Boolit Stability... Facts and Fiction

[45 2.1]

There is a lot of controversy about this subject. The Dec-Jan issue of Reloader Magazine has an article by John Barsness relating some very interesting things about this. A short form of the article can be seen here: http://forums.accuratereloading.com/eve/forums/a/tpc/f/1811043/m/6021000181
but the original in Reloader magazine is prefered due to the pictures shown.

It would seem folks have trouble with cast from not casting a good boolit. Myself i'm with the results in Reloader magazine.

Your opinions?

[Larry Gibson]

Excellent quote the author (Brian Litz) uses at the beginning; The home page of his website, www.appliedballisticsllc.com, has a quote from Yogi Berra: “In theory there is no difference between theory and practice. But in practice, there is.”

However, the author would have been somewhat more informative had he explained that “stabilization” of a bullet is generally referred to as over stabilized, stabilized and minimally stabilized. Understand that in all three cases the bullets are stabilized enough for point forward flight. [Perhaps the author does allude to that but the poster of the quotes does not].

“In fact, a rifling twist just enough to stabilize a bullet causes far more problems than the nonexistent tragedy of overstabilization.” A generalized statement true if the twist only marginally stabilizes the bullet or a bullet too heavy/long for the twist is used. If one uses a bullet too long or heavy for the twist and the bullet is not stabilized properly or minimally is it really the fault of the twist (?) or is actually the fault of the user for using the wrong bullet? The author then goes on a long dissertation about 120 gr bullet, 10” twist and 25 caliber 250’s……he makes an excellent point with that discussion about using a too heavy bullet the 117 – 120 gr bullets in the original 14” twist of the 250 Savage. He did however discuss the 87 -100 gr bullet and how the 14” twist was made for them. The choice of the 14” twist for the original 250 Savage was made because it “stabilized the 87 and 100 gr bullets originally loaded in that cartridge. The use of 117 and 120 gr bullets proved unsatisfactory as the bullet were marginally stabilized at best. Classic case of wrong bullet for the twist.

Many tests of accuracy and of measuring the BCs of fired bullets clearly demonstrate that each bullet will perform best with a certain twist. Many bullets perform well, especially the well made and balanced Berger bullets for who the author works, also shoot well in a range of twists. However, there is one twist rate it will do best ate. This is why, in the 223 for example, there is a myriad of twists available. This is so the twist can be balanced against the intended match bullet for best stabilization and accuracy. All of which agrees with the author.

Here in lays the two keys to the authors premise;

“Bryan wrote that there’s a tiny particle of truth to the notion of overstabilization, but the effects have been greatly exaggerated. He cited various examples showing that a well-balanced target bullet the effect is so small it can’t be seen in 1,000-yard shooting.”

“These days most bullets are so well balanced many rifle manufacturers have started using much faster twists in their barrels, allowing shooters greater flexibility in bullet weight and length.

Note the “with a well-balanced target bullet” and the “bullets are so well balanced” part. Assuming all this has to do with cast bullets at high velocity then the key is, as I and several others have stated numerous times, to get the cast bullet as balanced as possible during casting, keep it that way during loading and to use every means to lessen the damage done during acceleration phase (internal ballistics). The better the bullet is balanced in flight (external ballistics) then the less adverse affect the centrifugal force of the RPM has on the bullet. For a given cast bullet with any imbalance at a given velocity the lesser the RPM the more accurate the cast bullet will be, or any bullet for that matter.

Larry Gibson

[geargnasher]

I tend to agree with the article's author as well, and will add that aerodynamic flaws induced through the launching process probably have more effect on cast boolit stability downrange than physical balance issues such as internal voids.

Gear

[williamwaco]

I have heard of over stabilization my entire reloading life.

I have tried several times to produce it but I have never seen it.

My first attempt was with the .243 with the 60 gr bullet, then the .270 with the 90 grain, then the .22-250 with the 40 grain.

All were superbly accurate at the highest velocities I could obtain.

Somewhere around 38 / 3900 fps ( didn't have chronographs in those days. ) The 40 gr Hornet bullet in the .22-250, just vaporized. It left a trail of grey smoke down the range and a splatter of grey lead dots about the size of this " . " on the paper but no hole.

I know the twist in the .243 was 1 in 10. Don't know the others.

On the other end of the spectrum, I have seen many instances of oval shaped holes from bullets at long distances after they have slowed down. Especially handgun bullets.

Somebody hazard a guess. What velocity would be required to over stabilize a 60 grain .243 bullet in a 10" twist?



.

[**oneshot**]

I'll leave this one to the experts. At the velocities and weight for caliber I shoot, I don't think I will even over-stabilize a boolit.

[fecmech]

Somebody hazard a guess. What velocity would be required to over stabilize a 60 grain .243 bullet in a 10" twist?
I know it's more than 3800 fps. Back "in the day" with my .243 Remington 788 I simply filled cases with H380, put a 60 gr Sierra on top and could stay 1/2-3/4" all day long on demand. I shot that bullet with Red Dot @1200 fps, 4227@ 1900 fps and the H380 in the 3600-3800 fps range, it was boringly accurate( time frame was early 70's).

