Twist rate vs killing power.

[jb6.5]

Ok, been kicking this around for a wile. My theory is with the same cal. Same bullet the faster the spin the more killing power you have. If the bullet continues to rotate threw the animal seems that the more rotations the more damage. My creedmoor has a 1-8 twist. The damage this little gun does is crazy. My 7 mag don't tare stuff up like this thing. Ive compared lots of bullets and damage on hogs to see what bullet does what. Just seems this would make a difference. Shot a hog last night with my cm using 129 gr interbond, thinking the bonded bullet staying together would mess up less meat. I put a 1/2 gallon bleach jug all the way through the hog when I pulled the hide down, don't seem typical for a bonded bullet. What do y'all think?

[stomp442]

I think that's awesome and wouldn't change a thing. 6.5s are great killers way over looked and under appreciated for the larger 7s and 30s.

[JackinSD]

Ok, been kicking this around for a wile. My theory is with the same cal. Same bullet the faster the spin the more killing power you have. If the bullet continues to rotate threw the animal seems that the more rotations the more damage. My creedmoor has a 1-8 twist. The damage this little gun does is crazy. My 7 mag don't tare stuff up like this thing. Ive compared lots of bullets and damage on hogs to see what bullet does what. Just seems this would make a difference. Shot a hog last night with my cm using 129 gr interbond, thinking the bonded bullet staying together would mess up less meat. I put a 1/2 gallon bleach jug all the way through the hog when I pulled the hide down, don't seem typical for a bonded bullet. What do y'all think?

So you are saying that a 1-8 twist bullet would have more killing power than a 1-12 twist bullet? In other words, that shooting an animal that is 12" thick side to side, that a bullet that twists 1/2 a rotatation more has more killing power?

[jb6.5]

Just seems that way. Don't really know. High rpms tare stuff up.

[JackinSD]

High RPM = 1/2 of a rotation?

[Westcliffe01]

Maybe the longer, high BC bullets tumble after entering and that is what is responsible for the damage ? The 75gr 223 match bullets I use on coyote seem to do that. If the velocity is still high the bullet will tend to break up when it tumbles too, thats like a hand grenade. My experience with 95gr SST's from a 243 Win is that when I shot a coyote in the butt, the bullet did not exit. It did not even take one step. The second of the pair was a pass through, behind one front shoulder and out in front of the opposite side. Everything between those shoulders looked like it was run through a liquidizer. I now am using 95gr Bergers in my 243AI and will soon be loading 105s in the fireformed brass. I think any of these high BC bullets is devastating on smaller game animals. We can't hunt deer with a rifle in this part of the country so I can't tell you how that works...

[jb6.5]

Twist rate may not have anything to do with bullet performance, but it sure seems to.

[JackinSD]

Twist rate may not have anything to do with bullet performance, but it sure seems to.

Not on terminal performance. Unless you apply the exact opposite of what you have implied. A bullet already tumbling, because of not enough twist to stabilize. Of course, the accuracy of said bullet would be difficult at any extended range.

[Westcliffe01]

I think this is a simple downrange energy answer because of the inherently high BC bullets one is shooting from this cartridge. Now a 129gr interbond is not a high BC bullet in this caliber with a 0.485 BC. But then what do you shoot out of your 7mm Mag ? A 150gr bullet ?

Now a good bullet like a 140gr Amax has a BC of 0.585 or an SST 140gr with a BC of 0.52 are each better than the Interbond, but the interbond will be going a bit faster (initially) The plastic tip will help it open up too.

A Berger 140 gr Match Grade VLD Hunting has a BC of 0.612 and at longer ranges is going to carry more speed and energy.

If rotational speed was what mattered, perhaps a 40gr varmint bullet out a 22-250 should be the best at 4000fps ? It should be rotating real fast...

[TC260]

Just seems that way. Don't really know. High rpms tare stuff up.

I don't know either. Some people who's opinions I respect say it does. Others say it doesn't. I suspect the lack of a definitive answer amongst knowledgeable people means there's a lot more to the answer than just, it does or it doesn't.

When looking at a video like this, http://www.youtube.com/watch?v=9gp8xJZO0c4 there's so much tissue damage being done by cavitation, I have a hard time picturing how the bullet itself is spinning around in there tearing stuff up. It doesn't have that much rotational energy and a small surface area.

The other angle I've heard is that the centrifugal force helps the bullet expand more violently, which in turn would lead to more cavitation. If that's true, then that probably opens a can o' worms because the result would likely be different between a 22 cal high velocity frangible varmint bullet and a moderate velocity, heavy constructed big game bullet.

[squirrelsniper]

I've shot a lot of animals with a lot of different things, but I can't say I've ever seen twist rate make a difference. It all seems to depend on three factors; velocity at impact (not MV), the individual construction of the bullet, and the biggest variable of all is exactly what the bullet hits once it enters the animal.

I certainly can't say that rotational velocity doesn't play any part, but if it does, it seems to just get lost in the myriad of other factors.

