Goal here to add the sensation of recoil to a prop rifle gun.  I have seen it done with compressed air and motor pistons, but neither are easily synchronized with electronics and capable of rapid firings for full auto fire.  Leaves me with the third option of using a solenoid.  To fire a solenoid with enough furiosity to kick the gun into your shoulder involves some serious power requirements. I did a dry run yesterday and came up with this circuit.  The solenoid is rated 12-24V and 3 lbs force.  Using the circuit below it was weak at 18V, fully actuated at 27V, and actually had some kick at 36V. …