Possibly R.F. Sedgley, Philadelphia Pa. Inc. Made custom rifles in the early 1900's, but also made 10Ga hand held flare guns for the military in WWII, some known 10Ga shotgun flare pistols were made in 1942 and 1943. If these were the actual flare headstamps, someone would have shot some off testing or just for whatever, as I assume most of these would have been fired overseas, but it's possible he made shotgun shell of the same Gauge.
Flare shells came both in headstamp type ammo as well as non-headstamp(basically a long casing.)
A long shot, maybe some other info else will turn up