ft. lbs.: ballistics question
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Elder User
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From: Billings, MT
ft. lbs.: ballistics question
I understand the ft. lbs. concept just fine when it comes to engine twisting force, but I'm not as in the know when it comes to ballistics. For example: average 230gr .45ACP bullet @ 850 fps is 370 ft. lbs.
What does this mean exactly? I'm guessing it has nothing to do with twisting force.
What does this mean exactly? I'm guessing it has nothing to do with twisting force.
Post Fiend
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From: Montana Territory
Ft.Lbs measured is impact energy.
Its actually the number of pounds of force applied to a square foot of the target.
It takes around 750-800 to cause instant death in a deer, and around 1400 to cause instant death in an elk.
Check out http://www.shootersforum.com I hang out there, and so do a bunch of rel knowledgeable guys.
Its actually the number of pounds of force applied to a square foot of the target.
It takes around 750-800 to cause instant death in a deer, and around 1400 to cause instant death in an elk.
Check out http://www.shootersforum.com I hang out there, and so do a bunch of rel knowledgeable guys.
Posting Guru
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From: Florida Hill Country
Its a relationship of how fast the bullet is travelling and the actual weight of the bullet (projectile). The shape and trajectory have an indirect effect because they do affect the the bullets speed.
Other things to consider is the shape and bullet design, more specifically how does it behave once it hits the target. Those things will affect penetration. It doesn't necesarily transfer all of its energy on the target.
Other things to consider is the shape and bullet design, more specifically how does it behave once it hits the target. Those things will affect penetration. It doesn't necesarily transfer all of its energy on the target.
Post Fiend
Joined: Jan 2003
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From: Montana Territory
The only way to change the Ft.lbs of impact energy is to increase or decrease or to change powders.
I get my .257" bullets going 3400 feet per second (muzzle) and 2100 lb.ft at the target (ballistic gelatin).
I get my .257" bullets going 3400 feet per second (muzzle) and 2100 lb.ft at the target (ballistic gelatin).
Posting Guru
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From: Florida Hill Country
I disagree with you on that. A military full metal jacket on a 30-06 compared to a soft point will react different at the target. The first will pass through completely while the latter will mushroom causing it too make a bigger whole and allowing the more of the energy to be transferred to the target. Its kind of like HP of an engine and how much actually makes it to the rear.
Another example is the classice .45 acp with a 230 grain hardball compared to a hollow point.
Decrease/increase in powder charge changse the speed of the projectile. Bullet Weight and speed determine the potential at the target. The farther away from the target the slower the bullet when it gets there.
Another example is the classice .45 acp with a 230 grain hardball compared to a hollow point.
Decrease/increase in powder charge changse the speed of the projectile. Bullet Weight and speed determine the potential at the target. The farther away from the target the slower the bullet when it gets there.
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From: Billings, MT
I know all the ft. lbs. calculations and how to get all those numbers, I was just wondering what it meant.
Just as it means force in pounds one foot from the axis in engines, I was curious as to how to explain it in layman's terms.
The explanation of 370 pounds of force on a square foot implies that it's simply a matter of pounds per square inch, expressed in a different way.
Thanks, folks.
Just as it means force in pounds one foot from the axis in engines, I was curious as to how to explain it in layman's terms.
The explanation of 370 pounds of force on a square foot implies that it's simply a matter of pounds per square inch, expressed in a different way.
Thanks, folks.
Posting Guru
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From: Florida Hill Country
Its basically a measure of energy like the engines torque. Broncozilla hangs out at a board that discusses stuff like this.
I think he has a different name on that board.
When the bullet is in the air, it is potential energy.
I think he has a different name on that board.
When the bullet is in the air, it is potential energy.
Last edited by rlh; Feb 4, 2004 at 02:07 AM.
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Posting Guru
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From: mesa, az
...Not sure if its relevent,
Back in the old days they measured ballistic energy with a pendulum of a known wieght...measure the distance the pendulum swung when struck with a projectile, then throw some physics formula and they came of with the ft/lbs energy number. The old Lyman's reloading manual (circa 1980's) has an excellent chapter on this exact subject.
Back in the old days they measured ballistic energy with a pendulum of a known wieght...measure the distance the pendulum swung when struck with a projectile, then throw some physics formula and they came of with the ft/lbs energy number. The old Lyman's reloading manual (circa 1980's) has an excellent chapter on this exact subject.
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Post Fiend
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From: Eastern WA
Energy is also work which is force X distance, thus it is expressed in ft-lb. For example, potential energy is mass X gravitational accel X distance. Torque is rotational energy due to a force being applied to a lever arm, thus the units of ft-lb (or in-lb).
As was correctly noted above, the ballistic pendulum can be used to determine the energy of a bullet upon impact. A block of known mass is suspended in air and is impacted by a bullet of known mass. The fired bullet has kinetic energy due to it's mass and velocity; when it penetrates and joins the suspended block it causes the block/bullet combo to swing in an arc, changing the postion of both. The kinetic energy becomes potential energy as the two masses move to a new position and come to rest. By knowing the distances traveled and the mass of the bullet and suspended block, you can determine the energy of the bullet (in ft-lbs) at the time of impact
As was correctly noted above, the ballistic pendulum can be used to determine the energy of a bullet upon impact. A block of known mass is suspended in air and is impacted by a bullet of known mass. The fired bullet has kinetic energy due to it's mass and velocity; when it penetrates and joins the suspended block it causes the block/bullet combo to swing in an arc, changing the postion of both. The kinetic energy becomes potential energy as the two masses move to a new position and come to rest. By knowing the distances traveled and the mass of the bullet and suspended block, you can determine the energy of the bullet (in ft-lbs) at the time of impact
Last edited by CowboyBilly9Mile; Feb 4, 2004 at 12:36 PM.
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