Slug ft. lbs. of energy question

MikeS · January 28, 2002, 02:19 AM

I'm new to this area but am interested in the study of ballistics.

I recently read where the .50cal BMG cartridge with a bullet weight of 750gr. at 2,700 fps has a ft. lb. energy rating, at the
muzzle of 12,143.

My question is : Why is it that the Federal 10ga. 1.75oz slug at a
slightly larger 766gr. and with a fps at a little less than one half (1,280), rates only at 2,785 ft. lbs. of energy or less than one quarter of the .50BMG. Does 2X the speed equal 4X the impact?

I'd appreciate any clarification. Thanks.

Mike

Rottweiler · January 28, 2002, 05:08 AM

Let's haul out the ol'slide rule...

Bullet energy is calculated by the following equation:

KE=(Mx V^2 )/450400

where

KE= kinetic energy( in foot/ pounds of energy)
M=mass of the bullet (in grains)
V=Velocity of the bullet (in feet/ second)

As you can see a small change in the velocity will produce a much larger change in energy than a small change in the mass of the bullet.

I've found slight variations in the 450400 depending on who's book/website you get the formula from, but they are all close to that number.

After proofreading this post I realize that as I get older I'm starting to sound like one of my college physics professors. I gotta get away from the computer and get some trigger time

stick · January 28, 2002, 10:11 AM

You've got it Rottweiler. Kinetic energy increases as the square of velocity. So, doubling the velocity will yield a 4x increase in energy.

C.R.Sam · January 28, 2002, 11:27 AM

Speed Kills.
As stated, velocity² is the key.

Sam

MikeS · January 28, 2002, 03:00 PM

Rottweiler,

Thanks for your clarification on determining bullet energy.

I was confused because the only formula I had seen was the
Taylor Knockout Value use on the Garrett Cartridge and other
large bore manufacturers' sites: Bullet Weight x Bullet Diameter
x Max. Velocity/7000. The TKV apparently puts a premium on weight
rather than speed.

This formula has the 10 slug at a rating 0f 105. vs. 144. for the
50BMG. Of course, the 50cal still retains 2.5 tons of impact at
a 1000 meters (s).

Mike

January 28, 2002, 02:19 AM	#1
MikeS Member Join Date: April 17, 2000 Location: San Diego, CA USA Posts: 57	Slug ft. lbs. of energy question I'm new to this area but am interested in the study of ballistics. I recently read where the .50cal BMG cartridge with a bullet weight of 750gr. at 2,700 fps has a ft. lb. energy rating, at the muzzle of 12,143. My question is : Why is it that the Federal 10ga. 1.75oz slug at a slightly larger 766gr. and with a fps at a little less than one half (1,280), rates only at 2,785 ft. lbs. of energy or less than one quarter of the .50BMG. Does 2X the speed equal 4X the impact? I'd appreciate any clarification. Thanks. Mike

January 28, 2002, 05:08 AM	#2
Rottweiler Senior Member Join Date: January 30, 2001 Location: Texas Hill Country Posts: 391	Let's haul out the ol'slide rule... Bullet energy is calculated by the following equation: KE=(Mx V^2 )/450400 where KE= kinetic energy( in foot/ pounds of energy) M=mass of the bullet (in grains) V=Velocity of the bullet (in feet/ second) As you can see a small change in the velocity will produce a much larger change in energy than a small change in the mass of the bullet. I've found slight variations in the 450400 depending on who's book/website you get the formula from, but they are all close to that number. After proofreading this post I realize that as I get older I'm starting to sound like one of my college physics professors. I gotta get away from the computer and get some trigger time __________________ Texas - envied by lesser states since 1845

January 28, 2002, 10:11 AM	#3
stick Member Join Date: September 6, 2001 Posts: 90	You've got it Rottweiler. Kinetic energy increases as the square of velocity. So, doubling the velocity will yield a 4x increase in energy.

January 28, 2002, 11:27 AM	#4
C.R.Sam Senior Member Join Date: October 29, 1999 Location: Dewey, AZ Posts: 12,858	Speed Kills. As stated, velocity² is the key. Sam

January 28, 2002, 03:00 PM	#5
MikeS Member Join Date: April 17, 2000 Location: San Diego, CA USA Posts: 57	Rottweiler, Thanks for your clarification on determining bullet energy. I was confused because the only formula I had seen was the Taylor Knockout Value use on the Garrett Cartridge and other large bore manufacturers' sites: Bullet Weight x Bullet Diameter x Max. Velocity/7000. The TKV apparently puts a premium on weight rather than speed. This formula has the 10 slug at a rating 0f 105. vs. 144. for the 50BMG. Of course, the 50cal still retains 2.5 tons of impact at a 1000 meters (s). Mike