I could do it in my 26" barreled 35 Rem.....not enough case capacity and too small an expansion ratio.

Larry Gibson

It would seem to take a very fast load to cross that threshold but my 336 is happier with 190 gr boolits under 2100 fps for some reason. With the right powder I might be able to make it to 2200, just haven't seen the need. Still need to get off my **** and head for the range!

[Larry Gibson]

It would seem to take a very fast load to cross that threshold but my 336 is happier with 190 gr boolits under 2100 fps for some reason. With the right powder I might be able to make it to 2200, just haven't seen the need. Still need to get off my **** and head for the range!

My 35 Rem is also real "happy" with the 200 gr RCBS bullet at 2150 fps. That's as fast as it gets simply because that is at 100% load density with 4895. Suppose I could change powder but I haven't seen the need either. I do keep swearing I'll test that bullet with LeveRevolution powder just to see what it will do. However, I too must get off my **** and get to it......maybe one of these days.

Larry Gibson

[Green Lizzard]

thats the same bullet i use larry, i tell everyone that it was the easiest rifle i ever developed a cast load for. seemed that every thing i tried in it worked, but 4895 and 4759 stood out

[MBTcustom]

Not trying to tell anybody what's what, but some of this is very confusing to me. I know from my own knowledge of how things work, that any object has an RPM threshold, or point where it is no longer able to sustain itself in a balanced condition. Like spinning a top, the faster you go, there will be a point where the strain of inertia overcomes the gyroscopic effect that keeps it stable.
I also know that the point at which everything falls apart is greatly extended by the object being properly balanced.

The RPM theory holds that a cast boolit will no longer be able to keep itself together past about 140,000rpms (forgive me if that is wrong) because the alloy tries to sling itself apart in mid air which creates a compounding problem that deteriorates accuracy very quickly. (ie, once that boolit gets a little janky from the forces of inertia, it's all over but the cryin)

I would support that theory totally, because some of my own experience seems to back it up.
Unfortunately, (or perhaps fortunately) I have also seen evidence that suggests there is more to the story.
You might remember that the original reason I came here was to learn how to paper patch smokeless rifle boolits? I have seen the theoretical RPM threshold absolutely thrashed by paper patched boolits. This is common knowledge. One guy even pushed 180 grain cast boolits to 3000FPS with MOA accuracy in his 300winmag.
The point is, it's still a cast lead boolit of similar design, and of similar hardness, with the only change being the addition of a paper jacket (which, unlike a copper jacket, does nothing to improve the theoretical RPM limit of the cast lead boolit).
If the RPM theory is correct, why does a wisp of paper disprove it so consistently?

Again, I'm not saying that the RPM theory doesn't ever apply, but to use it to explain why a cast lead boolit bites it at about 140,000 to 160,000 seems like we may be in danger of glossing over a problem with an easy answer.

It reminds me of a story told to me by a professional forester a few months ago.
He told me that at one time it was commonly held that when pecan trees stopped producing, it was because they were lacking iron. To resupply the tree's with this "necessary" mineral, the owners were encouraged to pound a bunch of nails in the trunk of the tree, which would give it what it lacked. Sure enough, they would hammer nails into the tree and their superstition was reinforced with an abundant crop of pecans in short order.
It wasn't until many years later, with the help of science and good botany that it was discovered that the trees didn't need iron at all! By hammering in a bunch of nails, the tree was stressed, and it tried to reproduce it'self, thus bearing fruit.
The evidence consistently supported the belief, and there were folks that would get into all out table slapping arguments like we do on this issue.
Turns out, there were much less invasive ways to coax the trees into good harvest that didn't involve filling the trunk with nails, but it wasn't the folks with the hammer that discovered this, it was the scientists.

[Char-Gar]

I don't have a science bone or brain cell in my body, but always supposed that cast bullets are scored and have metal displaced by the rifling and this was a factor in the bullets losing accuracy after the bullet reached a certain RPM range. After the effect of rifling, the bullet is no longer round, but has a series of fins if you will to catch air as it whirls.

A cast paper patched bullet is not scored by the rifling. The paper takes that beating and the bullet exists the barrel round and without the fins to catch the air as it whirls.

I have always thought this was the reason a paper patched bullet can be fired faster which imparts more RMPs without having bad things happen to it. I have no reason to know this is true, but it just seem intuitive to me.

As an aside, Texans have long "thrashed" pecan trees to stress them and encourage the to produce more fruit. They usually do it with a long pole of some kind.

[MBTcustom]

I don't have a science bone or brain cell in my body, but always supposed that cast bullets are scored and have metal displaced by the rifling and this was a factor in the bullets losing accuracy after the bullet reached a certain RPM range. After the effect of rifling, the bullet is no longer round, but has a series of fins if you will to catch air as it whirls.


A cast paper patched bullet is not scored by the rifling. The paper takes that beating and the bullet exists the barrel round and without the fins to catch the air as it whirls.

I have always thought this was the reason a paper patched bullet can be fired faster which imparts more RMPs without having bad things happen to it. I have no reason to know this is true, but it just seem intuitive to me.

I'd be willing to go along with that char-gar, but that's not RPM getting you, that's boolit deformation. If that were the case, then why not shoot a barrel with polygonal rifling, and boost the RPM threshold to a more desirable level? That's not an RPM wall, that's boolit trouble.
Why would you drive down the freeway with flat tires, and blame the Chevy for being a lousy design, or say something like: "if I was driving a corvette, I could do 60MPH easily, but you can't expect that out of a pickup truck".
Why would anyone attribute a boolit problem to RPM? It just doesn't make sense.
Yeah, a Corvette will beat a pickup truck in a race, but what's that got to do with flat tires, and why would that ever be part of the discussion for your lousy gas mileage, or noisy ride to work?

[Dthunter]

Hello guys! Been working up a storm!
Looks like discussions got heated!

O well! All I know is that a rifle built with all of its components aligned and tight fitting is obviously going to have a better chance to shoot well. I have built barrels and custom rifles for a few years myself. And its fun as heck!

But as I have said all along, the limitation is our boolet alloy, and the physical forces imparted on it.

"One" of the reasons i feel the paper patch bullets fair better is that they leave the bore in the same condition "EXACTLY THE SAME" as they start. Provided the load/rifle doesnt cause the supported boolet to encounter an alloy "yielding" force. The paper supports suprisingly well!
A conventionally fired cast boolet has been directly engraved by the rifling and has some rifling grooves cut into it. This imparted "mechanical" aspect can cause issues to the integrity of the overall boolet. Just some food for thought.

[felix]

No seams on a baseball, no curve balls. Just that little disturbance on the ball causes hitters to go bananas. A ball with no spin will dart unpredictably upon any kind of non-uniform disturbance during its travel. Paper coatings rebound enough or just fly off and that eliminates enough of the rifling seams. Then the remaining boolit should be rotating enough to mimic the baseball fast ball. ... felix

[45 2.1]

All you guys who are say the PP boolit doesn't have rifling marks on it need to recover some of them. Unless it's steel it's going to have rifling engraved on it..... BTDT.................... however, you're free to believe anything else you want to.