A system for connecting an accessory to a firearm having an enlarged muzzle portion has a body with a bore sized to closely receive the enlarged portion. The body has a stop to limit the insertion depth of the muzzle. A gate is received by the body for movement along the path perpendicular to the bore axis. The gate has a recessed area sized to receive the enlarged muzzle portion. A spring generates axial force to retain the muzzle portion within the recessed area. Compression of the spring enables movement of the gate to shift between an open and closed position, so that the accessory may be removed or installed when in the open position, and secured when in the closed position.