IBM Barrel Marking

[painter777]

I have an IBM M1 carbine, receiver #3665xxx with an IBM barrel marked IBM Corp 8-43.

I was cleaning around the gas piston and noticed a small heart shaped proof mark directly under and in front of the piston. I never saw that before and can't find an example in the limited carbine library I have.

Can anyone shed light on this mark?

Thanks.

I may have found one in a GB auction.
IBM barrel dated 9-43
Serial# 3,672,211

A link to the auction.... (Again 2 links so one will work)
Excellent condition IBM M1 carbine : Curios and Relics at GunBroker.com

Excellent condition IBM M1 carbine : Curios and Relics at GunBroker.com


I also copied off a picture.
Is this the marking you have?
OH... BTW... I have no idea what it means

HTH,
Charlie-painter777