Our model MB is the same bolt and port length as the model B but has an integral sleeve that goes over .935 inch of barrel, this is to allow more bedding surface. This action is 8.500” long and has several exterior shape options. Starting weight is 38.5 oz and varies with options chosen. Load port length is 3.00 inches and barrel tenon is 1.062 x 18 tpi. Max barrel is 1.25 inch with max shoulder contact of 1.23 inch.