These are the changes coming to US Army and Marine Corps infantry arsenals

The M16/M4 rifle platform, long the standard for the US Army and Marine Corps, could soon be set aside, as officials in both service branches are looking at new options for both weapons and ammunition.

Army researchers are reportedly looking at six different types of ammunition of “intermediate calibers,” according to Army Times.

Those calibers fall between the current 7.62 mm and 5.56 mm rounds and include the .260 Remington, the 6.5 Creedmoor, and the .264 USA, as well as other variants that aren’t available commercially, Army officials told the Times.

The search for alternatives for both weapons and ammo comes in response to concerns with the 5.56 mm round and about the M16 and the M4, which has been continuously upgraded and modified since being first introduced in the 1960s.

Related: This sniper rifle company is trying to lighten the M240 medium machine gun

The M16 and M4 and their variants continue to have problems with jamming, an issue the system has dealt with since its introduction. Improvements in body armor have lessened the lethality of the 5.56 round. Groups like ISIS have also made use of large rounds that outperform the US military’s ammo. (Russia is reportedly working on its own assault rifle using a 6.5 mm round.)

According to some research, Army firefights in Afghanistan, where the US has been engaged for more than 15 years, have mostly taken place at distances of more than 300 meters, or about 1,000 feet. At that range, the 5.56 mm round is far less lethal.

U.S. Army 1st Lt. Branden Quintana, left, and Sgt. Cory Ballentine pull security with an M4 carbines on the roof of an Iraqi police station in Habaniyah, Anbar province, Iraq, July 13, 2011. Ballentine is a forward observer and Quintana is a platoon leader, both with Bravo Company, 2nd Battalion, 325th Airborne Infantry Regiment, 2nd Advise and Assist Brigade, 82nd Airborne Division. (U.S. Army photo by Spc. Kissta Feldner/Released)

At least two studies presented to the US Army have pointed to rounds in the 6.5 mm to 7 mm range as better options.

“Right now the [M16/M4] platform we have is a workhorse and very effective in the hands of a trained soldier or Marine,” Maj. Jason Bohannon, the lethality branch chief at Fort Benning’s US Army Maneuver Center of Excellence, told Army Times.

Going forward, Bohannon said, the Army wouldn’t be able to get more out of the platform and would likely look for a new one.

A report last month from the Marine Corps Times also indicates the Corps is looking to replace the M4 carried by almost every infantry rifleman with the M27, the infantry automatic rifle first introduced in 2010 to replace the aging M249 Squad Automatic Weapon.

Currently, each Marine Corps infantry fire team is equipped with one M27, carried by the automatic rifleman.

“Most Marines like it, and so do I,” Marine Corps Commandant Gen. Robert Neller told Marine Corps Times in April, saying M27s have been “the most reliable, durable, and accurate weapons” carried by rifle squads.

Expanding the use of the M27 would be the most recent of several weapons changes.

In late 2015, Neller approved the move from the M16 to the M4 carbine as the primary weapon for Marine Corps infantry. About a year later, the Corps started testing the M27 infantry assault rifle, which offered a longer effective range, better firing, and more resistance to wear.

A senior Marine officer noted the M27’s rate of fire as a point of concern, suggesting the weapon, which carries 30 rounds and can be fired in full-automatic mode, could lend itself to ammo overuse. (Both the M4 and the M27 use the 5.56 mm round, and the US and NATO militaries have an abundance of that caliber stockpiled.)

One drawback to the M27 is the cost of the rifle, which is produced by German gunmaker Heckler & Koch and runs about $3,000. The M4, built by Colt Defense and FN America costs less than $1,000.

Outfitting the 11,000 Marines — members of companies and fire teams, but not squad or platoon leaders — who would get the M27 under the new plan would cost roughly $33 million, though a Marine Corps official told the Marine Corps Times that cost was not a primary concern during the evaluation process, and the price may change as the Corps continues to inquire with weapons makers.

“I am considering it,” Neller told the Marine Corps Times of the possible change, “but we have to balance improved capabilities and increased lethality with cost.”

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