[Slater]

http://www.armalite.com/library/techNotes/tnote48.htm

Haven't heard many complaints lately. Have these issues been resolved?

[3rdpig]

The one test I saw, it's posted over at arfcom, shows catastrophic barrel failure on the M4 after 530 rounds of sustained full auto fire, all rounds were fired in under 3 minutes. Once the barrel reaches about 1500 degrees it blows out. Supposedly the M16 barrel actually fails even quicker, I say "supposedly" because I haven't seen those tests.

The average soldier doesn't carry eighteen 30 round mags. The M4 is not a SAW and was not designed to be one. Almost every air cooled barrel will overheat and fail with sustained full auto fire.

Funny thing though, Colt developed and is the sole provider of M4's, and one of their main competitors, Armalite, produces this paper on M4 unreliability. Kinda of like Ford releasing a report of Chevy unreliability. You've got to take it with a grain of salt.

[Slater]

http://stinet.dtic.mil/cgi-bin/fulcrum_main.pl?database=ft_u2&searchid=0&keyfieldvalue=ADA317929&filename=%2Ffulcrum%2Fdata%2FTR_fulltext%2Fdoc%2FADA317929.pdf

I think that this has been posted before, but evidently the M4's barrel is at least reasonably durable.

[jeff-10]

I have seen SAW barrels warp from too much sustained fire too quickly. SO obviously any barrel can warp or be damaged from too much heat. After all its only metal.

[Risasi]

Spraying is for deadheads. Come on, get a heavier barrel if you are a hoser...

[Bartholomew Roberts]

A carbine length gas system will cycle harder and faster than a rifle length gas system. The M4 uses all the same components as a rifle designed around the 20" barrel, so it will be harder on those components.

Most of the issues mentioned in that tech note are valid; but are generally not seen until you start pushing the envelope by adding suppressors, lots of full auto fire, suppressors with full auto, etc.

There are any number of fixes that address these issues (which aren't very common to begin with). I've even seen people go overboard and apply so many "reliability enhancements" to cycle slower/reduce pressure that they had a very fancy straight pull bolt action when using anything less than NATO ammo.

Most carbine length gas systems are very reliable from the factory without modification. A cheap way to increase your odds without risking any malfunction is to upgrade the extractor spring. Another no-risk solution is Magpul self-levelling followers and new springs for all the magazines used with that rifle.

Beyond that, there are many specific approaches to reducing the cyclic rate and pressure in the carbine length gas system that can be used alone or together depending on how much reduction is needed and what the criteria are... these include heavy buffers, extra power buffer springs, fatboy gas tubes, pigtail gas tube, enhanced bolt carriers with with extra dwell time, and I'm sure even more options.

In my opinion, it is a bad idea to use those more specific approaches unless you have already identified a problem with a particular gun since you can also create malfunctions due to lack of pressure.