Lightweight Polymer Cases Could Be a Silver Bullet for Marine Corps Ammo

U.S. Marine Corps Cpl. Jamaury M. Jimenez, a machine gunner with Advanced Machine Gun Course (AMGC) ... [+] 1-22, fires polymer rounds from a .50-caliber machine gun at Marine Corps Base Camp Pendleton, California, Nov. 3, 2021. (U.S. Marine Corps photo by Cpl. Cameron Hermanet)

Every caliber of ammunition the U.S. military shoots has at least one thing in common - a brass/metal casing. New polymer .50 caliber machine gun casings now testing with the Marine Corps hold the promise of lighter weight, recycled material and less wear and tear on weapons.

The standard brass cartridges that encase rounds today have been in use in a similar format since before the 1898 Spanish-American War. They remain effective but the miliary began to look at casing different caliber rounds in polymer material as far back as the 1950s. The polymers used for ammunition casing then, and now, are essentially synthetic plastics with different proprietary formulations.

Experiments with polymer-cased rounds in the 1980s and early 2000s showed potential but the technology was not yet mature enough to warrant evaluation for broad acquisition. However, defense suppliers like Textron TXT and True Velocity kept developing different polymer casings and round types.

Their progress was noted and in 2016 the Joint Lightweight Ammunition Integrated Product Team (JLAIPT) was stood up by the U.S. Army, the U.K. Ministry of Defence and the U.S. Marine Corps to collaborate in developing polymer cased ammunition.

The UK's effort centers on developing polymer casings for 5.56mm rounds for the British Army's SA 80A2 Individual Weapon and the U.S. Army's M249 Squad Automatic Weapon. The U.S. Army is developing 7.62mm polymer ammunition used in Army and Marine M240 machine guns and some sniper weapons. The Marines have been tasked with developing larger still .50 caliber (12.7mm) rounds for the Corps’ "Ma Deuce" M2 machine gun.

MAC .50 Caliber (12.7mm) Polymer Ammunition with nylon links.

In January 2020, Marine Corps Systems Command (MCSC) awarded a little-known Mississippi-based firm, Nammo-MAC LLC, a nearly $10 million small-batch production contract to make polymer cased .50 caliber ammo for the M2. Last November, Marines with 1st Marine Division tested and assessed polymer ammunition during a limited user evaluation at Camp Pendleton, CA.

The chief reason for doing so is weight. When the JLAIPT was formed, its chief goal was reducing the weight of ammunition by at least 10 percent. Multiple DoD studies have shown that contemporary tactical gear, communications equipment, smart devices and associated batteries, along with body armor have pushed individual Marine/Soldier loads well over 100 pounds. The weight degrades their physical and ultimately mental performance.

Lieutenant Colonel Brian Wisneski (USMC) is deputy program manager for MCSC's PM Ammunition. He says the polymer-cased ammunition produced by Nammo-MAC is approximately 1.2 ounces lighter per round than standard .50 caliber ammo, about a 23% weight reduction.

"That equates to seven pounds per metal can which has 100 rounds in it and 14 pounds per wirebound box," Wisneski says. "That's just the ammunition itself." MCSC is also looking at replacing the traditional metal links used to secure .50 cal ammunition in belts with nylon links.

An M2A1 wirebound crate with two 100-round cans of .50 caliber ammunition.

The combination could yield further weight savings with significant logistics and operational implications. Metal cans of .50 cal ammo come in pairs in wirebound wood boxes for shipping. The typical 48 wirebound boxes shipped on a pallet would be 672 pounds lighter if filled with polymer cased ammunition.

"We can trade that weight off for other gear or another few Marines on an aircraft," Col. Wisneski affirms. The savings could also be realized as range and fuel consumption positives for a variety of platforms. The Marines’ Light Armored Vehicle (LAV-25) for example would save 200-300 pounds depending on loadout with polymer .50 cal rounds according to Wisneski.

USMC helicopters, MV-22s and other .50 caliber-equipped aircraft would benefit from the weight saving as well. Lighter weight casings would theoretically gain in value as polymer ammunition is extended to larger 20mm and 30mm rounds.

PM Ammunition is undertaking environmental/durability testing of the plastic cases as well as fire testing. So far, they appear to be as robust as brass casings in shipping, storage and life cycle scenarios "There really aren't differences per se between brass and polymer cases," Wisneski asserts. "We’ve found nothing concerning."

The environmental impact of polymer cased ammunition is an issue that has prompted the Corps’ to look at the possibility of making it a cyclical asset.

"It's plastic and everybody looks at plastic as a bad thing," Wisneski acknowledges. "We’ve asked, how could we use it with 3D printing if we need to make a repair part and we have 600 rounds of polymer .50 caliber that we can harvest?"

The answer isn't yet clear but the idea of recycling polymer cartridges is an appealing one as is ammunition which promotes longer weapons life. Brass casings conduct heat during the ballistic [firing] evolution PM Ammunition says. The brass superheats and then transfers that heat to the chamber of the weapon. Conversely, polymer insulates the chamber from that heat.

"Where brass expands - whatever the minute percentage is - in the chamber, it holds that for a second. A polymer will expand and [contract immediately]," Wisneski says. Lower mass has a positive effect too.

Polymer-cased .50-caliber ammunition is seen at Marine Corps Base Camp Pendleton, California, Nov. ... [+] 3, 2021. (U.S. Marine Corps photo by Cpl. Cameron Hermanet)

"Because of the reduced weight of the round, the [M2] feed mechanism and extractor don't have to pull as hard to [eject the spent casing]."

Together with its thermal benefits, the lighter weight of polymer-cased ammunition should impart less wear and tear to the weapons firing it and likely increase their combat capability.

"The weapon with polymer ammunition [effectively] has a higher rate of fire because the weapon doesn't choke [hesitate] because the polymer casing dissipates heat and reduces friction," the Colonel points out.

Significant testing remains before scaling to full production and there are questions about cost at scale. Col. Wisneski, who has a career background in ammunition logistics in the USMC as an enlisted rating and an officer, opines that ammunition manufacturing is "black magic" with many variables. The small batch run of ammo that MCSC has thus far experimented with is more expensive than traditional .50 caliber ammunition.

Would a large run of polymer .50 caliber ammunition at the U.S.’ Lake City Army Ammunition Plant be cost competitive?

While offering no specific projection and pointing out that military and commercial ammunition costs are cyclical, Wisneski says, "We believe the [mass] production prices will come down to be near the cost of brass [casings] right now."

DoD had planned to begin introducing polymer ammunition 2022 but the schedule looks to have slipped to 2023 or beyond.

The field evaluation at Camp Pendleton was largely positive Wisneski reports but there are always nuances. While there, he asked two Marine machine gunners who fired 1,200 .50 caliber brass rounds then directly switched to polymer rounds what they thought. A young Lance Corporal told him, "Sir, the cans are loaded backwards."

A standard ammunition can lid opens up and to the left until vertical. The first round of brass ammo comes out on the opposite [right] side. At the Evaluation the Marine found that the first round of polymer ammunition came out on the left side of the can, next to the lid Wisneski relates. The gunner had to reach across the [gun] chamber moving his hand another 8 to 10 inches to load the weapon.

"The gunner said, ‘Sir, that's two seconds [more time], that's me reaching across the hot chamber, that's muscle memory that you just messed up because the cans are loaded a different way."

"Even through all of our processes, I never thought of that," the LtCol admits. "Here's a young Marine who's going to use [the polymer ammo] in his daily craft, telling us this is something we need to change."

It could be argued that Marines and Soldiers, weighted down by modern warfare, have been telling the military it needs a silver bullet to lighten the load for a long time.