G acceleration 1

[lesniowski]

If a bullet is shot out of a gun at an acceleration of 1000 g's is the acceleration 1000*32.2 ft/sec^2?

 

[CoryPad]

Yes, assuming g = 32.2 feet/s². Remember, this would be the initial acceleration due to the volume expansion of the propellent gas. Then, you have the acceleration due to gravity, which typically acts perpendicular to the initial acceleration and velocity vectors.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[MintJulep]

Very shortly after leaving the barrel there is no more force providing positive acceleration. The only remaining forces are drag and gravity.

 

[JStephen]

To say a bullet is shot out of a gun with an acceleration of 1000 g's is pretty well meaningless. The bullet is accelerated while IN the barrel and begins decelerating shortly after leaving he barrel. While in the barrel, the acceleration will vary along the length of the barrel. So at some point in time, perhaps the acceleration would be 1000 g's, but knowing that tidbit won't give you any velocities or trajectories. Knowing the average accleration in the barrel gives you some workable numbers, though.

Some quick approximate math:
Assume uniform acceleration = a
V=at+Vo
S=1/2at^2+Vot+So
Assuming Vo and So are zero:
S=0.5at^2
Substitute t=v/a, and S = 0.5a(v/a)^2 = 0.5v^2/a
or a = 0.5v^2/S
Say, for 38 special, you might get 750 fps out of a 4" barrel:
a = 0.5 x (750 fps)^2/(0.333 ft) = 844,000 ft/s^2 or 26,000 g's...and this is a low-powered round. (This is the average acceleration, assuming acceleration is uniform in the barrel.)

 

[IRstuff]

And, of course, it's actually not uniformly accelerating while in the barrel.

A 105mm M735 APFSDS round has a PEAK acceleration of around 45,000 g's, but it occurs around 2.6 ms after firing, while the round doesn't leave the barrel until around 6.6 ms after firing, at which point the acceleration is a mere 12,000 g's.



TTFN

 

[JStephen]

High-powered rifle rounds should run about 3-4 times the pressure of that 38-special round, so that acceleration could be that much higher- my point was that a 1000 g's was a low figure. I would assume maximum acceleration with either the shortest rifle bullet (.17 or .22 caliber) or saboted bullets.

 

[arto]

dA/dt = Jerk
Like "don't jerk the trigger?" ;-)

 

[lesniowski]

This was just an example to ask a question about units. I'm sorry if this made anyone ponder about what type gun or bullet. CoryPad answered my question. Thanks

 

[amorrison]

Sometimes JUST answering the question is a pretty boring proposition . . .

I am finding this extra information very intriguing.

Keep the good work guys!