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# RPM/engraving vs. Terminal Ballistics

#8
01-09-2004, 10:37 AM
 Posts: n/a
Re: RPM/engraving vs. Terminal Ballistics

The bullet looses rpm much slower than fps. At long range the bullet has lost a lot of forward speed but is spinning almost as fast as when it left the barrel. A 3000 fps 1/10 twist bullet will be a 1/5 twist down range when it drops to 1500 fps. I think that when a fragmenting bullet hits an animal the spinning of the bullet will send pieces of the bullet flying. A faster spinning bullet will make more internal mess than a slower spin.
#9
01-10-2004, 05:47 AM
 Platinum Member Join Date: Feb 2003 Location: Pueblo, CO Posts: 1,153
Re: RPM/engraving vs. Terminal Ballistics

No Tim-- i'm just trying to find a way to get better terminal ballistics from a lower veocity VLD bullet (AR-15). I'm not sure if there's ever been any research in this area.
I'm getting 3100 f.p.s. m.v. from a 70JLK VLD, and i'm trying to figure out what else, if anything, can be done to increase terminal ballistics, and at what range i need to draw the line for good terminal ballistcs.
#10
01-10-2004, 08:36 AM
 Gold Member Join Date: Feb 2003 Location: Texas Posts: 614
Re: RPM/engraving vs. Terminal Ballistics

You may want to consider that rotation contributes to the overal energy of a bullet. I hadn't really thought about that until reading this thread, but it is true.

So far every discussion on bullet energy has been focus on forward velocity, IE:

Energy (translational)= 1/2 * mass * velocity * velocity

Well rotation also provides enegry:

Energy (rotational) = 1/2 * I * w * w

where I = momentent of inertia and w = angular velocity

The total energy = E(translation) + E(rotation)

So a faster spinning bullet does indeed have more energy than a slower spinning bullet.

I am sure that when a bullet impacts and starts to deform that some of the rotational energy is converted to heat and contributes to the deformation and tissue damage.

Interesting that I have never seen this in anything that I have read on ballistics and energy.

I will provide references if anyone dislikes the equations I provided above. It is basic Vector Mechanics.
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doug
#11
01-11-2004, 12:57 AM
 Platinum Member Join Date: Jan 2003 Location: The rifle range, or archery range or behind the computer in Alaska Posts: 3,262
Re: RPM/engraving vs. Terminal Ballistics

dwm is right.

The rotation of a bullet also adds to the overall energy of the bullet, not just the forward motion.

On the other hand, you cant turn a 30-06 into a 300 ultra mag by turning the bullets faster.

Also, these exact topics and calculations are covered in "Understaning firearm ballistics" by Robert Rinker

[ 01-10-2004: Message edited by: meichele ]
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