[HorseSoldier]

I thought it had to do with the Marine Corps' institutional emphasis on marksmanship. The M16A4 has a longer effective range than the M4.

USMC mythology.

With an ACOG and good ammo (Mk 262) I know from personal experience that an M4A1 is a boringly reliable 600 meter gun, so it will do anything the M16A4 can do in the real world as well as the make believe world of the qual course.

It also has a nifty forward pistol grip and a flat-topped, picatinny compatible receiver for the mounting of optics.

That's no net gain versus the M4, though.

I've read a couple of accounts of the Marines' battles in Fallujah and I have yet to come across any complaints about the longer M16A2-A4 in CQB scenarios.

Marines I worked with were universally envious of our M4s and considered the '16 a liability for real combat and gunfighting. Most thought that the M16 gave them an edge on the USMC Table 1 qual course, but most also thought that did not have much to do with fighting with a gun.

Still, there must be something good about the M4 because practically all of the SOF over there use it (or the C8). When I watched the doc, Armadillo, I was surprised to see most of the Danish troops using it.

The Danes adopted the Canadian flavors of the AR to replace the G3, though don't remember the exact time frame for that.

It's probably cost prohibitive but why hasn't any major arms manufacturer successfully come up with an assault weapon with a interchangeable barrel/stock? Each soldier would be issued with two barrel/stock assemblies- one carbine-length for CQB and one full-length for open ground or whatever. It's got to be cheaper than buying a whole new system every 5-10 years or so.

I know a number of ODAs that went downrange with multiple AR uppers, usually a combo of 10.5-12" barrels on one hand and 18" on the other, which allowed tailoring weapons to mission.

The SCAR, Magpul/Bushmaster/Remington Masada/ACR, and a couple commercial variants of the AR all incorporate user-changeable barrels. The main issue is cost, with a secondary issue of most chains of command being too stupid to use properly use that capability. Give a line infantry battalion two barrels per rifle/carbine and you'll have several hundred guys hauling around a spare barrel in their ruck just in case higher decides they need it (along with the MOPP gear, protective mask, and other crap).

Kind of like body armor. Way too many units, when given a tailorable armor ensemble, just make everyone wear everything and waddle around like turtles. Nobody has the intestinal fortitude to risk their career on incurring casualties that might have been mitigated by deltoid protectors and side plates and armored toe caps for boots, so instead we give up maneuver and winning on the battlefield in favor of surviving . . . and letting the other guy live to fight another day, too.