montana Wrote:Does anyone know if these new weapons have nitride or chrome lined barrels??
SIG already uses nitrided barrel in their 716 series from which the "Spear" was developed. There have been some reports that they use "maraging" steel, a high strength alloy for some of their components (bolt, feed ramps), but I can't verify it it is used in the barrel. Maraging steel is extremely tough stuff. The tail hooks of naval aircraft use it, for example.
As for the barrel bore coating or treatment, I suspect nitriding for the rifle but maybe chrome for the machinegun. This is based on an interview on Forgotten Weapons with a representative from Faxon, a company that makes both nitrided and chrome lined barrels. He stated that the existing SIG 716 uses nitriding to increase barrel life and corrosion resistance. The Faxon rep stated that nitro-carburizing (nitriding, meloniting) is better for many weapons, but chrome is still better for machineguns. He said that it had to do with the fact that chrome has better high temperature properties than nitrocarburized steel. Nitriding diffuses nitrogen and carbon into the surface layer of existing steel. This makes the surface harder but does not change its thickness. With a chrome-lined barrel, layer of chrome is applied on top of the steel and is chemically bonded to it. This makes the surface of the barrel bore a composite structure. During long bursts, the steel making up the barrel gets hot enough to anneal (soften) and according to the Faxon guy, and the rifling on a nitrtocarburized barrel "begins to fade" whereas the rifling on a chrome lined barrel does not. (Note: Faxon makes button-rifled barrels and he did not mention if the problem was as severe with cut-rifling barrels). I have included a link about the acceptance of nitriding and when chrome lining is still preferred. The Faxon guy talks more about nitriding earlier in the video, if that is of any interest to you.
https://youtu.be/e2X1iaQbjg8?t=426