[mpmarty]

Well yesterday I went out fully loaded with gear: One spotting scope w/ tripod, One chronograph with tripod, Savage 308 bolt gun and a box of fresh reloads using 175 gr cast 31141s and 25gr of 2400 in LC Match cases. Fired two over the chrono and got 2250 and 2275 fps. Fired two at target at 100 yards and got two "Xs" overlapping each other. I'm a happy camper and don't worry about my "fast" 1 in 10 barrel.

[4570guy]

I have personally observed small bullets fired too fast. I know for a fact that they were not coming apart as we found bullet holes in paper - and impact points all over the berm. In this particular case they were 50 gr Sierra's fired from an AR-15. This was a friend's rifle and I don't recall the twist rate, but I think it was 1:9. 55 gr bullets (and heavier) were superbly accurate from this rifle. When we tried some left over 50 grainer's that I had on hand, they were literally impacting all over the berm on our 100 yard range. Some struck low, some high, some far left & right. Some time back I read a paper on bullet stability boundaries. We all know about spin rates too slow - turns out you can spin them too fast as well causing stability issues.

[HangFireW8]

You can see the affects of overstabilization with a 0.1MOA 6mm PPC rifle shooting flat-based bullets up to 300 Meters with several barrels with tight and loose twists.

You cannot see it with a cartridge like 250/3000. At all.

You are unlikely to see it with boat-tail bullets at long range, at all.

Sorry, no opinions 45 2.1, just facts.

HF

[brotherdarrell]

I don't know much about nuthin, but I do know I shot 40 gr sierra hp's out of a 1:9 twist Savage .223 (26" barrel) that would stay under moa out to 300 yds. The chrono read over 3900 fps. Also had a 1:9 twist AR that would keep 50 gr. dogtown s.points under moa. Not exactly apples to apples but it does tell me maybe I need to make better boolits.

Just my experience and observations.

brotherdarrll

[Larry Gibson]

brotherdarrell

How well do you think or know would 68 or 69 gr mach bullets shoot out of that 9" twist Savage? I ask because my Savage Comp Match rifle with 26" barrel with 9" twist will also shoot 40- 50 gr j bullets about that fast and with about the same moa accuracy. However, 69 gr MKs at 2950 - 3200 fps will shoot into .2 - .3 moa........wonder if it's becase they are more "balanced" bullets and are perhaps better suited to the 9" twist?

Larry Gibson

[Bullshop]

Something to think about when considering twist rate besides bullet stability is atainable velocity.
In most cases at equal pressure a faster twist will have a lower velocity than a slower twist barrel. A good example is/was the 250 Savage. They wanted to introduce a factory cartridge with an then unheard of velocity of 3000 fps with an 87gn bullet. They had to go with a 1/14" twist to reach the desired velocity.
Almost all 25 cal barrels today are 1/10" twist. Can you get 3000 fps with 87gn bullet from a 250 Savage at NORMAL pressure? They couldnt.
Another good example is the 22 Cheeta. The Cheeta was designed to shoot what were considered conventional weight bullets for 22 cal 50 to 55gn. It was intended to shoot them as fast as could be practically expected. It uses a 1/16" twist for the same reason, highest possible velocity with adequate stability
So twist is not only about stability but also velocity. You guys with the super fast twist barrels may not want to hear it or believe it but you are sacrificing velocity if you load to normal pressure.

[brotherdarrell]

brotherdarrell

How well do you think or know would 68 or 69 gr mach bullets shoot out of that 9" twist Savage? I ask because my Savage Comp Match rifle with 26" barrel with 9" twist will also shoot 40- 50 gr j bullets about that fast and with about the same moa accuracy. However, 69 gr MKs at 2950 - 3200 fps will shoot into .2 - .3 moa........wonder if it's becase they are more "balanced" bullets and are perhaps better suited to the 9" twist?

Larry Gibson

Larry, most of my shooting with the Savage was with the smaller bullets as my main intent was for predator hunting. I did play with the 68 gr match bullets just to see what they/I was capable of. I was able to keep these well under .5 moa @ 100 yds but I would guess that my shooting capabilities was not up to the task to completely wring out the possibilities of the combination. While I do have a good chunk of german blood ( read anal/retentiveness) I have much more redneck in me and minute of ground squirrel is generally where I stop.

As to why the longer bullets do better, you got me. I would assume ( :shock:) that the combination is just inherently conducive to accuracy/precision. But, again, this is just conjecture on my part as my knowledge/experience in this area is purely layman and pales in comparison to many on this site. (If you want to discuss the finer points of tying a #24 trico midge or the personality traits of chimps these I have strong opinions on:veryconfu)

One more experience with "over-stablization": Ruger m77 .243, case full of Varget and 58 gr. v-max would stay under 2" @ 300 yds for 3 shot groups out of a pencil thin 20" 1:10" barrel. I can only go with what I have seen/experienced, which pretty much tracks with what you have been stating all along. I am a firm believer in proving a theory by "failing to dis-prove" the theory (MS in biology/wildlife science) and due to the fact that other theories are ephemeral at best I have to go with what I have available.

brotherdarrell

[brotherdarrell]

Another thing I found was with my .222 rem and 55 gr. Berger match bullets. Moa. @ 200 yds. was consistently smaller than at 100 yds. I had heard of this and experienced it for myself and it only showed with the Berger bullet.

