My first Enfield!

[jmoore]

A doubly scarce rifle being both peddled scheme and 1950's FTR with the Suncorite finish.

The "U" bolt head shows up on all sorts of rifles. I reckon (until corrected otherwise) it is an "U"nfitted replacement bolt head. (It would now be fitted to your rifle, but the "U" is rather too deep to remove, so there it stays.) I think I still have one or two that never were fit, and they are too long to work in any rifle encountered to date.

The "G" is the serial number prefix.