Ballistics information needed

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Epesiarch

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I'm doing some work for a friend about recoil, and I need to get very mathematical and specific about it. Projectile energy is expressed in foot-pounds by the ammo manufacturers, but as far as I recall from my moderately extensive physics education, foot-pounds are normally a measure of torque, not energy. Can anyone help me out with the basic mathematics and science for ballistics, including metric conversions, or point me to a source?
 
e = mass x velocity (squared) or mvv

Projectile weight is weight (lbs force), not mass (lbs mass), so a conversion is required.

e = weight x vel x vel / 2 g, where g = acceleration of gravity or
32.2 ft/sec(squared)

now e = weight (lbs force) x vel (fps) x vel (fps) / 64.4 fpsxs

for a 180 grain bullet at 2700 fps:

w = 180/7000 = .026 lbs(f)

e = .026 x 2700 x 2700 / 64.4 = 2910 ft lbs(m)
 
45crittergitter,

Thanks for responding, but I am confused. I agree that:

E = mass x velocity, and metrically this would be kg m^2/s^2, or kilogram meters-squared per seconds-squared.

So when you say:

e = .026 x 2700 x 2700 / 64.4 = 2910 ft lbs(m)

how can .026 lbs x 2700 ft/s x 2700 ft/s divided by 64.4 ft^2/s^2 end up as foot-pounds? The ft^2/s^2 of the numerator will cancel the ft^2/s^2 of the denominator and we are left with only lbs. No feet.

So how and why are bullet energies expressed in a torque measure; and how can one even get to ft-lbs using the proper energy equation?

This is what has confused me the most.
 
Foot-pounds are indeed a measure of torque: force (in pounds) at a moment arm (in feet). But, the foot-pound is also a measure of energy or work in the English system. A ft-lb can be directly converted to the erg (cgs system) or joule (SI system).

Your error is found in the required accel of gravity units. You have squared the ft as well as the seconds. As 45crittergitter correctly stated, g = 32.2 ft per (sec squared), not (ft per sec) squared, but it may have been confusing in the manner it was shown.
 
Mal,

Any chance you know of any links describing this? When I google anything physics related I get innundated with tons of scientific papers instead of the basics that I want.
 
I'll see if I can find something ... hold on
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First of all, here's a good ballistic calculator: http://www.handloads.com/calc/
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still searching
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I can't find anything specific enough for the basics of the subject although I'm sure it's out there somewhere. I've found that if you Google for a definition in the form "define:energy", you'll usually get some good specific results. Try that.
 
FedGunner, if you're a ballistic technician, are there any resources you could point to? The equation that csmkersh's link goes to

E = 1/2 (Wr / 32) (Wb x MV + 4700 x Wp / 7000 x Wr)squared

is missing all the neccesary grouping brackets, such as is it:

E = 1/2 (Wr / 32) (Wb x (MV + 4700) x Wp / 7000 x Wr)squared

or

E = 1/2 (Wr / 32) (Wb x MV + (4700 x Wp / 7000) x Wr)squared

or any other number of possibilites.

What I really need to know is the math behind the recoil so that I can reproduce it with other devices to test recoil pad construction.
 
Wow, you're right. That formula is confusing and appears to be incorrect. In essence, it is the universal E = 1/2 MV^2, but they fail to convert the weight of the bullet to pounds like they did with the powder. The V is the calculated velocity of the rifle during recoil.

Here is a good discussion on recoil from Remington: http://www.remington.com/magazine/current/2004_0102.asp (Ignore the reference to the theory of relativity, Newton would not be amused. ;) )
 
What in the world made me think I could understand this thread? I need a drink!:D OR, go back to college. Maybe a major University this time!!!
 
Guys... no way I'm going to tackle that equation!

We use computers for that sort of thing.

Hell my head hurt just looking at it!
 
Too confusing for me.Mountain Man terms is .....Lots of footpounds does great job on large game :D
 
There are more than one formulae for recoil..... depends on whether you are looking for energy, velocity, momentum....

"I used to not be able to spell engineer, and now I are one."
 
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