Barrel Linings

In terms of barrel linings typically seen on AR-15s, and for that matter, most rifles, the two most encountered are nitriding and chrome-lined, both of which make the barrel harder and more durable than steel alone.

Nitriding/Meloniting/Armorniting are gas nitrocarburizing processes that change the surface properties of the barrel itself– inside and out– while chrome lining adds a layer of metallic chromium material to the surface of the barrel’s interior and chamber.

Chrome lined barrels date to at least World War II, being common originally on military rifles due to its heat resistance properties, Nitriding et al. is a more modern process and is easier (and cheaper) to apply as well as having the side effect of protecting the entire barrel, including the exterior.

With that, don’t confuse chrome-moly or chrome-moly-vanadium (CMV) barrels– which are made from alloy steel that includes mixes of chromium-molybdenum and/or vanadium– with a carbon steel barrel that has been chrome lined.