Replacements for the M4A1

Three Rifles That Could Replace the Army's M4A1 Carbine

The Army is "taking a hard look" at new arms for soldiers.

U.S. Army photo by Sgt. William A. Tanner
 
By Kyle Mizokami

In new comments to the Senate Armed Services Committee, U.S. Army Chief of Staff Mark Milleyhas said the Army is "taking a hard look" at a new German assault rifle and other designs to replace its existing weapons.

The M4A1 carbine is currently issued to U.S. Army combat troops worldwide. A descendant of the original M16 rifle, the M4A1 has a 14.5" barrel, is chambered for the 5.56-millimeter round, and weighs approximately nine pounds when fully equipped with optics, lasers, foregrips, and other attachments. There are concerns in Congress, however, that the M4A1 could not penetrate modern Russian body armor, which is what prompted Milley's comment.


Marine fires his M27 Infantry Automatic Rifle.
U.S. Marine Corps photo / Lance Cpl. Jonathan Sosner

With those specifications in mind, what new weapons could replace it? One possible replacement weapon is the Heckler and Koch 416. Outwardly (and inwardly) similar to the M4A1, the 416 differs in using a gas piston system in which hot pressurized gas generated by burning gunpowder drives a piston that ejects empty brass casings, chambers a new round, and cycles the gun's action. The HK serves with the Marine Corps as the M27 Infantry Automatic Rifle, with several issued to each squad and likes them enough to consider issuing them to all marine infantry. The HK416 is also the new official rifle of the French Army.

Arguments for: Unlike the M4A1, which injects the hot, dirty gunpowder gases into the gun's action, the 416 vents the gasses outward. The result is a rifle that runs much cleaner. So called "piston guns" also run much cooler, meaning it takes them longer to overheat.

Arguments against: The HK416 is still a 5.56-millimeter firearm, so the Army would need to focus on continuing to make the diminutive round not only capable of penetrating future armors but causing lethal injuries, an increasingly difficult task. A gas piston rifle is slightly heavier and costs three times as much as a M4A1.


AR-10 set up for distance shooting. Note the larger magazine well for longer 7.62-millimeter bullets.
Via Flickr.

Another possible replacement is the AR-10 rifle. The AR-10 is a derivative of the civilian AR-15 rifle, which is functionally identical to the M4A1 -- minus the ability to fire fully automatic. The AR-10 is slightly larger and heavier than the AR-15 and is chambered for the 7.62-millimeter round. The Army's version would be capable of fully automatic fire.

Arguments for: The 7.62-millimeter round is larger than the current 5.56-millimeter round and more likely to both penetrate the body armor of enemy soldiers and incapacitate them. The larger round is also more effective against enemy troops in cover and vehicles. Finally, adopting an AR-10-type rifle would mean the entire infantry squad -- including machine gunners carrying the M240 medium machine gun -- would use a single type of ammunition.

Arguments against: The heavier round also means more recoil, and is more difficult to control firing fully automatic. Soldiers will also be able to carry fewer rounds on them. Finally, the Army would have to get rid of billions of rounds of 5.56 rounds it has stockpiled, although it could compromise by having truck drivers and support personnel continue to carry the M4A1.


Graphic representation of the Textron LSAT rifle.
Via US Army Readiness Command.

Finally, the Army could finally enter the plastic age and adopt a new carbine developed by Textron. Developed under the Army's Lightweight Small Arms Technology program, the rifle uses specially developed bullets. Unlike regular rounds, which have the bullet peeking out from the top, 6.5-millimeter bullets are fully encased in polymer and gunpowder, reducing their overall length.

Arguments for: The new 6.5-millimeter round has 300 percent more energy that the current 5.56 millimeter round, which translates into greater penetration. Like the HK416, the LSAT rifle is also a piston design, so it too will need less cleaning and more firing time to overheat.

Arguments against: The new 6.5 round is heavier and bulkier than the current 5.56 round, meaning soldiers can carry fewer rounds. Textron's rifle is also nearly pound heavier than the M4A1, although at the time it was introduced the company hadn't yet tried to optimize the weapon's weight. Finally, the Army would have to buy billions of 6.5 rounds and distribute them troops worldwide.

If none of these arguments for a new rifle don't sound compelling enough to warrant a totally new rifle you're not alone in thinking so. Small arms development has largely plateaued, and while advances such as the new 6.5 round bring new advantages, they also bring old disadvantages -- particularly weight issues. While the Army in the Age of Trump could do something big and bold by adopting a totally new rifle and bullet, the safe money is on it doing nothing at all, except perhaps fielding a new armor penetrating 5.56 bullet.