Simulation of shock on the shoulder when the gun fired

Hello everybody,

I've a question, Which kind of boundary conditions is required for simulating shock on a shoulder when a gun fired?

I'm going to test some conditions, for example: test one gun is without damper, test two gun has a damper.

I wanna figure out the different between these conditions. And understand the effects of the damper on reducing the stress on the shoulder.

Best Regards