Algodoo

To reload, duplicate the blue block next to magazin
and open/close the hatch with "Enter" (Numpad)

To stretch/release the bolt hold "+" (Numpad)

To ajust the speed of fire just set the rpm of the gear to whatever you like (do not go too wild)

You also could build a ramp in the floor next to the light brown block, to let them fly

Have Fun