Army researchers working to lower weight of emerging infantry weapons.

Although composite materials often carry enormous potential for weight reduction, Army scientists are finding that redesign and the combined use of various metal alloys are equally important keys to reliable and easily portable weapons.

The new arms being designed at the Army's Soldier Systems Center in Natick, Mass., use blends of conventional metals, newly developed materials and novel approaches to firearm configurations. Testing that once took years to accomplish now takes months, with the help of computer modeling and advanced testing chambers.

"We're not stubby pencils and blueprints any more," said Lt. Col. Matthew T. Clarke, program manager for individual weapons at Natick.

Replacing parts with new materials is not new. Butt stocks for the M-16 and M-4 were replaced with composite carbon after it was determined that soldiers were cracking the rifle's stocks when they dropped to the ground after a dash. But enhancing performance while keeping the same dimensions as old systems is a hard nut to crack. Researchers say the chance of success is increased dramatically when they design from scratch instead of retrofitting existing platforms with lightweight pieces.

"Brass casings are great. They've been around forever for a reason ... But is there anything other than brass? We're looking at that right now," said Richard Audette, deputy project manager of soldier weapons. "All the solutions so far have been thicker."

One project on the front burner is the XM25 25 mm airburst weapon system. The weapon features a single piece of carbon-fiber composite material making up the weapon's stock and frame, with a titanium barrel and a scattering of internal steel components.

"We think we've gotten the mixes correct," Clarke said. "This represents a significant leap ahead for lethality,"

The XM25 uses a variety of specially crafted munitions, including non-lethal and high-explosive variants, featuring steel warheads and aluminum casings. A shooter lases a target with a range finder as the weapon's internal ballistics processor speaks to the smart round, informing it of environmental conditions. If the shooter wanted the round to explode after entering a room through a window, for example, distance can be manually added to the fuse's timer. The system weighs less than 12 pounds.

The XM25 program enters the demonstration and development phase next summer, Clarke said.

Another new weapon using a radical design to complement composite materials is the XM312, a .50 caliber machine gun with a sliding barrel design that decreases the recoil energies. The barrel and other subsystems are pushed forward by a spring when the weapon is fired, the moving parts reducing recoil significantly. When fired, the barrel appears to move in and out like a sewing machine needle. The system is made from a carefully selected mix of stamped aluminum, composite carbon fibers and steel for internal mechanisms.

The system weighs 29 pounds, plus a 13-pound carbon composite ground mount. The XM312 can be converted to a 25 mm weapon by using a five-part kit. That system, XM307, can fire the same selection of rounds as the XM25 airburst system.

"We design to get as much commonality as we can," Clarke noted. Sometimes composites bring other advantages, such as a lack of corrosion, overall strength and resistance to weather. In other instances, more durable materials are used to replace small plastic parts.

Sand and dust shields, covers, knobs and switches tend to break, and thus are candidates for replacement with new materials, according to Alan Li, lead product management engineer for the XM307. Li's team is researching formulas for magnesium alloys that make robust, temperature resistant small parts.

Designing these small parts is "not very sexy," Li conceded. But anything that keeps guns from jamming is essential for soldiers, and the brass welcomes anything that increases the life span of a military system.

Freshly developed materials come to weapon engineers handicapped by their newness, program managers said. Although the laboratories screen materials for usability, it takes some convincing before trust can be established.

"We tend to use proven products; we're sort of conservative that way," said Lt. Col. Kevin Stoddard, program manager of crew-served weapons. "It has got to work when it has to, so we tend to stick with proven results."

Testing new materials is done in a combination of old-fashioned range shooting and 21st century technology. During the development process, weapons are brought to environmentally controlled firing ranges and test chambers for evaluation. Computer models help predict how tough the material is and pinpoint weaknesses of system materials and design.

"We put the weapons in the same types of environment they have to operate in, and shoot them," Stoddard said. "Even in the test environment we shoot them as a soldier will in the field, three or four times and then a rest."

Arming the next generation of soldiers requires more seamless coordination between systems designers and their counterparts in the labs, according Tim Woo, a materials engineer for the Army's Energetic and Organics Materials lab.

Designing materials in a laboratory is different than incorporating them into a system ready for deployment, Woo said. Not only do systems have to be resistant to external contaminants, the environment of the weapons themselves--with hot gasses, violent motion and rugged storage conditions--take a heavy toll on armaments.

"It's not enough to know how lightweight it is," he said. "We need to know how a composite material will work in this environment."

For that reason, some potential materials have weaknesses to particular stresses that can be only be found in testing. For example, carbon fiber composites that are set in crooked or bent positions do not react well to impacts, a flaw that reduces their performance in tests.

Woo noted that a recent composite material used to create the fins of a 120 mm mortar shell failed drop tests and was rejected from use, despite its lighter weight and good performance in other rests.

As a positive counterpoint, Woo described an advance in the way the 120 mm mortar shells are transported. Instead of a heavy, eight-piece container, his laboratory designed a three-piece pack that reduces the weight by 60 percent through the use of composite materials. Furthermore, the new system costs less, can be disposed in landfills, and better protects the shell's operating ring from impact damage.

Woo added that, by using composites, his lab is close to designing a 5.56 mm training round with a weight reduction of 30 percent.