Ambivalent Skeptic

November 1, 2010

Gun momentum

Filed under: Science — Clint1911 @ 10:14 pm

Momentum = Velocity X Mass

Mass = weight/gravity

Thus

Momentum = velocity X weight/gravity

or

ft/s X lb/gravity

but we measure bullets in grains. So:

lb=7000 grain

gr=grain

g=gram

kg=kilogram

And while I am at it:

one gram = 15.4324 grains

and

One mil=1/1000th of an inch or .001 inches

One mm=millimeter=.001 meters

1 mm = 39.37 mil

1 meter = 39.37 inches

And

Gravity=32.174 Ft

s^2

Back to the equation give us

ft X gr lb / 32.174 Ft

s 7000 gr s^2

Which is equivalent to:

ft X gr lb X 1 s*s

s 7000 gr 32.174 Ft

thus

ft X gr lb X 1 s*s

s 7000 gr 32.174 Ft

Thus the units are “lb-s.”

So velocity (in ft/s) times weight (in grains) divided by 225218.

Using a hot 30-06 load of 150 grains at 3000 ft/s gives

3000 X 150 lb X 1 s = 2 lb-s (rounded from 1.998…)

7000 32.174

Or you could take the power factor (IPSC) and divide by 225 and incorporate the lb-s unit.

150*3000/1000 = 450

450/225 = 2

thus 2 lb-s

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