Thanks Guys!!!!.

Me too have wondered about these"humps" on the breech..but I too had a suspicion it might had something with a transition period of some kind. This rifle was for sale for over 2 years at LARKINS but no movement at all...and everytime I was looking at GI I really wanted this rifle. I guess my name was written all over this gun here.
Watson577 here on this forum has been very kind to share a few loads from his own personal experiences from a similar calibered rifle. Ballistic wise we are looking at a 475grain bullet at
1875 ft/sec as a regulating max load. EleyBros. loaded this special cartridge with a 480grain solid....where most other loads are found with a 440grain express bullet.
The serie# is 12354. Larking had the ledger on this gun so it would be interesting to get some history on this rifle too. I will defintly keep you all updated. Thanks for showing interest.