02-04-2012, 10:50 PM
The US Military did an extensive study in the 1950's I believe, and looked at nitrided barrels, exotic alloys, barrel liners, Nickel Boron chambers, and about every advancement in metallurgy that had been introduced up to that time. For full-auto use, it was determined that chrome-lining helped maintain the bore and rifling longer than others, when abusive levels of full-auto fire were conducted. The combination of shock force, heat, pressure, and friction seemed to be dealt with best by chrome-lined barrels, at least for barrels that could be reasonably mass-produced.
For civilian, non full auto use, even a 4140 CMV steel is plenty fine, especially when nitro-carburized (Melonite/nitrided). I have personally run two AR15's with 4140 CMV barrels past the 10,000 round mark, where they had finally degraded in accuracy so much, that they couldn't reliably place a round on a 12" steel plate at 100yds anymore, and were retired. One was from a JT upper, and the other a Rock River Arms mid-length 16" heavy. All my other barrels have been 4150 CMV chrome-lined, stainless, or Melonited 4140 CMV, and I like the Melonited ones so far, as I do the Chrome-lined for high-volume guns.
I saw a Bushmaster 4150 CMV chrome-lined barrel at one of the courses I ran with over 26,000 rounds through it, and the first 4"-5" of rifling were pretty much gone. Owner replaces ejector spring, extractor spring, and recoil spring at proper intervals, and lost 2 lugs during that course, and is still driving on with that barrel and a new bolt...which shoots well enough for close-range work.
For civilian, non full auto use, even a 4140 CMV steel is plenty fine, especially when nitro-carburized (Melonite/nitrided). I have personally run two AR15's with 4140 CMV barrels past the 10,000 round mark, where they had finally degraded in accuracy so much, that they couldn't reliably place a round on a 12" steel plate at 100yds anymore, and were retired. One was from a JT upper, and the other a Rock River Arms mid-length 16" heavy. All my other barrels have been 4150 CMV chrome-lined, stainless, or Melonited 4140 CMV, and I like the Melonited ones so far, as I do the Chrome-lined for high-volume guns.
I saw a Bushmaster 4150 CMV chrome-lined barrel at one of the courses I ran with over 26,000 rounds through it, and the first 4"-5" of rifling were pretty much gone. Owner replaces ejector spring, extractor spring, and recoil spring at proper intervals, and lost 2 lugs during that course, and is still driving on with that barrel and a new bolt...which shoots well enough for close-range work.