the animation is okay, drawings need work but still looking pretty decent, I like that style.
BUT ! You could have made this sooooo much more enjoyable just by adding a few frames in the beginning, when hes like aiming and then, at the very end you could have made him put the arm back in the aiming position and overshoot as hes going down, then up and down again and try to match your last and your first frame, so it looks like a loop.
Something like this,
http://filebox.me/view/fn4xuxw7a , I made it in like 10 minutes but you can see what Im aiming for, right ?