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[eb in oregon]

"It's a ignorant ruling by an agency that can't critically reason.
Scrub the marking off and it's not an M2. Simple."

There's no advice. Read it again, what it actually says. If you don't get it that time, just move on.

Actually you did as you suggested that someone with an M2 receiver merely had to scrub that stamping off and voilà it's no longer an M2. That you don't think that's advice doesn't change that it actually is. And scrubbed or not stamping compresses metal and by the application of the proper procedure that M2 can be read and someone would go to jail or pay a mighty big fine. If you sir want to play games with the ATF have at it but making suggestions to others to do so is pretty poor thinking.