Need help. What am I looking at...IBM w/ Ser.# deeply and sharply cut into stock...

I collect WW2 pistols, but don't own any WW2 rifles, and don't have any collector knowledge or books about them at all.

Stopped at a pawn shop today-took a break from work. Pawn shop has typical "guns" sign, and have driven by this place about 200 times, always telling myself that I should stop. Never did, until today (Mon 4/23).

Looked at an M1icon Carbine, IBM, Ser#3883132, was rough, but didn't seem to have been abused, no rust, no pits. What caught my eye was that the shoulder stock had the same serial number cut deeply and sharply cut into it, numbers were about 5/8" tall, and also had some numbers and an "X" painted onto the butt plate . The gun did not have any significant bluing, had browned. It looked to be all there, except the rear sight had been drifted clean out, but was taped to the trigger guard in a small plastic bag.
They wanted $800 for the piece.

Can someone give me any collector info on this weapon, as to year of manufacture, meaning or significance of the Ser# on the stock, what marks etc. should I be looking for, and a ballpark figure as to value.

If necessary, I could go back and try to get some photos,
but would appreciate some feedback first.

Thanks
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