1. The XM21 was a heavy barrel match M-14 rifle built by Rock Island Arsenal for the military. They originally build about 1,400 of them for use in Vietnam. In 1971, it became the M21, and was the primary US Army sniper rifle until 1988.
The M-21 did not have a heavy barrel. It was only an M-14 that exhibited better than usual accuracy over other M-14's and was then selected to become an M-21. The selector was removed and a scope mounted. A cammed Redfield scope was mounted on the one I had. If I recall correctly the cammed scope permited accurate fire between 300 and 600 meters.
