Bayonet type coupling for firearms

A bayonet type coupling to removably coaxially attach accessories to a gun barrel wherein the gun barrel includes an end, an end region, an exterior surface and a radially extending lug defined on the end region axially spaced from the end having a forward edge facing the barrel end and a rear edge facing away from the barrel end, an accessory adapter having an axis, accessory mounting means, an axial bore, an inner barrel receiving end, a lug receiving opening defined in the adapter inner end, and a lug retaining recess defined in the adapter bore retaining the lug upon insertion of the lug within the opening and rotating the adapter and barrel relative to each other about the adapter axis, the improvement comprising, a sleeve within the adapter bore axially displaceable between first and second positions, a bore with said sleeve receiving the gun barrel end and end region upon being inserted into the adapter opening, an abutment defined upon said sleeve engaging the lug forward edge upon insertion of the barrel end region into the sleeve bore to displace said sleeve from said first position to said second position, and a spring biasing said sleeve toward said first position, said sleeve retaining the lug within the adapter lug retaining recess under the force of said spring.