Patent ID: 7013592

Claim:
A gas-operated automatic or semi-automatic gun comprising a barrel having a breech section defined by a breech peripheral surface plus a muzzle section defined by a muzzle peripheral surface, said breech section having a longitudinal portion of said breech peripheral surface encircled with an array of concave depressions each defined by a depression opening, selected from circular openings and oblong openings, of predetermined area in said breech peripheral surface and of predetermined maximum depth, said longitudinal portion having a first peripheral surface area A 1 before inclusion of said concave depressions and the combined surface areas of said concave depressions and the remaining surface area of said first peripheral surface area after inclusion of said concave depressions having a second peripheral surface area A 2 , and the ratio A 2 /A 1 is between about 1.17 and 1.42.