FA is Frankford Arsenal, or armory. Can't remember which.
The 2 digits are the year.
All of that ammunition is corrosive primed. If you shoot it, you'll have to clean the bore, chamber, bolt, and magazine with hot soapy water to prevent rusting.
My experiences with older US military ammo is that even the old stuff is surprisingly reliable.
Some years ago I put 30 or so rounds of .30-40 Krag headstamped between 1902 and 1904 through a Krag carbine. Only 2 failed to fire.
I've yet to have a failure to fire with US ammunition loaded during WW II.
"The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza
Baby Jesus cries when the fat redneck doesn't have military-grade firepower.