Question , What do you consider to be a P-88 bore ? It would not chamber an original German military S round ? Is the chamber clean ? Some of my civilian barreled rifles will not chamber a S but will chamber a military P . That problem also showed up on some of the SA Czech barreled Gew-88's with their civilian spec barrels . If it is in 8.15 x 46 mm it could not chamber a P round . Now it does sound as if it is a " custom " order for civilian ammo . I am not well versed on just what could be ordered by civilians in Pre WWI Germany , any help there ?