[ToRN]

If I was responsible for implementing shield rules for a milsim/copsim game that I were organizing, I would probably do it this way:

1) any type of gun may be used with the shield, as a shotgun or rifle would most definately be more difficult when holding a shield in the other hand, thus negating any advantage gained by using a multiple shot/longer range weapon.

2) shield must be made of a material and thickness capable of being penetrated, but not with too high probability. [for example: 4 layers of cardboard glued together] since in the real world, ballistic shields are not bullet 'proof' but bullet 'resistant'.

and that's pretty much it.

Nic