twist rates and end results

Elvis · Posted: Sat Dec 17, 2016 9:31 am Post subject: twist rates and end results

Ok lads n lasses Im hopeing some of you will have mulled this one over and come to some sort of meaningful educated conclusions...... surely our guru of projectile testing Slimjim will have photos and the like to back up his hypothosis (hows that for a wheelbarrow word at 9;20am???? Very Happy

)

on another site I regularly visit we having healthy discussion on the effects of different twist rates on terminal preformance

personaly I believe the faster the twist the quicker the projectile must open up...going to the extreme of .220 swift where you can blow projectile to bits in mid ai Shocked

r....
the .22/250 has slow twist rate so the light varmit pills will hold together ....

so have any of you lads with front stuffer .45s tried same projectile at same velocity in your slow twist BP rifle and also in faster twist .45/70 ?????
and if so was there a major difference in terminal preformance????

or maybe in .22 centrefire fast twist AR and also in say .222 rem with thier 1 in 14 slow twist barrels.

I know you need faster twist to "stabalize" a heavier projectile but its the Scratch

fragility (for want of better word) of projectile upon impact we are talking about here.

the awesome 50 grn spsx projectiles I used a year or so back in .223 were recomended for below 3000 fps
maybe we will one day soon see maximum twist rate too, we have minimums on projectile boxes already.

Grumulkin · Posted: Sat Dec 17, 2016 12:48 pm Post subject: Re: twist rates and end results

I think you'll have difficulty finding anyone who has tested terminal performance in fast twist versus slow twist barrels with the same bullet at the same velocity. Some of my thoughts are:

1. It makes sense that a bullet that was on the edge of self destructing (because of a fast twist) while flying through the air because of a fast twist would disintegrate on hitting flesh. Alternatively if the bullet disintegrated in the air it would have no terminal performance.

2. The bullets said to disintegrate in the air would be light varmint bullets with thin jackets. If the bullet was a bronze or copper monometal bullet, it wouldn't disintegrate no matter what the velocity or twist was and, in my opinion, the only significant factor in terminal performance would be velocity and not how fast the bullet was spinning.

3. I can't imagine that any muzzle loader would have a high enough velocity to see any difference in terminal performance no matter how different the twists would be. Also, you would probably not even be able to buy one with a twist even close to where a projectile would be expected to disintegrate.

PaulS · Posted: Sat Dec 17, 2016 1:27 pm Post subject: Re: twist rates and end results

With modern bullet construction the twist rates that are common, in and of themselves, are unlikely to cause disintegration. Velocities above 3500 fps generate heat on the bullet as it travels through the air, beginning at the nose and working its way back to the body. This heat is most often the reason for disintegrating rounds and not the rate of spin alone. Bullet cores and their jackets are strong enough to expand slowly under the impact with game yet stay together with very fast twist rates. The 223/5,56 is a good example of this. You can fire a 50 grain bullet from a 1:7 twist and it stays together yet a 220 Swift will shoot that same bullet with a slower twist and it will not make it to the target. The difference is the velocity. At 3000 fps the heat is low but when you push it to 3900 fps the bullet will heat enough to become soft and pliable. The velocity difference is about the speed of sound so instead of going mach 3,x the bullet is traveling at mach 4,x. Even though the rotational speed is less it will destroy the bullet.

Terminal ballistics when hitting soft tissue doesn't generate much heat so the bullet decelerates and expands as it is designed to. Hitting bone or other hard tissue can generate heat as the bullet is radically deformed but the bone will usually deform as well allowing the bullet to continue on to do its job. Hitting something that does not give, like a steel plate, destroys the bullet from the heat generated by the impact. A faster twist may assist in the bullets deformation on impact with any target but I doubt there is a reliable way to measure it. I have fired pistol bullets from a rifle at 2700+ fps and not only did they make it to the target the were remarkably accurate. That is shooting a bullet designed for a 1:16 twist from a 1:10 twist at twice the expected velocity range for the bullet. I never tested the terminal ballistics with it at that velocity and it is likely under these extremes it would "blow up" on impact but it is a good reason to get the Fackler box rebuilt.

That is my considered opinion anyway.

Vince · Posted: Sat Dec 17, 2016 1:40 pm Post subject: Re: twist rates and end results

I tend to agree with Grumps...terminal performance relies on the velocity of the projectile, the bullet/jacket construction and the manufacturers designed expansion rate at a given velocity.

It's my understanding that the twist rate really only comes into play if and when a projectile is driven well beyond it's intended maximum velocity. As Grumps said, a projectile that holds together at a spin rate that is approaching it's destructive threshold hits the target medium, the resulting deformation of the projectile would cause it to 'grenade' on impact with little or no penetration.

Elvis · Posted: Sat Dec 17, 2016 3:35 pm Post subject: Re: twist rates and end results

yips thats eggzachary my point...... Vince if its 'spinning at close to destruction" the velocity is not the issue.... its the speed of spin.

grumps I was thinking along the lines of Dallanc with his inline muzzle loader with its slow twist and using the same projectile in a different rifle like a .45/70

with modern trends to use fast twists for heavy weight projectiles these fellas must be getting close to limits with a lighter weight projectile..even though the velocity wont be any faster the spin will be considerably more and therefore the projectile should be under considerably more "strain" if my conculations are correct.

