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RPM/engraving vs. Terminal Ballistics

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Unread 01-09-2004, 10:37 AM
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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.
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Unread 01-10-2004, 05:47 AM
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Join Date: Feb 2003
Location: Pueblo, CO
Posts: 1,245
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.
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Unread 01-10-2004, 08:36 AM
dwm dwm is offline
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Join Date: Feb 2003
Location: Texas
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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.

Something to think about.

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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Unread 01-11-2004, 12:57 AM
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Join Date: Jan 2003
Location: The rifle range, or archery range or behind the computer in Alaska
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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 ]
Long range shooting is a process that ends with a result. Once you start to focus on the result (how bad your last shot was, how big the group is going to be, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.
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