[QUOTE=Spiridonov]I mean chamber tapering inside of barrel (Like on Tannenberg handgonne). [/QUOTE.
I think this should be actually called a bore narrowing behind a bell-mouthed or widened muzzle.
I have often found this with a lot of 15th c. barrels when exactly measured, e.g. with my own famous haquebut barrel dated 1481, which you yourself handled in my collection. I think it was just an easy method to simplify loading the gun, especially with any kind of shot.
Please ref.: http://www.vikingsword.com/vb/showt...nich+dated+1481
Anyway, youre doubtlessly right concering the unusually thinness at the bronze muzzle walls - that's really astounding, especially for bronze! Seems to have worked in a way, though ...