Defense contractor Textron just unveiled a new rifle at the Modern Day Marine conference. Designed to use so-called "telescoped" ammunition, the new rifle promises a harder-hitting, lighter bullet for America's ground troops to fire. Whether the U.S. military is ready to embrace all the change a new rifle and ammunition would bring remains to be seen.

Traditional bullet cartridges have a bullet seated roughly halfway inside a brass shell casing, with gunpowder inside the casing. By contrast, the new rifle uses a 6.5-millimeter polymer-cased telescoped bullet. Telescoped rounds feature a bullet completely encased in a polymer shell, like a shotgun, with gunpowder surrounding the bullet in the shell.

The result is a cartridge that doesn't use brass, a considerable savings in weight. According the Kit Up! blog, telescoped ammunition is about 40 percent lighter than traditional ammunition. Textron could have channeled this weight savings into making lighter ammunition, but instead it chose to make new ammunition that packs a bigger punch. The rifle—and 20 rounds of ammunition—weighs a total of 9.7 pounds. By contrast, the standard M4A1 (pictured above) and 30 rounds of ammunition weigh 8.74 pounds.

Textron claims the new 6.5-millimeter round has 300 percent more energy than the standard U.S. Army bullet, the M855A1. That translates into greater knockdown power against human targets, more armor penetration, and longer range. A heavier bullet and more energy would solve a persistent complaint about the U.S. Army's M4A1 carbine—that the smaller 5.56-millimeter bullet often requires multiple hits to incapacitate a target and it lacks the range to make accurate long-range shots. The latter has been a particular complaint in Afghanistan, where long-range engagements are common.

Textron's rifle is a gas-operated, piston-driven rifle that has many familiar features drawn from the M4A1, including a charging handle and gas block. It features military-standard rails for the attachment of devices such as flashlights and lasers, and what appears to be Advanced Armament Corporation flash hider. The front and rear sights, pistol grip, and buttstock are all from firearm accessory manufacturer Magpul.

Tellingly, the 20-round magazine is at least as long as a standard M4A1 30 round magazine. While a 30-round magazine may be possible, too long a magazine blocks the user from shooting while prone. In fact, it appears polymer-encased telescoped rounds are actually wider than brass rounds. While each round is lighter, it takes up more volume than its brass-encased peers.

If that's the case, then Textron's design choice is understandable—if you must carry fewer bullets anyway, you might as well make them hit harder. There are always compromises in small arms design, and the new rifle is no exception. Is losing a third of available ammo and adding three quarters of a pound to the rifle worth a 300 percent increase in bullet energy? Decisions, decisions.

Will the Army adopt the new rifle and ammunition? The U.S. Army is notoriously cheap when it comes to small arms, and institutional inertia is strong. The -A1 upgrade to standard M4 rifles is only a few years old and conversions are still taking place. We also don't know the cost of the rifle and—more importantly—the ammunition, which will be purchased and stockpiled in the billions.

Still, if Textron can build a rifle that is reliable and inexpensive, and if the Army accepts the design tradeoffs inherent in the telescoped design, it could be the first all-new rifle design fielded by the Army in 51 years.

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