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Artillery recoil (not homework - real world!)

  1. Feb 26, 2009 #1
    1. The problem statement, all variables and given/known data

    i have a 76mm tank gun (it's legal and registered w/ the feds in case you are wondering) and i am interested in firing blanks - but here it the problem: i want the gun to recoil like it does when firing live rounds.

    here is how the gun works: there is a long barrel (about 10' or so) and it is mounted on a set of shocks (like car shocks) that are on either side of it (see picture below.)

    ------ (oil/spring recoil piston)
    -------------------------------------- (barrel)
    ------ (oil/spring recoil piston)

    ^that is a picture of the gun and shocks.

    ok, so when a real round is fired out of it, the barrel pushes back ("recoil") and the shocks compress as the bullet comes out. in case anyone cares, the projectile is about 11 lbs or so and it is fired with about 3lbs of gun powder (actually, it's referred to as propellant, but it's technically just made of smokeless powder, just in a different format to make it burn slower.)

    so - back to the problem. if you don't have a bullet, but rather just an empty shell with gunpowder in it and you fire the gun, then all the 'energy' or force or whatever it's called just goes straight out of the barrel, and there is no recoil. when firing blanks, one typically uses about 1/2 lb of gun powder.

    my question is this: if i place a 'cap' over the front of the barrel with a very small hole in it, will this make it so a blank round will cause the gun to recoil on the shocks, or just create lots of pressure and blow out the cap? obviously i'd have to carefully experiment with the size of the hole in the cap - but principally, would this work?

    2. Relevant equations

    i have no idea. i'm not a physics person. i'm not even a student. i just need some help with this physics related problem.

    3. The attempt at a solution

    no solution attempted! i'm not excited about experimenting with this thing without at least having some advisement on how it should theoretically operate under this 'blank' setup.

    it seems like anyone with a good grasp of elementary newtonian physics would be able to answer this (clearly, i don't.) :smile:
  2. jcsd
  3. Feb 26, 2009 #2


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    Homework Helper

    Quite an interesting problem, Prefetch. Thank you for it.
    I never thought about recoil with blanks - just assumed it would be there, I guess.
    But now that I think about it, there would indeed be very little recoil. I have even witnessed the same with demo rockets consisting of a pop bottle filled with air. They don't do much unless you put some water in to act as reaction mass. The air pushes the water out - it has much more mass than the air so you get more momentum.
    Mass x velocity is what matters.

    Reducing the opening on the gun will increase the speed of the gases escaping so you could see perhaps a doubling of the recoil. But nothing like shooting a shell.
  4. Feb 27, 2009 #3
    delphi51 - thanks for the information. i re-posted into the main classical physics forum to get more details. thanks!
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