I saw a list on another forum called "Code Marking" which listed the US inspectors name and
marking of their inspection stamp.

I found a really bad error on the first inspection cartouche for the M1 rifle starting with serial
number 81 in Aug 1937. The inspector listed for the SA S.P.G. cartouche is Samuel P. Green ?

The actual inspector was Stanley Ployart Gibbs who started employment at Springfield Armory
in 1916 and became a small arms inspector during the early 1930's . His boxed SA S.P.G.
cartouche is found on M1903 rifles and on the first production of the gas trap M1 rifles starting
with serial number 81. Some 50,000 gas trap and 20,000 gas port rifles received the SA S.P.G.
cartouche (note the crossed cannon stamp was not used at this time).

Later after WW2 the SA S.P.G. rebuild stamp was used by Gibbs on rebuilt M1 rifles and Carbines
until 1951DSCN1559.jpgDSCN1556.jpgDSCN1557.jpg