Save your money. - Adams Arms Standard Picatinny Block Piston Kit

Just another gimmick part. You will jump through hoops to find obscure pieces that fit and it doesnt cycle. Bought a pistol and rifle length. Neither are reliable. Tried various combinations of common barrels and buffer springs. Not worth the dollars, effort or aggrivation. Support other than a few videos online has been non-existant. Don't expect any kind of reply from Adams.