350 FPS using 2.0 bb's is the absolute limit for any gun used in CQB mode. If your gun shoots 351 it is out. Any gun shooting over 320 FPS must be semi auto only. 320 FPS and under guns can shoot full auto, but your gun must not shoot more than 25 rounds per second (RPS).
In general, shotguns and green gas blow back pistols have a zero MED (minimum engagement distance). There are shotguns which shoot over 350, and these are not allowed in CQB games.
Grenades are allowed as long as they are non-pyrotechnic. Smoke grenades are generally not allowed, with exceptions based on the field and time of year.
Weapons not allowed in CQB games: 1) C02 pistols, 2) shotguns shooting over 350 FPS, 3) pyrotechnic devices of any kind, and 4) home-made devices and booby traps.