If possible we should sticky this thread.

Now with the threads melonite over chrome lined M-4 barrels, I feel we should see what's what. So I found this US Army post.

The U.S. Army reported the Mean-Time-Between-Failures (MTBF) for M16A2/M4/M4A1 barrels is 9600 rounds. These are chrome lined barrels with a 1:7 twist made out of 4150 steel (just like Bushmaster & Colt use), and they see full-auto use. Also note the military is using full power M193 & M855 rounds, while most commercial .223 runs 100 to 200 fps slower (with the same bullet weight). The 1:7 twist barrels do burn out quicker than the 1:9, especially under full auto stresses. For a chrome lined barrel on a semi-auto only rifle 20,000 rounds (or more) can be expected. [Warning: More civilian barrels are ruined to over (or careless) cleaning than to being "shot out".] Stainless barrels won't last as long, 4140 steel barrels wear longer than stainless; but not as long as the Colt 4150 barrels (w/o the chrome lined bores). nor as long as the chrome lined bores (given the same shooting)."