Chrome-Moly Steel

Chrome-moly steel, the family that includes the common 4140 and 4150 grades, alloys ordinary carbon steel with chromium and molybdenum for added strength and toughness. It machines and forges well and stands up to the heat and pressure of repeated firing, which is why it has long been a staple for both factory and some match barrels. The chromium content here is for mechanical properties, not corrosion resistance.

Because chrome-moly will rust if left bare, the outside almost always wears a protective layer such as bluing or a modern coating, and many barrels get a hardening nitride finish inside and out. Shooters often choose it for durability and value, while those chasing the cleanest finish and the easiest upkeep frequently turn to a stainless steel barrel instead.