Elvis · Posted: Sat Dec 17, 2016 3:39 pm Post subject: Re: twist rates and end results

Paul your 223/5.56 with its 1:7 twist vs mine with its 1: 10 is spinning that pill at 30%??? greater rate of spin is it not??? does this make it more fragile??? is I guess the question we are asking
thats probably the easiest way to measure it 30% increase in spin Vs 30% increase of velocity which we know makes a huge difference.

Grumulkin · Posted: Sat Dec 17, 2016 4:04 pm Post subject: Re: twist rates and end results

Hornady came up with the ELD Match bullet which has a "heat shield" because they found that the plastic tip on the bullets was melting and changing the ballistic coefficient. The bullets, however, don't start to heat up enough to melt the plastic tips until about 300 yards down range and they have to be fired at high velocity.

From what I've read about bullets disintigrating in flight, what is seen is a gray mist with nothing reaching the target which is much less than 300 yards away. So, I don't believe bullet heating is what causes bullet disintegration but rather a fast twist in a relatively fragile high velocity bullet.

Elvis · Posted: Sat Dec 17, 2016 5:17 pm Post subject: Re: twist rates and end results

thats what thinking is happening too
just thought of another of our members who may well know
Gelandagan with his aac/blackout which has very fast twist
now a sierra 125grn hp designed for .30/30 winchester would be a near perfect test projectile
they become granades in the .308 winchester with increase in speed of around 5-700 fps
they are potent enough in my 7.62x39mm
the proof of the pudding as it was would be how much they expand/how deep they manage to penertrate in the fast twist AAC/Blackout at say 2700fps
then do same from slower twist of say a .30/30 or .308
I predict they will grenade at the slower speed if twist is sped up

also Gel will know if the faster twist makes leading of barrel an issue quicker???? the rifling stripping projectile as forces get too much....

Pumpkinslinger · Posted: Sun Dec 18, 2016 3:41 am Post subject: Re: twist rates and end results

en.wikipedia.org/wiki/..._Greenhill

From "Understanding Firearm Ballistics" by R. Rinker, page 344:
"People frequently wonder if bullet spin has any effect on killing power. The simple answer is yes, but the amount is very small and the explanation is not simple." There's more in there, including some math regarding bullet spin related to terminal performance.

gelandangan · Posted: Sun Dec 18, 2016 10:33 am Post subject: Re: twist rates and end results

Now after a few years of usage, I do wish I did not use such a fast twist on my 300 Whisper.
Average Ozzie shooters cannot access sound moderator for their guns, thus the moot point of using 240 grain plus projectile where fast twists are needed to stabilize the long pellet at low subsonic velocity. Using the fast twist with light projectile (110 - 130 gn) to higher end of supersonic velocity (2600 fps or more) might (and did in my case) cause the projectile to explode as soon as it leave the barrel.
I am now resorting to more expensive brand since they are better constructed and less likely to explode on the way, and I have no longer loaded my Whisper to subsonics.

PaulS · Posted: Sun Dec 18, 2016 3:02 pm Post subject: Re: twist rates and end results

Geland,
I fire 110 and 130 grain bullets from my 3006 at 3150 for the 110 and 2992 for the 130. I have a standard 1:10 twist and these are lightly constructed bullets for use on varmints. The 158 grain bullets(Sierra 158 JHP .357 dia. for 38 and 357 through my 358 at velocities of just over 2700 fps. in a 12 twist instead of the 17 twist for pistols. Yet I have never had any of them blow up or not be able to find a sub-MOA group with them.

I expected the pistol bullets to explode because they are spinning more than 2.5 times as fast as they are supposed to. There has to be more to it than just spin rate.

gelandangan · Posted: Sun Dec 18, 2016 3:45 pm Post subject: Re: twist rates and end results

Paul I use cheaply made (bullet factory) 130 grains hollow point to play with my WHisper a few years back and damaged my Chrony when the projectile exploded. (there is a write up here somewhere about how I repair the machine).

Nowdays I use either Sierra or Hornady, more expensive but seems to hold out better, however nowadays I rarely load beyond 2200 fps anyway.
2200 fps seems to give me best accuracy with the WHisper.

Elvis · Posted: Sun Dec 18, 2016 6:46 pm Post subject: Re: twist rates and end results

paul....gel has faster twist than that so his rifle will be delivering more spin even at slower speed.your .358 pills terminal preformance was??????? explosive????? and the sierra 110 .308 pills are DESIGNED to be used at magnum velocities......
there are a few guys over here using the nosler ballistic tip 125 grn at supersonic speed in whispers with good results..... thats another pill I use in the x39mm with good results....its reasonably thick rear jacket will be helping to cope with forces applied to it.

slimjim · Posted: Mon Dec 19, 2016 5:39 pm Post subject: Re: twist rates and end results

Well, it will take me a wee bit of time to write my response to this one. I have tested twist rate on terminal performance and it can make a difference depending on the bullet. More to come. Lights out here.

Elvis · Posted: Mon Dec 19, 2016 9:01 pm Post subject: Re: twist rates and end results

cheers Mate...knew you would have the low down n dirty on this one somewhere Very Happy