Just trying to figure out who made the Upper. It has the same "keyhole" marking on the upper, but those were just the markings on the barrel. That would be awesome if it was a Bushmaster. I'd feel bad for the guy I traded though. He went from a Bushmaster 16" Upper, to a Model 1 Sales 11.5" Upper!
Without wanting to appear a smartass (which I sometimes am) use Google on your 'puter. There is a wealth of information available.
From Wikipedia:
Magnetic particle inspection processes are non-destructive methods for the detection of surface and sub-surface defects in ferrous materials. They make use of an externally applied magnetic field or electric current through the material, and the principle that the magnetic flux will leave the part at the area of the flaw.
Well I'd seen some info on the process but not for the barrel. i didn't know if there was something different about how they do the barrel versus, say, a piston cylider or something.
I'd looked it up, just too much info to sift through and none of it pertained to AR barrels. I just got a bunch of tech pages about **** above my pay grade! LOL
Shooter, I appreciate your help. I know, I'm ignant. I've seen the keyhole stamp on just about every upper I've held besides the Colt uppers. Figured maybe it was just a normal thing!
Actually I have an 11.5" BCM barrel right now and it's perfect. Just long enough to provide clearance for mounting my suppressor while using the DD RISII rail. The complete package is just under 16" and I have no problem with accuracy at MOM sized targets at what I'd call average distances- 300m. I won't be shooting anyone farther away than that