Originally Posted by
freefly
Duh, I knew that! It was an FN M16 BCG that I ended up putting in a Colt, hence the mix-up (post edited, sorry for the confusion). Not sure, but I am guessing that FN suppliers sold excess/over-runs/etc. with the proof mark ground off to remove any evidence that they were designated for FN, as to not get caught violating the Colt/FN non-compete agreement.
Bottom line for the OP is that if you see a carrier in the wild without any markings (ala LMT) or with the markings ground off (ala some FNs), it isn't an automatic red-flag that it's a sub-par BCG.