Just another wrinkle to add to the equation.

brotherdarrell

[44man]

I did not read the whole article but it seems it is right on. I have always wanted a faster twist for long range with my varmint rifles because a longer bullet shot better and carried better. Rifle shooting has gone by the wayside for me since I went more to the revolver using heavier hunting boolits.
Yet the same thing shows up, slow twists give out if the boolit can not be driven fast enough. Too many revolvers have rates too slow. You need lighter, shorter boolits for slow twists.
Take the Freedom .475 with a 1 in 18" rate and the Ruger .480 with a 1 in 18-3/4". Both do better at the lighter boolit range for extreme accuracy, yeah I know some try to shoot a 460 gr boolit! I feel they top at 400 gr.
Take the BFR with a 1 in 15", accuracy just starts at 400 and can shoot very heavy boolits. It seems the range of weights will go up with a faster twist.
Then the Ruger .44 with 1 in 20", it tops at about 330 gr but will really shoot 240 to 330. Not good with 180 or 200 gr. Marlin thought the additional velocity from the rifle needed 1 in 38" but the boolit can not be driven, it failed in the .444.
Twist is so important for a bullet/boolit, velocity match.
Many discount the revolver but it works the same as a rifle.
I love a little faster twist but you can go too fast the same as going too slow.
I read Larry, Gear and Bullshop and a few others that have knowledge I would depend on.
45 2.1 and I do have a few things between us, I don't know why but he is right and I agree MOST of the time. Call it 99%! Only revolver boolit start seems to be a sticking point between us. :mrgreen:
Twist is just too important and even in the .22's, you can not shoot 40 to 70 gr in the same twist.
Back in the time I never wanted a 22-250 because the rate did not allow a heavy bullet. The lighter bullets reduced range while I shot chucks in the head over 600 yards with the 220 Swift with 60 gr bullets. That bullet would not group at 100 at all, did not go to sleep from the fast spin.
I have always felt it is distance that dictates twist. If you want 1000 yards, do not work loads at 100, you will pull your hair, it can't be done. Watch bullets with a scope, if it rotates around the flight path close it is better at long range. A sleeping boolit at 100 will fail at long range.
1/2" at 100, 1" at 200, 2" at 400 and on and on is just a joke. If you shoot 1" at 400, the group will be LARGER at 100.

[Larry Gibson]

brotherdarrell

Good post.

Larry, most of my shooting with the Savage was with the smaller bullets as my main intent was for predator hunting. I did play with the 68 gr match bullets just to see what they/I was capable of. I was able to keep these well under .5 moa @ 100 yds but I would guess that my shooting capabilities was not up to the task to completely wring out the possibilities of the combination. While I do have a good chunk of german blood ( read anal/retentiveness) I have much more redneck in me and minute of ground squirrel is generally where I stop. Nothing wrong with that concept of accuracy. I also stop when I achieve the desired results. In my younger days i shot up a lot of componants and shot out a couple barrel searching for that alusive "more accurate" load.

As to why the longer bullets do better, you got me. I would assume ( :shock:) that the combination is just inherently conducive to accuracy/precision. Very good assumption on your part. It is the combination of a better bullet and a bullet weight/length more suited/matched to the twist that produces better accuracy.

But, again, this is just conjecture on my part as my knowledge/experience in this area is purely layman and pales in comparison to many on this site. (If you want to discuss the finer points of tying a #24 trico midge or the personality traits of chimps these I have strong opinions on:veryconfu)Not me.....that's 45 2.1's forte'.

One more experience with "over-stablization": Ruger m77 .243, case full of Varget and 58 gr. v-max would stay under 2" @ 300 yds for 3 shot groups out of a pencil thin 20" 1:10" barrel. I can only go with what I have seen/experienced, which pretty much tracks with what you have been stating all along. I am a firm believer in proving a theory by "failing to dis-prove" the theory (MS in biology/wildlife science) and due to the fact that other theories are ephemeral at best I have to go with what I have available.ood example but keep in mind a 10" twist is not a lot of "overstabilization" in the .243. If the twist was faster then perhaps. Many bullets actually have a "twist range" where, within certain velocity ranges, they are quite accurate. As I noted in a post above the trick is to keep them balanced in manufacture, loading and accelleration. The higher the RPM the higher the inaccuracy from any imbalance is magnified. With the .223 at a given velocity for example; a 7" twist barrel will produce twice as many RPM as a 14" twist. Thus the centrafugal force on the bullet from the 7" twist. Any imbalance in that bullet is thus acted upon much more.

Larry Gibson

[Dean D.]

This is a good thread, lets not let it devolve into a juvenile urinating contest. Problems created or happening on other websites need to stay there, don't bring them here. The only thing that results from doing so is that everyone loses out on good info.

Honestly, no one here CARES about quarrels happening on other websites, if we want to read that kind of garbage we can go to those other websites.

KEEP IT OFF CAST BOOLITS