For what it's worth, RE the feeding from the mag issues:
I have a pair of Chilean 1912/61 (IIRC) Mauser 98s which have been factory converted
to 7.62 NATO, reportedly with cut down surplus '03 Springfield barrels. Both feed fine
from the magazine, no probs. They were originally 7x57 and the "/61" is the conversion
in 1961 to 7.62 NATO. One is a four groove and one is a six groove barrel, makes me
think of High Standard's six groove '03 bbls and the normal pre-03A3 four groove barrels.
The six groove is a particularly good shooter, with ordinary Portugese surplus ammo it will
reliably put 5 shots into a group you can cover with your hand at 200 yds, 100% stock, with
all the ineffectiveness of the sights and stock triggers that this implies.
Bill