Replacing the M16: Five lethal candidates

The venerable M16 has been standard issue in the U.S. Army since the Vietnam War. During the ensuing half century, the design has been updated and a shorter version, called the M4, entered Army service in 1997.

Both rifles are effective weapons - as long as they're kept clean. But although it's a newer model, the M4 has not escaped much of the same criticism aimed at its predecessor. Indeed, the rifle is designed in such a way that gas blows into the receiver of the weapon. The resulting buildup of carbon residue has been linked to excessive wear and tear.

What's more, critics have long complained about the two rifles being too sensitive to dust or sand and prone to malfunctioning when used in rugged conditions. More recently, in 2001, the U.S. Special Operations Command found that the M4's design was fundamentally flawed. And in 2006, the military carried out a survey of soldiers returning from combat tours in Iraq and Afghanistan. Some 19% complained about their M4s jamming during firefights - and nearly 20% of that group being "unable to engage the target with that weapon during a significant portion of or the entire firefight after performing immediate or remedial action to clear the stoppage."

Retired Army vice chief of staff Gen. Jack Keane not long ago was quoted not long ago voicing frustration at how long it's taking to find a next-generation replacement for the M16/M4.

"We are not saying the [M4 and M16 are] bad," he told Gannett's Army Times. "The issue for me is do our soldiers have the best rifle in their hands."

Although both the M16 and the M4 have undergone upgrades, they are still considered less reliable and less able to withstand wear and tear than the Kalashnikov assault rifle. Indeed, Keane offered the blunt assessment that that the U.S. military simply has failed to keep up with changes in rifle technology. "We have been sitting on this thing for far too long," he cautioned.

The message seems to have registered. The army has announced an "Industry Day" will be held on March 30. Col. Doug Tamilio, the army's project manager for soldier weapons, says the military wants to challenge "industry to develop the next-generation carbine and we're looking forward to the results."

That may be so but the pressure is building on the military to get off the stick and make a decision that many believe it should have made years ago.

The XM25 Counter Defilade Target Engagement System allows soldiers to hit targets hiding behind barriers. The XM25 operator uses a laser to help compute the distance to the target and then calibrates the microchip-equipped round to explode right above the target's head. The rifle can launch 25mm rounds up to 546 yards at a precise target and 765 yards when firing on a wider area.

A test deployment of prototype X25s has gone well - so well, in fact, that the army now wants more of them sent to its forces operating in Afghanistan. That's a tall order as mass production of the weapon is not planned to begin for another couple of years.

The HK416, which was developed for U.S. special forces, bears an outward resemblance to the M4. But inside, it uses a short-stroke gas system that proponents say constitutes a vast improvement over the M4's design. The rifle has been used by the Army's Delta Force since 2004 after tests determined that the HK14 piston operating system cut down on the frequency of malfunctions while extending the life of its parts.

If he had a vote, Major Chaz W. Bowser, a former weapons developer for the U.S. Army's special operations branch, made clear what his preference would be:

"I could go to Iraq or Afghanistan or anywhere with whatever weapons I wanted to carry. As soon as the H&K 416 was available, it got stuffed into my kit bag and, through test after test, it became my primary carry weapon as a long gun. I had already gotten the data from folks carrying it before me and had determined that it would be foolish to risk my life with a lesser system," he wrote in a letter to Army Times.

The FN SCAR - an acronym for Special Forces Combat Assault Rifles - figures in any discussion of future replacements for the M4 Carbine. In 2009, the rifle was issued to a U.S. Ranger regiment. It features a short-stroke, gas-piston operating system and comes in versions that fire the NATO standard 5.56 caliber as well as the 7.62 caliber bullet. In 2008, the SCAR earned an invitation to the army's Industry Day. With the question of what to choose in place of the M16/M4 still undecided, maybe it will garner a return invite to appear at next month's conclave as well.

REC7, an assault rifle formerly known as the M468 and developed by the Barrett Firearms Manufacturing, looks a lot like the M4. However, it features a short-stroke gas piston system and it fires a different kind of round - the 6.8 x 43 cartridge. The company says the round has 44% more stopping power and a longer effective range than the 5.56 cartridge used by the U.S. Army. The rifle maker was invited the army's 2008 Industry Day to demonstrate a version of the REC7.

Another invite to the U.S. Army's 2008 Industry Day, the XCR assault rifle was in the competition to supply a rifle to the U.S. special forces. However, it was disqualified because of a technicality related to late delivery of blank firing adapters.

The XCR a multicaliber weapon that comes in 5.56mm, 6.8mm Remington SPC and 7.62x39mm cailbers. It uses a long-stroke piston system similar to the one found in the Kalashnikov rifle.