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Weekly UpdatesEfforts to lighten soldiers' loads have focused on reducing the weight of body armor and shrinking the size of batteries and other equipment that they carry into combat. But for machine gunners, the bulk of the weight--about 40 pounds--is in the weapon and ammunition that they lug.
Technologists are working to cut small arms weight in half without compromising firepower, and so far prototypes of a redesigned machine gun and ammunition are demonstrating the art of the possible. Engineers are applying those lessons to build a lighter assault rifle that would help decrease the average soldier's combat load, too.
"We've really proved the feasibility of reducing the weight," says Kori Phillips, project management engineer for the joint service small arms program office at the Army's Armament Research, Development and Engineering Center at Picatinny Arsenal in New Jersey.
A team of contractors led by AM Corp. has developed a weapon system that reduces by 43 percent a soldier's combat load. "That's a big deal to a guy carrying this stuff up in the mountains of Afghanistan," Phillips says.
Using the M249 squad automatic weapon and the M855 5.56mm ammunition as baseline references, the team was able to develop prototypes that reduce the weight of the machine gun by 45 percent and the weight of ammunition by as much as 50 percent.
Unlike previous efforts to lighten the load by substituting metal components in existing weapons with different materials, the team has taken a "dean-slate" approach in developing the new technologies from scratch. The only requirements were that engineers had to design the weapon around the existing 5.56mm bullet while also preserving the muzzle velocity, lethality and accuracy of existing firearms and maintaining similar price points for affordability.
"We've basically redesigned the weapon and the amino together so that we could address those issues," says AAI's Paul Shipley, program manager for the lightweight small arms technologies program. "That's the breakthrough, in that you have to treat it as an entire weapon system."
To make the ammunition lighter, engineers honed in on the bullet and redesigned the cartridge so that it incorporated polymers. The revision yielded two technolo gies: a cased telescoped ammunition round, which resembles an old-fashioned spyglass folded up; and a caseless telescoped ammunition round.
In the cased ammunition variant, a plastic shell arrangement replaces the traditional brass found in conventional cartridges. The bullet fits inside the cylindrical container along with the propellant.
None of the other components was altered, says Phillips. The bullet, the propellant and the primer are all the same, but the team managed to reduce the weight of the case so significantly that the weight of the entire round dropped by 40 percent.
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In the caseless version, the propellant is a solid mass in which the bullet fits. With a hefty structural design, the propellant can withstand the handling load, so the need for a case is eliminated and the weight of the ammunition itself is cut in half. When the bullet is fired, the propellant bums inside the weapon.
Both cartridges are of the same length, but the caseless variant is slightly smaller in diameter. It also poses more technical risk in the manufacturing process, Phillips says.
Current firearms in the military's arsenal cannot fire the prototype ammunition. They are only compatible with the program's light machine gun, which has a new cartridge feed mechanism. "We couldn't divorce the two and still get to the weight goals that we were trying to achieve," says Phillips.
Creating a lightweight machine gun capable of shooting the two rounds required a new configuration. In traditional firearms, such as the M249, the firing chamber is attached to the barrel. A bolt in the weapon engages the ammunition belt and pushes a round down a ramp and then forward into firing position inside the chamber. The cartridge experiences dynamic action in the process, Shipley says.
In the new light machine gun, the cartridge has a smoother transit because the weapon has a pivoting chamber that is not attached to the barrel. The chamber, which is aligned with the ammunition belt, rotates around an axis. When it is out of line with the barrel, the round feeds through and is placed directly into the chamber. To shoot, the chamber pivots down in line with the barrel.
"That simplifies the feed mechanism considerably," says Shipley.
After the round is fired, the empty bullet case is pushed out the front end of the weapon by a new cartridge, rather than ejected out the back as in current systems.
"It's like going through the Lincoln Tunnel," explains Phillips. Having the bullet trajectory and case ejection in the same direction in the gun lessens the chances for jams. "It is a smoother operation for the weapon system and it cuts down on typical reliability problems, which are failure to feed and failure to eject," says Phillips.
In traditional firearms, the heat generated by repeated shots can melt non-metal materials in the round. Because a pivoting chamber is employed in the prototype, barrel heat does not transfer readily, which enables technologists to use the plastics in the ammunition case.
Other than the chamber, much of the conventional machine gun's structure and functionalities have been preserved in the light machine gun prototype. "We've just designed them for optimal arrangement to reduce the weight," says Shipley.
Troops who take the M249 machine gun into battle carry at least 600 rounds of ammunition. All together the weapon system weighs 38.3 pounds. In contrast, the light machine gun prototype and 600 rounds of cased telescoped ammunition weigh 23.4 pounds--about 15 pounds less. If troops use the caseless ammunition instead, the total weight drops even more to 19.9 pounds.
"It's not like we're reducing the weight and reducing the capability," says Shipley. "We're giving the same lethality using the same bullet, for lighter weight."
The team also is developing a prototype rifle to fire the lightweight ammunition. Engineers will build the hardware soon, Shipley says, and could scale up the ammunition to 7.62mm rounds if so desired.
Scientists have fired more than 10,000 cased telescoped ammunition rounds on the light machine gun prototype. But the caseless ammunition rounds have been shot only several hundred times. It will take another year of development before the caseless rounds are ready for shooting demonstrations, Shipley says. The team also is working through additional iterations on the caseless design to reduce some cost issues that were identified previously.
A military assessment of the program is scheduled for 2011. The team will build eight machine guns and 100,000 rounds of cased telescoped ammunition for an operational demonstration by the Army's 25th Infantry Division in Hawaii.
The machine gun and ammunition would be ready for mass production in five years at the earliest. But the Army leadership is still not sold on the program.
"Our toughest hurdle is going to be convincing the decision makers that this is the right way to go, that it's worth it," says Phillips. "It's a big step. It's not an evolutionary thing--it's very revolutionary."
Considering that small arms have not changed much in decades makes the redesign a harder sell, but team officials say the lighter weapon is ready to compete against today's machine guns. The program's biggest challenge is not to prove that the technology works but to persuade the Army's weapon buying bureaucracy that this weapon could benefit troops in the field.
"It's getting the interest, getting the requirement, and moving from the technology-based effort into a program of record," Shipley says. "It needs to transition into a program of record to go forward."
Originally, the program was part of the Defense Department's objective force warrior program, which was striving to reduce by 50 percent the weight of gear that troops must carry and wear. The weapons portion diverged from the initiative several years ago, but Phillips says a dialogue has been reinitiated.
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