The clamshell action was made both in blitz and Anson and Deeley form, both forms seen infrequently today, so are somewhat rare, especially compared to other double rifle action forms seen today. Everything that sideclips will do, will be done better by the clamshell action. They are bolted by normal Purdey type underbolt and Greener type crossbolt, sometimes square bolt, rather than round. Prior to WWII, the Germans made many different "oddball" double rifle action types, generally seeking an improved lockup or bolting system. The Kerstan bolt, a double Greener crossbolt type, was used on both O/U as well as sxs, though considerably better looking on the O/U., making for a very strong bolting system.