[limige]

If rotational speed was what mattered, perhaps a 40gr varmint bullet out a 22-250 should be the best at 4000fps ? It should be rotating real fast...
WARNING GRAPHIC IMAGE!!!!

http://i41.photobucket.com/albums/e256/limige/general%20hunting/050211192023.jpg
You brought it up. Heres what a 40 gr 22-250 does. Ive killed many deer with mine. I do believe a high rpm bullet does more damage. I also own a creedmoor and it does quite well indeed with vld's

Now my 22-250 is a slower twist but attains high rpms with the high velocity. But yes i think the rpms is part of the equation but so is speed

[jb6.5]

Killed some hogs with my 22 250 with 55 gr bt didn't exit but when we pulled the hide down I put both fist through the hole to the off side ribs. Now we use the lil ttsx. Almost Always exits and kills the crap out of them. The rpms is what makes the barnes work so well. My opinion.

[JackinSD]

A little on the subject: http://www.longrangehunting.com/articles/conventional-wisdom-1.php

[Geo_Erudite]

There is a thing called angular velocity, which could explain what is going on. In simple terms it explains why the Earth spins faster at the Equator and slower at the North and South Poles.

[davemuzz]

I've shot a lot of animals with a lot of different things, but I can't say I've ever seen twist rate make a difference. It all seems to depend on three factors; velocity at impact (not MV), the individual construction of the bullet, and the biggest variable of all is exactly what the bullet hits once it enters the animal.

I certainly can't say that rotational velocity doesn't play any part, but if it does, it seems to just get lost in the myriad of other factors.

I agree with S-squared 100%. There is no harm in overstablization of a bullet. In other words, you can shoot....say a 40gr V-max in a .223 thru a 1-12 twist barrel, an 1-9 twist barrel, and a 1-7 twist barrel, and they will all do the same "damage" to a groundhog if hit in the same place at the same velocity.

But the spin on the bullet wouldn't make any difference to the damage on the 'hog.

Dave

[earl39]

I agree with S-squared 100%. There is no harm in overstablization of a bullet. In other words, you can shoot....say a 40gr V-max in a .223 thru a 1-12 twist barrel, an 1-9 twist barrel, and a 1-7 twist barrel, and they will all do the same "damage" to a groundhog if hit in the same place at the same velocity.

But the spin on the bullet wouldn't make any difference to the damage on the 'hog.

Dave

I also tend to agree. 1 turn in 12 is the same no matter what the speed of the bullet is. You can twist a bullet at 1 rpm or 1 million rpms and the bullet will still only be turning 1 revolution in 12 inches, the difference is forward speed.

[Geo_Erudite]

I've shot a lot of animals with a lot of different things, but I can't say I've ever seen twist rate make a difference. It all seems to depend on three factors; velocity at impact (not MV), the individual construction of the bullet, and the biggest variable of all is exactly what the bullet hits once it enters the animal.

I certainly can't say that rotational velocity doesn't play any part, but if it does, it seems to just get lost in the myriad of other factors.


I agree with S-squared 100%. There is no harm in overstablization of a bullet. In other words, you can shoot....say a 40gr V-max in a .223 thru a 1-12 twist barrel, an 1-9 twist barrel, and a 1-7 twist barrel, and they will all do the same "damage" to a groundhog if hit in the same place at the same velocity.

But the spin on the bullet wouldn't make any difference to the damage on the 'hog.

Dave

Dave, Squirrel, and Earl, the more I read on this subject the more I tend to think you are incorrect. Too often we think in 1 or 2 dimenstions, this includes ballistics, but the reality is the bullets we shoot and the game we hunt are 3 dimensional. We tend to solely focus on the point of impact, rightfully so, but then we limit our understanding to what is occuring every where else. To demonstrate:

1.) 243 Winchester (1:7 Berger Recommended twist) shooting a 115 grain bullet at 3,000 fps (linear velocity) has an angular velocity (spinning velocity) of 327 fps. Which translates to 27 ft/lb of energy on a given point on a bullet body. While a 243 Winchester (1:9.25 Savage Factory twist) shooting a 115 grain (yes I know in reality this bullet wouldn't stabilize in a 1:9.25 twist) bullet at 3,000 fps has an angular velocity of 248 fps. Which translates to 16 ft/lbs of energy on a given point on a bullet body. NOTE: A 2.25 inch twist variance gives you 11 lbs of energy difference for a given point on the same bullet and linear velocity.

2.) 6.5 Creedmoor (1:8 Berger Recommended and Savage Factory twist) shooting a 140 grain bullet at 2,800 fps has an angular velocity of 292 fps. Which translates to 26 ft/lbs of energy on a given point on a bullet body. While a 6.5 Creedmoor (1:9 Bartlein barrel optional twist) shooting a 140 grain bullet at 2,800 fps has an angular velocity of 260 fps. Which translates to 21 ft/lbs of energy on a given point on a bullet body. NOTE: A 1 inch twist variance give you 5 lbs of energy difference for a given point on the same bullet and linear velocity.

