There are four basic aspects to using a gun in the anti-personnel role:

   You need to be able to hit what you need to hit, in order to elicit the desired response, as many times as you need to hit it, in order to elicit that response.
   You need to be able to get the gun into the fight soon enough to make a difference.
   You need to avoid shooting anyone or anything that is not doing anything that warrants shooting.
   You need to be composed enough to make good, appropriately correct decisions, in order to achieve 1,2, and 3...