The U.S. Army has agreed to hold another competition to replace the aging (nearly 30 years old) M4 carbine. There has been a lot of pressure from the troops and Congress (where many of the complaints end up, after all, the M4 users are also voters). The basic infantry weapon, the M16, is half a century old and the M4 is a shortened version of that. The rifle the M16 replaced (the M14) lasted less than a decade and the one before that (the M-1) lasted two decades. The one before that (M1903) lasted three decades and so on, back to the Civil War (1861-65). The M-4 is a variant of the M-16 that was adopted in the 1980s, but there are still plenty of M-16s in service.
Meanwhile, the army began upgrading its M4 assault rifles two years ago. Ultimately, upgrade kits will be purchased for 70 percent of the army’s half million M4 carbines and that turns them into M4A1s. The kits replace the barrel, receiver, and auto-loading system with one that is easier to keep clean. There is also a heavier barrel and the ability to fire full automatic. There are also stronger rails on top of the barrel, for mounting scopes and such. It will take until the end of the decade to complete this upgrade, which is currently being delayed by lawsuits from the manufacturer who lost out in the bidding competition to produce the kits. Such lawsuits by losing bidders are increasingly common in American defense procurement.
Most elements (except for the piston loading system) were already incorporated by SOCOM (Special Operations Command) for their own M4s, which were the first M4A1 models to enter service. The marines are not upgrading their M4s (which are mainly used by support troops).
This conversion kit addressed years of complaints about the M4 and M16 assault rifles. The main change was replacing the main portion of the rifle with a new component that contains a short stroke piston gas system (to reduce buildup of carbon inside the rifle) and a heavier (by 142 gr/five ounces) barrel (which reduces barrel failure from too much heat, which happens when several hundred rounds are fired within a few minutes).
Much of this goes back to the decades old argument about replacing the recoil system in the M16 assault rifles, to make them more reliable and easier to clean. This came to a head (again) six years ago, when the army ran more tests on its M4 rifle, involving dust and reliability. Four weapons were tested: the M4, the XM8, SCAR (Special Operations Forces Combat Assault Rifle), and the H&K 416 (similar to the new M4 with the upgrade kit).
The testing consisted of exposing the weapons to 25 hours of heavy dust conditions over two months. During that testing period, 6,000 rounds were fired from each of ten weapons of each type. The weapons with the fewest failures (usually jams) were rated highest. Thus, the XM8 finished first, SCAR second, 416 third, and M4 last. In response, the army said it was satisfied with the M4's performance but was considering equipping it with a heavier barrel (to lessen overheating) and more effective magazines (27 percent of the M4s 882 jams were magazine related). The army noted that the M4 fired over 98 percent of its rounds without problems. That missed the point that the other rifles had far fewer jams. In combat each jam is a life threatening situation for the soldier in question. The army had been forced by Congress to conduct the tests. Congress was responding to complaints by the troops.
The XM8 had 127 jams, the SCAR 226, and the 416 had 233. Thus the M-4 had nearly eight times as many jams as the XM8, the rifle designed to replace it. The M4 had nearly four times the jams of the SCAR and 416, which were basically M4 type rifles with a different gas handling system. Any stoppage is potentially fatal for the soldier holding the rifle, thus the disagreement between the army brass and the troops who use the weapons in combat.
In dusty places like Iraq and Afghanistan you have to clean your M16 and M4 rifles constantly, otherwise the combination of carbon (from the recoil system) and dust in the chamber will cause jams. The army and marines both decided to stick with their current weapons, rather than adopt an easier to maintain weapon, like the XM8 or H&K 416, because of the billion or so dollars it would cost to switch rifles.
If the issue were put to a vote the troops would vote for a rifle using a short-stroke system (like the XM8, SCAR, or H&K 416). But the military is not a democracy, so the troops spend a lot of time cleaning their weapons and hoping for the best. The debate involves two intertwined attitudes among senior army commanders. First, they don't want the hassle, and possible embarrassment, of switching to a new rifle that might have even more difficult problems. Second, they are anticipating a breakthrough in weapons technology that will make possible a much improved infantry weapon. This is likely to happen later, rather than sooner, but the generals kept obsessing over it. They are encouraged by recent success in development of caseless and short case ammo for a new machine-gun design.
Earlier efforts to just get the troops a more reliable rifle have failed. Back in 2005, the U.S. Army's design for a new assault rifle, the XM8, was cancelled. But now the manufacturer has incorporated one of the key components of the XM8 into M4 rifles and calls the hybrid the H&K 416. Heckler & Koch (H&K) designed the XM8, which was based on an earlier H&K rifle, the G36. SOCOM is using the 416 but no one else is (except for a few police departments).
The XM8 (like the G36 and 416) uses a short-stroke piston system. The M16 uses the gas-tube system, which leads to carbon build up and jams (rounds getting stuck in the chamber and the weapon unable to fire). The short-stroke system also does not expose parts of the rifle to extremely hot gases (which wears out components more quickly). As a result, rifles using the short-stroke system, rather than the gas-tube, are more reliable, easier to maintain, and last longer.
H&K developed the 416, for SOCOM, at the same time the XM8 was being evaluated by the army. SOCOM got the first 416s in 2004, a year before the army cancelled the XM8. The 416 looks like the M4, for the only thing that has changed is the gas system that automatically extracts the cartridge after the bullet has been fired and loads the next round. SOCOM can buy pretty much whatever they want, the U.S. Army cannot. SOCOM listens to what its troops want, the army often doesn't.
The army made some other changes, as part of the M-4 component replacement. These included improved trigger pull characteristics, ambidextrous controls (to make life easier for lefties), and a round counter (in the pistol grip) to track the number of bullets fired over the lifetime of the rifle (makes for better data on how rifles perform over time and for scheduling the replacement of components).