Me personally think its a weapons handling problem. Recoil, the noise, and the after effects of the above. We have a machine called the EST 2000. A virtual trainer that has pneumatic rifles, pistols, machine guns. Now although never a replacement to the real thing, I believe that it is a valuable tool to train the muscle memory of target RE-acquitsion, how to "handle" recoil, and a numerous other ways to better prepare soldiers to use live ammo, so you don't spend all day teaching some POG (or Infantry) to zero all day using tons of ammo that could other wise be used to do good training.

Virtual and sim training are good to use to get rid of the range-isms that will affect the value of live fire training.

Of course I also believe that shooting a bunch to get comfortable is also good for every soldier.