3.) 270 Winchester (1:10 Berger Recommended and Savage Factory twist) shooting a 130 grain bullet at 3200 fps has an angular velocity of 278 fps. Which translates to 22 ft/lbs of energy on a given point on a bullet body. While a 270 Winchester (1:11 Criterion Barrel twist) shooting a 130 grain bullet at 3200 fps has an angular velocity of 253 fps. Which translates to 18 ft/lbs of energy on a given point on a bullet body. NOTE: A 1 inch twist variance gives you 4 lbs of energy difference for a given point on the same bullet and linear velocity.

4.) 7mm Remington Magnum (1:10 Berger recommended twist) shooting a 168 grain bullet at 3000 fps has an angular velocity of 267 fps. Which translates to 27 ft/lbs of energy on a given point on a bullet body. While a 7mm Remington Magnum (1:9.5 Savage factory twist) shooting a 168 grain bullet at 3000 fps has an angular velocity of 281 fps. Which translates to 30 ft/lbs of energy on a given point on a bullet body. NOTE: Only a 1/2 inch twist variance gives you 3 lbs of energy difference for a given point on the same bullet and linear velocity.

5.) 308 Winchester (1:13 Berger recommended twist) shooting a 168 grain bullet at 2700 fps has an angular velocity of 201 fps. Which translates to 15 ft/lbs of energy on a given point on a bullet body. While a 308 Winchester (1:10 Savage factory twist) shooting a 168 grain bullet at 2700 fps has an angular velocity 261 fps. Which translates to 25 ft/lbs of energy on a given point on a bullet body. NOTE: A 3 inch twist variance gives you 10 lbs of energy difference for a given point on the same bullet and linear velocity.

Though these numbers seem minimal, you need to understand that this number only represents a given point on the bullet body from the ogive to the tail (beginning of the tail for boat tail bullets). This number does not represent the sum total energy across the entire surface of the bullet body. Again this is energy across a 3 dimensional surface (the x, y, and z axis in geometric terms)

The energy above is not measured or calculated by ballistic software. That is because this energy is transfered everywhere else but the point of impact. In essence this is "lost" or "missing" energy in terms of ballistic software output. The best way to visualize this is to think of the bullet as a piece of wood on a lathe. Now try to grab the piece of wood as it spins at a low speed and at a high speed (if you have a lathe, please don't do this or even attempt). What happens? They both mess you up, but the high speed grab really messes you up (instead of a dislocated arm at low speed, you now have a broken arm and muscle ripped off the bone at high speed)!

The data that I present to you is at muzzle angular velocities from a 26 inch barrel. I have yet to figure a way to calculate downrange angular velocities, which are more complex then regular linear velocities. So before you rip me a new one about the fact this only represents at muzzle angular velocities, take note of the quote below by Ruprecht Nennstiel (http://www.nennstiel-ruprecht.de/bullfly/faq.htm#header)(He wrote EBV4 Exterior Ballistic software and he is referenced by JBM in the develoment of their ballistic software):



Q: How fast does a bullet lose its spin velocity?
A:This question cannot be answered in general. As a rule, spin is much less reduced than velocity: An estimate for the M80 bullet (7.62 x 51 Nato) fired vertically up gives the following values:
-all of the velocity has been lost at the summit
-only approx. 36% of the angular velocity has been lost at the summit.

Sidenote: A 264 Winchester Magnum (1:8 twist) shooting a 140 grain bullet at 3200 fps has an angular velocity of 332 fps. Which translates to 34 ft/lb of energy on a given point on a bullet body. While a 264 Winchester Magnum (1:9 twist) shooting a 140 grain bullet at 3200 fps has an angular velocity of 295 fps. Which translates to 27 ft/lb of energy on a given point on a bullet body. I state this because the 264 Winchester Magnum is the only .264 caliber factory rifle without a 1:8 twist (i.e. 6.5 Creedmoor, 260 Remington, or 6.5-284).

[JackinSD]

Can you explain how you derived those figures for me?

[WuzYoungOnceToo]

Dave, Squirrel, and Earl, the more I read on this subject the more I tend to think you are incorrect. Too often we think in 1 or 2 dimenstions, this includes ballistics, but the reality is the bullets we shoot and the game we hunt are 3 dimensional. We tend to solely focus on the point of impact, rightfully so, but then we limit our understanding to what is occuring every where else. To demonstrate:

{Excellent discussion of angular velocity and KE snipped}

All true. However, in physics there truly is no free lunch. For any given projectile, a higher twist rate that diverts energy from the production of forward velocity to produce a higher angular velocity is going to result in a lower muzzle velocity, with a correspondingly lower velocity at the target. But I'm far too lazy to even attempt to figure out the real impact of all this on things like the projectile's momentum at impact, total KE at impact, etc.