"High RPM" and Killing Power

RCrosby

Reading another post I came across reference to high rpm contributing to the killing power of a bullet. How much of a factor can this be?
Just to keep the math simple; if a bullet leaves the muzzle at 3,000 fps and the twist is 1 in 12 inches, that would be 3000 rev. per second, which seems like a lot, but if the bullet hits a deer and travels through about a foot of flesh and bone, that's one revolution from start to finish. (Ignoring for the moment the fact that forward travel will slow more quickly than rotational speed. I think?)
It the bullet is zipping through something like a ground squirrel you'd think that far less than a full revolution would be involved.
So what's the deal? Is rpm a significant factor in killing power?
p.s. Ed, Now it's getting interesting.

sandwarrior

RCrosby,

The only studies I know of relating to spin is the stability the bullet is given. The more stable the less damage. This was apparent when the US Military Went to the original M855 (1-7" twist, 62 gr. bullet)ammunition. This ammo was more stable on impact than the M193 (1-12" twist 55 gr. bullet). The added stability, and properties added (original had a steel penetrator) caused the bullet to punch through. Whereas the M193 was known for going out of control almost immediately upon impact. Causing a lot of yaw and break-up. Which in turn caused a much larger wound channel(s).

What was good for bullet flight was bad for terminal performance. The rotational speed itself does almost no damage. Only how it stabilizes the bullet at impact.

Rocky Raab

One might argue that the rotational force helps expansion by "flinging" the edges of the mushroom outwards. But it's a fairly feeble argument.

Other than that, no.

mbsams

Pure "Hog Wash" - this is exactly how "old wives tales" get started.

JustC

the decreased stability of the old slow twists, caused the bullet to "yaw" (as Sandwarrior stated) when impacting. There was less resistance needed to throw the bullet off it's original trajectory, which in turn can cause a larger wound or one that changes directions inside the target.

This si where the old wives tale of the M16 bullets tumbling came from.

Does it exist,...yes, will you see an on target difference,..probably not.

elubsme

RC. 3,000 revolutions per second comes to 180,000 revolutions per minute. Hypothetically the bullet stops in a microsecond, 180,000 rpm's to zero in a flash. I have seen bullets disintegrate on their way to the target. Doing the math on a .223 with 7" twist and a velocity of 3,000 fps gives the bullet a rotational speed of 308,520 rpm's. Bullet spin, unlike velocity doesn't slow noticeably if at all before impact. Example: ever notice how long it takes a spinning wheel to stop without assistance? A bullet that loses its gyrostability is a loose cannon changing directions until it loses its momentum. Have you ever shot tracers in the dark? Occasionally it would appear that you were being shot at. Somewhere back in the science of ballistics someone must have done research on the subject of bullet spin & wound size. The study wouldn't take much. A pair of .223's, one smooth bored & one rifled. Any way, my opinion is that bullet revolution is a factor in expansion. The American Rifleman did a test on the Gyrojet gun when it came out. They showed a picture of a spent rocket that had impacted a steel plate. There were circular swirls on the flattened rocket nose. I have this magazine, put away of course. 3000,000 rpm's is a lot of energy, it has to be absorbed somehow. bring on the ballisticians! Ed

Rocky Raab

The rotation rate is easy to figure. Take 12 and divide by the twist rate, then multiply by the velocity. That gives you turns per second. Multiply by 60 to get RPM.

That's the limit of my math ability, so I can't calculate the centripetal force the bullet jacket has to withstand. But it can't be overmuch due to the very short radius (.112" in a .224" bullet).

rotarymetertec

Those talking about military bullets and mushrooming. Their FMJ there not going to mushroom. Some of the first M-16's had almost no twist to them so the bullet would tumble and not nessacary go straight through a person. This could cause more damage and a lot of the combat was close at range. All of them should be out of the system as all units should have at least the A-2 barrel, but did find one in the early 80's when we had the A-1 barrel. Noticed the cleaning rod wasn't twisting when cleaning it. As the shooter was complaining he was having trouble on the 300m targets.

Rocky Raab

I'll not try to dissuade rotarymetertec from his beliefs about the M-16. But I would advise the rest of us to not repeat such stories lest we be laughed at.