An apparatus for use in place of a round of percussion primed ammunition in a weapon includes a power supply and a switch. The switch is responsive to the mechanism in the weapon that fires the ammunition. Operation of the switch may enable the power supply to supply power to a replaceable cartridge. The cartridge may propel probes for delivering an incapacitating electrical charge from the power supply to the target. Another cartridge may include contacts to be applied without propellant to the target to stun the target. The apparatus may be inserted in the barrel of a weapon, for example, into the muzzle of a grenade launcher.