Michael Eichele
Well-Known Member
Depends on the depth of the animal. Are you talking coyotes or moose?
Bullet Spin and Performance
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Depends on the depth of the animal. Are you talking coyotes or moose?
L
Lightvarmint
Guest
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.
Fiftydriver
Official LRH Sponsor
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.
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.
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.
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.
Michael Eichele
Well-Known Member
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.
Michael Eichele
Well-Known Member
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.
Michael Eichele
Well-Known Member
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.
royinidaho
Well-Known Member
nteresting but I don't know what I'm seeing?
YouTube - Bullet in Flight Slow-Mo Video
Nor do I know what I'm seeing Here:
Do I see "threading" of the gelatin due to intial expansion, i.e., the drill in the hand thought?
YouTube - Hollow Point Bullet Through Gelatin in Super Slow-Mo
YouTube - Bullet in Flight Slow-Mo Video
Nor do I know what I'm seeing Here:
Do I see "threading" of the gelatin due to intial expansion, i.e., the drill in the hand thought?
YouTube - Hollow Point Bullet Through Gelatin in Super Slow-Mo
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davewilson
Well-Known Member
someone earlier said a 10 twist will produce 2 revolutions in a 20" wide animal. at close ranges this would be true but at longer ranges, if the impact velocity is half what it started at, the amount of revolutions would be much closer to 4. the "twist rate" of the bullet actually increases with the range because the rate of spin slows much slower than the velocity.
i know of a couple very experienced long range hunters that will not put anything on their guns unless it's an 8 twist barrel. reason being they simply get much better terminal performance from the faster twists. i'm not going to say it's a trend here in Pa. but it's certainly becoming more of an excepted concept.
most bullets used for long range hunting are much like varmint bullets. other than the Accubond, the bullets most preferred, Sierra, Berger, A-Max, are thin jackets. i wouldn't call them heavy jackets by any means. long range hunting is like varmint hunting but the impact velocities are 1/2 - 1/3 what varmint bullets are. most everyone i know wants fragmentation of the bullet for a larger wound channel. now i realize that we're shooting everything from coyotes to moose and this creates variables in bullet selection, but, for the most part, people want the bullet to fragment.
yes, i think the faster twists help.
i know of a couple very experienced long range hunters that will not put anything on their guns unless it's an 8 twist barrel. reason being they simply get much better terminal performance from the faster twists. i'm not going to say it's a trend here in Pa. but it's certainly becoming more of an excepted concept.
most bullets used for long range hunting are much like varmint bullets. other than the Accubond, the bullets most preferred, Sierra, Berger, A-Max, are thin jackets. i wouldn't call them heavy jackets by any means. long range hunting is like varmint hunting but the impact velocities are 1/2 - 1/3 what varmint bullets are. most everyone i know wants fragmentation of the bullet for a larger wound channel. now i realize that we're shooting everything from coyotes to moose and this creates variables in bullet selection, but, for the most part, people want the bullet to fragment.
yes, i think the faster twists help.
L
Lightvarmint
Guest
Roy,
Thanks for posting the links of those videos..........
What was the twist of the barrel it was shot from and what was the bullet speed? The reason I am asking is because the bullet was in "yaw" when it penetrated the paper target..... The hole is substantially oblong in shape along the "y" axis (vertical). Additionally, it appears that the boat tail even cut a portion of the hole and it is not even part of the major bullet diameter.
If you look close, you can see the paper rotating as it tears away from center of the bullet while it is opening to allow the projectile through. When I shoot bullets out of the 1-8" twist at say 3400 fps, you can see the evidence that the land marks on the bullet actually torque and wrinkle the plastic as it goes through..... We do not see it with 1-10" twist barrels.
The eight cutting spirals in the gelatin are a great catch, thanks for verifying what we theorized about. You have taken the "theory" to the level of theorem and rule of thumb. Thanks a lot for the support. You are the hero of the day.
James
RockyMtnMT
Official LRH Sponsor
The 1.5 stabilization factor is the key. The problem that I have found is knowing weather or not you are there. How do you calculate it? It is highly variable based on the external ballistics of the projectile. Length mainly. The longer the bullet the more twist needed to get the 1.5 sf. Weather or not it groups doesn't tell you if the bullet is stabilized properly for hunting. The key is getting the base of the bullet entering the animal in line with the tip, causing the bullet to deform properly. You need the energy from the base of the bullet acting on the tip in a straight line to cause the bullet to deform uniformly and continue on in the intended path.
Correct me if I am wrong. I thought the permanent wound channel was caused by the shape of the deformed projectile. The more square the mushroom the larger the permanent wound channel. The more round in shape the mushroom is, the more "return to shape" of the temporary wound channel and the smaller the permanent wound channel. I thought that the spinning of the bullet was fairly easily stopped by the mass of the target. Once the bullet reached the target the job of spin was complete?
Thanks to every one involved here, I find terminal ballistics fascinating. Steve
Correct me if I am wrong. I thought the permanent wound channel was caused by the shape of the deformed projectile. The more square the mushroom the larger the permanent wound channel. The more round in shape the mushroom is, the more "return to shape" of the temporary wound channel and the smaller the permanent wound channel. I thought that the spinning of the bullet was fairly easily stopped by the mass of the target. Once the bullet reached the target the job of spin was complete?
Thanks to every one involved here, I find terminal ballistics fascinating. Steve
jmden
Well-Known Member
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.
Thank you for the graphic.
Would you please explain the concept of 'stability factor'?
MagMan
Well-Known Member
This is a doe I shot a couple of years ago from a 7mm RUM with a 30" 7 twist barrel at 75 yards. Bullet of choice were the 180 Bergers zipping out around 3300 fps (I'd have to find my book to know exactly, but I know its close). I also believe this to be the ragged edge of over spinning said bullets as some later down the line would dust immediately out of the barrel.
The doe was quartering to me at a downward angle with her head down. I aimed between the front of the onside shoulder and the center of the brisket approximately 4" below spine level (in the neck area). I don't have entrance hole pictures but from what I remember there was no bone contact (could be wrong though).
Not really sure where I was going with this but figured it was on par with the subject. Over twisted....yes, violent expansion....yes. In my eyes quite a winning combo. That combo counted for numerous kills that year with similar results all around, but trusting them to make it to their intended target was a game I'd rather not play.
The doe was quartering to me at a downward angle with her head down. I aimed between the front of the onside shoulder and the center of the brisket approximately 4" below spine level (in the neck area). I don't have entrance hole pictures but from what I remember there was no bone contact (could be wrong though).
Not really sure where I was going with this but figured it was on par with the subject. Over twisted....yes, violent expansion....yes. In my eyes quite a winning combo. That combo counted for numerous kills that year with similar results all around, but trusting them to make it to their intended target was a game I'd rather not play.
buffalorancher
Well-Known Member
The second video Roy posted visually puts things in perspective for me. The spin is definately easy to see. Thanks.
