Algodoo

lol, nice screenshot
this could be made to not jam by making sure that the part where the firing pin is is closed in by adding a little rectangle above the pin like this
....__|-|____
O--=_______

(ignore the dots (.))

see how the barrel also continues over top of the firing pin
if you dont understand just ask and i will make a demonstration scene

btw i didnt rate it down

well is was my first try at it anyway

i also made a gun just like that but it ejects the shell. i didn't put it here though coz it almost always jams