Custom service rifle builder
I have seen posts about military M21 receivers being re- marked, but in reality I have not seen any actual military receivers that had the markings changed. I handled several M21 rifles while shooting with the National Guard and none had the original M14NM markings changed. There were two different ways to mark the M21 receivers. One was to grind off the original marking and stamp or engrave a new marking. The other was to simply engrave M21 on the flat just behind the rear sight.