There seems to be a bug with the hit detection. Sometimes a bulls-eye would not actually register as a hit. Are there holes in the center of the targets? 

For a shooting range, the targets are quite un-engaging (flying straigth toward the player). Consider more interresting movement and spawn logic. 

Most players will not have headphones, so you ought to consider adding visual feedback to indicate what direction threats are approaching from. 

The muzzle flash looks quite poor and the gun sounds a bit too weak. Consider making your own assets or punching up the stuff you remix.