Before the surge of troops in Afghaninstan, the U.S. Army was considering an new model of carbine to replace the M4 used today (and variants for several other kinds of small arms used by infantry). The new design, called the XM-8, promised to weigh a little less than its predecessor, easier for non-infantry like truck drivers to use in close quarters, and most importantly, to be significantly less prone to jamming when receiving heavy use in dusty environments.
The primary opposition to the change came from soldiers who feel that the NATO standard 5.56mm round used by the M4 and M16 is too small, and should be replaced by a larger 6.8mm round, and from defense contractors who weren't happy with the bidding process. A process had been in place to pick a replacement, but it crashed and burned after several name changes, with upgrades to the existing M4 design looking likely to prevail. While the program would have an immense impact on the daily life of soldiers, changing the primary weapon of hundreds of thousands of them, the program wasn't very expensive, because the technology involved is not revolutionary and small arms aren't expensive compared to vehicles and other major weapons systems. (Subsequently, there were changes made to ammunition, basically favoring a version of hollow point bullets, but the size has been maintained. Also, far more troops have shifted from the full sized M16 to the M4.)
Now, a draft lessons learned report on a recent U.S. battle in Wanat, Afghanistan that went badly says that one of the factors in the battle's bad outcome was that a lot of U.S. M4's jammed during the long firefight. While the battle was small, it was one of the bigger defeats the U.S. has suffered in Afghanistan.
When the battle in the small village of Wanat ended, nine U.S. Soldiers lay dead and 27 more were wounded. A detailed study of the attack by a military historian found that weapons failed repeatedly at a "critical moment" during the firefight on July 13, 2008, putting the outnumbered American troops at risk of being overrun by nearly 200 insurgents.Alternatives to the M4 have performed much better in terms of jamming risk.
This wasn't the only problem, or even the only procurement related problem. The unit there was also short on purified water, because U.S. troops in Afghanistan have only rudimentary water purification equipment.
This isn't to say that procurement was the only, or even the primary problem that the report identifies. But, it strikes a nerve because the military procurement problem is very prone to making big ticket investments in programs like new attack submarines, destroyers and fighter jets, while not focusing enough attention on lower budget, incremental improvements in the basic tools of the trade, like carbines and water supply systems, that get heavy use and may have a greater impact on U.S. troop casualties.
While military outsiders were not in agreement over which alternative to an M4 was best, and agreed that the Vietnam era M4 was a good design for its time that had provided long and decent service, almost nobody participating in the discussion said that the last few decades had not produced any possible replacements for the M4 that were better than what our troops were using by our troops.