Re: Springfield 03-A3 never fired?
The FJA (Frank J. Atwood) mark, the circled P behind the trigger guard, the symbols ahead of the magazine floorplate and the barrel markings (plus the crossed cannons mark, if it can be seen) are original. The 3-GMK indicates a postwar cleaning and refurbishment, if not a rebuild.
So the gun has not only been fired it has been issued and used enough that it was refurbed.
AFAIK, no one has ever found out definitively who/what "3-GMK" stands for. There have been all kinds of guesses, but I don't recall anything official. The most common idea is that "GM" stands for General Motors, with the "K" indicating a plant, or maybe a government inspector. As I say, all guesswork.