just got a muzzle gage from duff

[goo]

all my garands, o3's and 308 2a1 ishapore are fine.
the only carbine i have eats the whole gage.

[P. Greaney]

Mine measured at "3" on the gauge.
I could be wrong, but if I recall correctly, the M1 Carbine bore is .305 vice
.308 for the other ".30" caliber barrels you mentioned.
So, I guess that means that your barrel is considerably worn .