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.
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.
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
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'?
In the beginning God created the heavens and the earth. Genesis 1:1
"And can the liberties of a nation be thought secure when we have removed their only firm basis, a conviction in the minds of the people that these liberties are the gift of God?" Thomas Jefferson - Notes on the State of Virginia
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.