How about this?
OPEN
Rifle: power factor as listed now, any sights (including multiple setup, i.e. scope and dot), bipod, horse-drawn cart, etc
Shotgun: Any modifications (speed loader, big buttons/levers/etc.), any mag capacity, any sights/combination of sights
Pistol: as open
LIMITED
Rifle: power factor as now, no optics, no compensators beyond "as issued" birdcage flash hiders (that 1" by 3" rule seems to make sense, as it allowed the folks with M4geries to run with what they bought).
Shotgun: 9 rounds (in the gun) at any time, no speed loaders, no comps, no ports, no optics.
Pistol: Limited
Production:
Rifle: Oh boy, this is where my cleverness leaves me (and there wasn't much to start with). Power factor as above, "as issued" configuration, no external modifications beyond recoil pads, no optics.
Shotgun: Pump, no more than six rounds in the shotgun at any time, no external modifications from factory-issue except recoil pad (can you tell I'm a wimp?).
Pistol: as Production
While I'd like to see a "military" class for ACOGs and the like, I'm cruel enough to only allow the matching pistols and shotguns. An M4 carbine set up with an ACOG is workable, but an M9 and an Mossy 590 would be...interesting...next to a 15-round 1100 and an Open pistol :b
Alex