You're right. The M1-A1 is the M1 Carbine with a metal folding stock. I'm pretty sure that it'd be under 16" with the stock folded, and therefore verboten without a class III stamp. I'm pretty sure he was talking about the M1A (civy version of the M-14).
D'oh! Got my dimensions wrong. The minimum length of a non-shotgun barrel is 16" under the NFA. The length of the barrel would, of course, be independent of the stock. The overall length must be at least 26" under the NFA.
All spec M1 Carbines are 35.5" in total length, and the folding stock on the M1A1 reduces that by about 10". That's still under the limit and makes a Class III stamp requried, presuming there is no prohibitive state law.
Phew.
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