Not for you Dick, this is for whomever.

In the beginning there were three positions at the Armory and there wasn't a clear delineation in who had what power:
Superintendent, Master Armorer, Ordnance Storekeeper.  Quite the little power plays early on.  The Superintendent was replaced by an Ordnance Officer eventually and the Ordnance Storekeeper was shuffled into his place - leaving the Superintendent with control.  As part of that the independence of the Master Armorer was eliminated but the position was still significant: the Master Armorer typically cartouched the guns.

Samuel W. Porter replaced Erskine S. Allin/Allen[1] as Master Armorer upon the latter's death.  SWP is the most seen trapdoor stamp and is also on early Krags.  With the death of Porter, as mentioned, stamping duties fell to Adams.  Adams worked through WW1 but his stamping duties were passed to others with the introduction of the M-1903.  As a result late Krags will be seen sporting other stamps (JFC comes to mind). 

Adams was still at SA when the "last Master Armorer" was appointed.  It wasn't Adams - it was Spooner.  Which I found odd as he wasn't senior either.

JSA is Adams of course - he stamped most Krags.  Not all but most.  As mentioned his stamping of guns didn't end with his death - he simply stopped doing it.

When the gun was "accepted" from production into the care of the Ordnance Storekeeper it became Army property - the stamp is an acceptance stamp.  While they're somewhat pointless on SA made items let's not forget that the stamps were also used in accepting contract made items.  WW2 Winchester made M1 Garands as an example.  M-1911 pistols.  Contact muskets.  The list is endless.  We should also not forget that SA wasn't under "Army control" when that practice was started - the Superintendent wasn't an Ordnance Officer.

[1] Not my problem the guy couldn't spell his name right.  Other branches of the family used the 'e' spelling.