There's a known ser# range of both LCS and Fulton Hunter Special shotguns that most all of the US Ordnance marked guns fall into.
The LCS collectors seem to have the total number of the LCS guns narrowed down to a certain #. I'm not certain about the Fultons.
These have the Flaming Bomb Ordance mark on the bbl(s) or bbl flats.
as well as the MArks of the Rochester (NY) Ordnance Depot and the Chief Inspector assigned there at the time.
FWIW, That Building is now a live Stage performance theater)
There's another marking that shows up,,'USA-F'.
But the marking doesn't also have the Ordnance Bomb marking with it nor the Roch Ordnance Depot marks.
If you search over on the LCS Forum,,there is some chatter on past threads about the markings, guns and history.
The L.C. Smith Collectors Association
Since the guns were purchased from Marlin Firearms at that time (owner of the LCS gun & mfg rights in 1942),,there are some records for the back and forth between the Ordnance Dept and Marlin.
FWIW, the Ordnance marked LCS's do show up rather frequently at least in this area (WNY). Usually just Field grade extractor 12ga guns.
The Fultons, rarely.
They always draw interest and questions.
The LC Smiths purchased are often thought to be all of 12ga, but 16 and 20ga's have been found as well. Not all Field grades either. Some lower Graded guns too and with Ejectors, ect.
Seems the LCS warehouse pulled and delivered what ever was available
Some recollections of Servicemen from the era state that they trained for aerial gunnery using a SxS shotgun as well as the Pump and semiautos.
Shooting from the back of moving flat bed trucks,,shooting on Trap and Skeet fields was common.
Getting a knowledge of lead and follow through was key.