A Sneak! Yep, they were built for *Special Purposes* by the Finns, who hadn't quite forgetten all the neat features of the M91 as reworked by Harry Manser. And your late M39 has the .311 bore and D-chamber that allows the use of USSR-/Warsaw Pact standard ammunition. My old 28-30s have .308 bores and use any good .308 bullet, usually a handloading proposition in the 7,62x53r case.