New to me Colt M1917

[Lee Enfield]

The extraneous markings "1" is likely a fitter marking. Colt worked on a piece work system and if there was a problem with an individual gun it was traceable to the fitter, who fixed it on his own time.

I suspect "G" is a coded marking referring to the US government - sort of a contract marking.

The marking above the serial and on the cylinder is the eagle inspection marking.

Most of the .455 guns will have an "E" which is believed to refer to "England" or "English".

Other stamped markings may have referred to the forging dies used, or a specific material.

Also as discussed the fact that it's parkerized indicates that it has been refinished or possibly rebuilt - usually that would be stamped with coded markings to indicate who/when/why ect.