I received my .577 double rifle yesterday. Made by Gustav Richter Breslat. Lots of case color left, bores are great and locks up tight. Chamber cast shows a length of 1.35" bore slug = .585". a cut down .577 case with a little removed about 1/4" in front of the rim fits. The problem that I see is that the inside neck diameter is .595. Going to be hard to fit a bullet in there. The closest that I can find in Handloaders manual of cartridge conversions is a .58 Roberts. Used to convert percussion to centerfire. I don't understand the crown over V on the rib and the total lack of proof marks on the barrel flats.