I'm trying to identify a blackpowder double-barrel shotgun. The only markings I have found on it are the tiny initials "LT" stamped on the underside of each sideplate, and the serial number 1558 followed by a capital 'I' (the letter following H). The 'I' is at a slight spacing from the numbers. This number is stamped on the underside of each barrel and the underneath rib at the chamber end. I would guess the gauge at something like a 20-gauge. There are no gauge markings on the barrels. The stock is walnut and the barrels are not marked as to gauge. I know this isn't much to go on, but I would appreciate any information anyone would be able to provide. Thanks!