I have Meffert No.21231. It's a two barrel set - 16x16 and 16x10.15 Serbian. The rifle barrel is marked 67/49. I load for it using .43 Mauser brass, 300 grain .429 bullets sized down to .423 with a full case of Pyrodex or 2F. Prints right to the sights.
Note: All my Mefferts have a serial number on their metal butt plate.