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Bullet Spin and Performance

 
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  #15  
Old 12-21-2008, 03:46 PM
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Re: Bullet Spin and Performance

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Originally Posted by buffalorancher View Post
This all good info. and I really appreciate it. How much would a bullet spin in an animal if you were using a 1:10 twist? I can see where spinning in a drill would illustrate some spin but if a bullet only turns maybe twice while in an animal this wouldn't be an accurate representation of what it does to an animal, would it? I envision this as a cork screw from hell instead of a spinning mushroom of death.
Depends on the depth of the animal. Are you talking coyotes or moose?
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  #16  
Old 12-21-2008, 03:59 PM
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Re: Bullet Spin and Performance

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Originally Posted by buffalorancher View Post
This all good info. and I really appreciate it. How much would a bullet spin in an animal if you were using a 1:10 twist? I can see where spinning in a drill would illustrate some spin but if a bullet only turns maybe twice while in an animal this wouldn't be an accurate representation of what it does to an animal, would it? I envision this as a cork screw from hell instead of a spinning mushroom of death.
BR,

One turn will cut your hand, two turns will cut your hand more and then three turns will make you wonder why you even let it happen in the first place.

Lightvarmint.
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  #17  
Old 12-21-2008, 04:45 PM
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Re: Bullet Spin and Performance

In my opinion, if your using a big game bullet or any bullet using a relatively heavy jacket, RPM levels really will have no effect on penetration or expansion as long as they are not high enough to cause bullet failure in flight. If that happens, there will be no penetration or expansion in the intended target anyway!!!

I have tested this quite a bit, no scientic testing, just what we all can do. In my opinion, If the bullet will survive the launch velocity and RPM levels at the muzzle, down range effects will be nearly identical.

The only thing I have seen is that bullets seem to penetrate in a slightly straighter line when they are fired from a faster twist barrel. This is espeically true when dealing with long solids or bullets that when expanded still have a relatively long bullet length after expansion. Bullets that expand to the point that they are less then 50% of their original length, they seem to penetrate pretty darn straight.

There is one area of shooting and hunting where rpm levels can make a dramatic difference in expansion. Varmint hunting. Here we are taking bullets with very thin jackets and driving them as fast as we can. I have tested on several occasions with two 22-250 rifles, one in 1-14 twist, the other in 1-9. Shooting several different bullets. With conventional bullets that would handle the rpm levels in the faster twist barrel, those bullets produced noticably more "POP" on game such as gophers, prairie dogs, jack rabbits and rock chucks compared to the same bullet at same velocity in the 1-14 twist barrels.

I had to be careful to limit velocity to the same in both. Bullets such as the Speer TNT, Sierra Blitzking and Hornady V-Max had the occasional bust cloud if I pushed things to hard. The Ballistic Tips took anything I could throw at them in either barrel with ease.

I also found there was a more dramatic "pop" using tipped bullets in the fast twist barrels, again, driving them as fast as possible. With these situations, I believe these bullets are on the ragged edge before coming apart anyway, except perhaps the Ballistic Tip. When they impact, they literally come apart. Those that are tipped simply dust. Now some will say why are we seeing some exit wounds on larger varmints? Well, if you shoot a yote at 20 yards with 00 buckshot, you will likely see an exit wound.

Same idea here. Even though the bullet has fragmented violently, all the pieces are still in close proximity and still traveling at very high velocity. They shed velocity quickly and in game such as a coyote, most will not exit but on say a jack rabbit or rock chuck, most often even though the bullet has fraged darmatically, they still exit.

Again, in my opinion, for big game bullets, its hardly worth talking about at long range other then perhaps straight line penetration that may be improved with higher RPM levels.

Just my 2 cents.
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  #18  
Old 12-21-2008, 05:58 PM
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Re: Bullet Spin and Performance

I think the faster spin rates will produce more physical damage than the slower twist rates. But I don't shoot enough big game animals to ever prove it to myself, let alone others.

I doubt that the differences in bullet damage/destruction on a big game animal are substantial in fully loaded rounds with cartridges used for LRH. The bullet contruction itself is way more important than the rpms the bullet is spinning at, when loaded to full velocity - my opinion. I say this because the majority of bullets from LRH big game rifles are spinning within +/- 15% rpms. We're all sending them as fast as we safely can, while maintaining good accuracy. And the barrels commonly in use are 8-10 twist barrels. If someone's using a 6 twist or a 14 twist, maybe they'd see some obvious difference in bullet performance.

On the other hand, if we take a bullet that's normally launched at 3200 fps second and launch it at 1600 fps to replicate a 1000 yd velocity impact at 50 yds, then we've cut the rotational velocity by 50% and I wouldn't be surprised to see less damage at 50% less rpm spin rate. I could also believe the bullet may not expand/deform/perform identically at 1/2 the rpms while penetrating the animal, compared to a much higher rpm rate at the identical impact velocity.
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  #19  
Old 12-21-2008, 07:27 PM
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Re: Bullet Spin and Performance

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Originally Posted by Fiftydriver View Post
In my opinion, if your using a big game bullet or any bullet using a relatively heavy jacket, RPM levels really will have no effect on penetration or expansion as long as they are not high enough to cause bullet failure in flight. If that happens, there will be no penetration or expansion in the intended target anyway!!!

........

Again, in my opinion, for big game bullets, its hardly worth talking about at long range other then perhaps straight line penetration that may be improved with higher RPM levels.

Just my 2 cents.
Very well put, very true.
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  #20  
Old 12-21-2008, 07:34 PM
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Re: Bullet Spin and Performance

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Originally Posted by phorwath View Post
I think the faster spin rates will produce more physical damage than the slower twist rates. But I don't shoot enough big game animals to ever prove it to myself, let alone others.
You are correct. This "more physical damage" is caused by the extra cavitation inside the animal from the added rotational force. How much more will it help in killing power? It cant hurt but I personaly dont rely on it. I and most should rely on reliable expansion which will happen at the manufacturers recomended velocity levels regardless of over spinning or not. It is this expansion that is resposible for MOST of the "killing power". An animal can live quite some time after being hit with a FMJ regardless of the amount of cavitation caused by the bullet. The wound channel is still too dang small.

I for one would much rather spin a bullet at its 1.5 factor and have the max amount of BC and accuracy to get it to the animal in the first place.
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Long range shooting is a process that ends with a result. Once you start to focus on the result (how bad your last shot was, how big the group is going to be, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.
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  #21  
Old 12-21-2008, 07:57 PM
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Re: Bullet Spin and Performance

It just dawned on me that some of you may not know what this "temporary cavitation" I refer to is. See picture below. Most have seen pictures of tests into ballistc geletain. You see the wound channel straight through and sometimes fragments. But the cloud looking or bubble that you see in the middle is this cavitation. In game itis temporary because things (albiet are damaged) return to normal minus the actual wound channel. The greater the rotational forces, the greater this cavitation will be. Please note: I am not an advocate of overspinning. I am an advocate of higher BC's. Just relaying what happens and why.

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