These are CO2 powered sound-flash Thunder B grenades from Valken Tactical. The grenade is Co2 powered and sets off a loud BOOM when they detonate. The core is re-usable but each use expends one shell and one 12g CO2 cartridge. These are very loud and give the user a definite tactical on the field, and especially in CQB environments. This package includes three shells and one core. The core is 100% compatible with all brands of Thunder B replacement shells.