Gustloff bcd 42 RC Mauser K98k

[2k05gt]

I did find this: avk is--- Ruhrstahl AG, Brackwede-Bielefeld. Hope this is correct.

Yes thats correct..

I wonder what the 77 means
avk 77 41 bys

avk = Ruhrstahl AG, Brackwede-Bielefel
77 = ??
41 = Year
bys = Ruhrstahl AG, Guss-stahlwerk, Witten