ok, first of all, are you using onion skinning? his body is moving around like crazy. you should fix that.
i see that you included a bit of anticipation before he fired his gun, which is good, but the recoil is a bit too slow. on top of that, the projectile moves too slow to make the recoil (and that the guy tied to a tree is blown away) appear natural.
the projectile should continue in the same direction, it looks a bit like it hits an invicible wall at the end.
i hope this helps, i find it a bit hard to explain things properly so just send me a PM if you don't understand what the hell i'm on about, and i'll try to help you further.