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Physically measuring forces of gun recoil

  1. Dec 22, 2014 #1
    I want to measure the forc
    e of an AR15 recoiling over time from a single shot. The gun cycles at about 900 rpm, so the recoil impulses should be over within 67 miliseconds.

    There are two different parts to the recoil impulse. Within less than a milisecond, there should be a large impulse that represents the bullet and gasses exiting the barrel. Just as that is happening, the gasses should be hitting the bolt carrier group and they should be traveling rearward but slowly applying more recoil force. About 33 miliseconds in, there may be a spike in recoil as the whole bolt carrier group impacts the rear of the receiver extension tube it's traveling in, and then it should have negative forece moving the other way under pressure of the spring and finally there should be a negative force as the bolt carrier group slams shut.

    Any ideas what I would need to buy to measure these forces in time?
    Is there a cheap way to just measure the peak force?
    My brother said his coworkers at an IT company put padding on a hammer and used some app that weighs things or measures g-forces and they would take whacks at it with a hammer and it would tell them how hard they hit kind of like those high striker hammer games at carnivals. Anybody know anything about something like that?

    Here's a video example of something one guy did to measure the Newtons of a shotgun blast. What is that equipment he's using?
     
  2. jcsd
  3. Dec 22, 2014 #2

    Bystander

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    A strain gauge and an oscilloscope. Finding a suitable "shoulder" to mount the strain gauge for the scale of force you'd be looking at is the problem, probably something like axial loading of a piece of 1 1/4 inch brass sink drain.
    Set the butt against a piece of 2 x 4 sitting against the top of an empty aluminum soft drink can --- see if you can get any deformation.
    It would be easier if you weren't dealing with quite such a pipsqueak cartridge as is used in the "15."
     
  4. Dec 31, 2014 #3
    use a piston and cylinder filled with water to be forced through a pressure gauge. piston attached to the stock and the cylinder to a solid mount similar to the video set up. this should give you a pretty accurate recoil force measure.
     
  5. Dec 31, 2014 #4

    Doug Huffman

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    Just like in physics class, a pendulum and a marker for its extreme position.
     
  6. Jan 4, 2015 #5
    Probably late, but whatever .... It may be possible to use an old smartphone accelerometer to estimate the peak force by attaching the phone to the side of the gun .... or buy an expensive accel.
     
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