Original M1A1 carnimes were made at Inland; serial numbers of
M1A1 production are mixed with serial numbers for M1 carbine
production at Inland. During arsenal rebuild, a lot of M1A1 and
M1 carnines were given M2 stocks as standard replacement,
but the M1A1 stock hung around as a non-std replacement.
Basically, there is no M1A1 carbine: there is an M1 carbine in an
M1A1 stock; original production M1A1 were Inland (General Motors).
Especially in early days of VietNam, M1A1 stocks were altered
to clear the selector switch for the M2 carbine. Some of these
"M2A1"s had a front sight welded or soldered to the barrel
band, and the barrel then bobbed to about 12".
My repro Italian M1A1 stock is inlet for the M2 selector switch.
Local dealer has an original Inland carbine with original M1A1
stock; the big difference between repro and original are the
sharp edges on the repro wood and perfect bluing. A fake
would be easy: correct era Inland carbine ( L sight, push button
safety, no bayo lug) careful aging and patina on stock wood
and metal, viola, caveat emptor!