A debate has been simmering for years in military circles (see, e.g., here and here and here (O.K., that one is about another feature, bayonets)) and in particular in the military blogosphere (of which I am a fringe, token liberal member). It reached a full boil when the Army was on the verge of adopting a new carbine and rifle (the XM-8), and then ebbed when the contract was cancelled for reasons of procedural missteps in the procurement process for the project.
Now, the Denver Post has finally caught on. The issue is bullet caliber. U.S. and NATO forces generally use 5.56mm rounds (i.e. .22 caliber) for their carbines and rifles (such as the M4 and M16). The Russian AK-47s and certain specialty troops (snipers with M14s and special operations commandos with the SCAR Heavy, for example) use the larger 7.62mm (i.e. .30 caliber) round.
The M4 is the standard weapon of vehicle drivers in Iraq, the M16 is the standard weapon of infantry troops. Both are automatic weapons (which means that they can fire multiple shots with a single pull of the trigger). The M4 and M16 differ mostly in length, with the M16s longer barrel making it more accurate at long ranges and more potent. The M14 used by snipers is designed for very long range, highly accurate shooting, usually with one shot at a time.
In a nutshell, the smaller round has the virtues of institutional inertia, standardization with allied forces, and lower recoil. The larger round has greater stopping power. Some participants in the discussion have urged an intermediate sized 6.8mm (0.27 caliber) round.
There are other reasons to replace the current Vietnam era M4 and M16. Newer designs are less prone to jamming in extreme conditions, for example, and can be built to be somewhat lighter than existing weapons. But, advocates for a larger round say those considerations are secondary to caliber, while advocates for the existing caliber also argue that jamming isn't a big enough concern to justify replacing the M4 and M16, since it is rare in any case.
The debate has an almost religious character. Advocates of each position are deeply entrenched. No one seriously doubts that the M4 or M16 are inadequate for most purposes, but advocates for change argue that we can do better. Supporters of the status quo argue that user training is the problem and that stopping power is not inadequate. Supporters of change argue that the current round doesn't kill with a single round as often as it should.
The absence of support for the larger round within the Department of Defense establishment, despite such a widespread call for it among former military outside critics is hard for an outsider to read. Likewise, the technical arguments are hard for someone who isn't personally a gun expert to evaluate. Too many real experts come out on opposite sides of the debate. Also, the Army's recalcitrance on providing soldiers with body armor, armoring Humvees, and deploying mine resistant vehicles in the current conflict, and unwillingness to confront evidence of the jamming problem in the current carbine and rifles relative to newer models has undermined its credibility on this issue.
While replacing the small arms used by U.S. troops would cost money, the amount of money involved is very modest. A new rifle or carbine for every soldier in the U.S. Army would cost less than $1 billion, a tiny piece of the overall defense budget, and less than the cost of a single typical naval ship or a handful of jet fighters, for something that almost all troops on the ground carry with them as their primary weapon every day. Spread over two or three years, it would be a pittance which Congress would easily agree upon if the Defense establishment recommended it.
I personally am agnostic on the caliber issue, but it is clear to me that a redesign of the M4 and M16 is in order, and it is likewise clear to me that the caliber issue ought to receive a fair hearing from experts independent of the current procurement brass.
Meanwhile, in a related story that wasn't covered in this particular pair of articles, there has been considerable dissatisfaction expressed with the standard issue Army pistol (more so than almost any other equipment used by U.S. troops in combat), but an effort to replace this has also derailed. Once again, I'm not an expert on why soldiers in the field dislike this gun. But the pistol issue would be an even cheaper problem to address because it would be easier to use commercial off the shelf replacements (since it does not require an automatic weapon and because many quality pistols are used by law enforcement), and because each gun is less expensive.