The M4A1 carbine is currently the standard rifle issued to US Army combat troops worldwide. It is a direct descendant of the legendary M16 rifle that was originally designed during the Vietnam conflict, and is generally considered to be an excellent weapon.

However, in recent comments to the Senate Armed Services Committee, U.S. Army Chief of Staff Mark Milley has has said that the Army “taking a hard look” at replacing the carbine with a new weapon. He specifically mentioned a new German assault rifle as among the candidates.

The comments come in response to concerns in Congress. Some experts have noted that the M4A1 is no longer capable of penetrating the most modern types of body armor. Some people therefore feel that the dependable carbine should be replaced with a more powerful rifle.

The question, though, is what rifle could possibly replace the M4A1. Looking at the specifications, it is hard to believe that any other rifle will provide the same level of performance. The M4A1, as standard, is chambered for the 5.56mm round, and has a 14.5” barrel. When fully field-equipped with a scope, lasers, and additional grips, it weighs in at an impressively light nine pounds.

In addition, the M4A1 is highly regarded by combat troops for its reliability and ability to stand up to the rigors of field deployment. If Congress wants US troops to carry a more powerful rifle, they are going to have a find a good replacement. Let’s take a look at some of the options.

The Heckler and Koch 416

One possible replacement for the M4A1 is the Heckler and Koch 416. On the surface, this gun looks very similar to the M4A1, and it incorporates many of the same design features. However, there is one bug difference between the 416 and the  M4A1 – the 416 uses a gas piston system to cycle rounds.

This system uses the hot pressurized gas generated by firing rounds to drive a piston. This piston ejects empty casings, chambers a new round, and re-sets the guns action. “Piston guns” such as these are regarded as more reliable than the M4A1, which ejects these gases inside the action of the weapon. They run much cleaner than standard carbines, and because hot gases are ejected from the weapon they also stay much cooler, reducing the possibility that the rifle will overheat.

The 416 also has the advantage that it is already in use by the US Marines. It is issued to some Marines as the M27 Infantry Automatic Rifle, and the service has found them good enough to consider issuing to all of its combat troops. The weapon is also the standard rifle of the French Army.

There is a big problem, however, with the 416 as a replacement for the M4A1 – it is also a 5.56mm rifle. If the aim is to improve the power of the rifle issued to US troops, this makes it an unsuitable choice. And then, of course, there is the price: gas piston rifles like the 416 are not only heavier than the M4A1, they also cost three times as much.

The AR-10

A second option would be the AR-10 rifle. This gun is a military adaptation of the civilian AR-15, both of which are essentially identical to the M4A1. However, the advantage of the AR-10 is that it fires the 7.62mm round, giving it more power.

The AR-10 is a little larger than the M4A1, and currently lacks the ability to fire fully automatic. It is expected, though, that if the Army goes for this option, an AR-10 with fully automatic capability will be produced.

There are several reasons why the AR-10 might be a good choice to replace the M4A1. The 7.62mm round is much more likely to penetrate body armour, and is also more effective against troops behind cover and enemy vehicles. In addition, the 7.62mm round is already used in the M240 Medium Machine Gun, and so adopting this round for rifles would mean that infantry squads only have to carry one type of ammunition. This makes logistical planning much easier, and improves the adaptability of infantry squads.

There are problems, however, with using the 7.62mm round. For a start, a larger, heavier round generates more recoil, and makes hitting targets with fully automatic fire much more difficult. Larger rounds are also more difficult to carry, meaning that each soldier will be able to carry fewer rounds. And finally there would be the problem of the mountains of 5.56mm rounds the Army has already bought, which would have to be scrapped.

The Textron 6.5mm Carbine

The last feasible option is a new weapon developed by the Army themselves. The Textron 6.5mm Carbine uses specially designed bullets to generate plenty of power in a compact design. Unlike normal rifle rounds, in which the bullet protrudes from the end of the cartridge, the innovative 6.5mm bullet is totally encased in polymer and gunpowder, reducing size and weight while also providing plenty of power.

Though this rifle is still under development, and some issues need to be worked through, it could be a good option. The new 6.5mm round has 300% more power than the standard 5.56mm bullet, and so offers increased penetration. In addition, the Textron Carbine is also a gas-piston rifle, and this could make it more reliable than the M4A1.

On the other hand, the 6.5mm cartridge is still bigger and heavier than the 5.56mm one, so troops will be able to carry less ammunition. And of course, the Army would have to order billions of 6.5mm rounds, and distribute them across the globe.

What Will Happen?

All of these rifles have some pretty big failings as a replacement for the M4A1. Though the 5.56mm round might be regarded as underpowered for modern infantry troops, swapping to a larger bullet would bring huge costs, and limit the amount of ammunition troops can carry.

It is therefore likely that, in reality, nothing will change. Despite the range of options available, the safe money would be on the Army sticking with the M4A1, and developing an armor piercing 5.56mm round to try and get the maximum penetration from it.

Military expert Sam Bocetta, a writer at Gun News Daily.