August,
A little more info on the proof marks, 1924 German commercial proof laws changed and in addition to Crown over B (rifle proofed in assembled form), Crown over U(final inspection proof), sporting arms were stamped with a Crown over G (indicating a weapon with a rifled bbl). The BUG proofs were applied from 1924-1934, a fourth mark, Crown over N was applied from 1933-34 to late 1939 (to signify the rifle was proofed with nitro-based powder, Crown N was also used on military contract guns for export.)
The BGN marks on your rifle look washed out from being polished, with a distinct Crown over U. Maybe it was reblued at the Mauser factory ?
Your barrel does not snap on/off its most likely the scope is removeable with quick detatchable mounts.
Bob
