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A large ball of fire burst from a 120mm barrel as the Army's XM360 tank gun sent rounds at 1,300 meters per second through a mesh target 1 kilometer away at Aberdeen Proving Ground, Md. The March 14 test was part of the Army's evaluation of the first six of the guns.
"The 120mm gun you are seeing here is the most advanced and the lightest in the world," said Dave Smith, a design team leader with the Army's Benét Laboratories in Watervliet, N.Y.
The 4,100-pound XM360 is about one-third lighter than the 120mm cannon on the Abrams tank, thanks to a special steel wrapped in composites, yet is designed to hit targets up to 8 kilometers away on the move and up to 12 kilometers while stationary, far more than the Abrams' 4-kilometer range. Each gun will be expected to fire about 12,000 rounds during its lifespan.
"We wanted to have all those capabilities in a lighter package, a smaller package and a more durable package," said Bob McAllister, the Mounted Combat System primary weapon assembly lead for General Dynamics Land Systems.
The XM360 is intended to go on the MCS, one of eight 27-ton vehicles under development for the Future Combat System. Putting such a powerful gun on a relatively light vehicle required innovation.
"Historically, there has been the ‘big gun, little vehicle' problem, where the little vehicle comes apart eventually," said Emory Thompson, the Aberdeen test center director for the XM360.
To solve that problem, engineers worked to design the gun and vehicle together from the start. The gun has a "muzzle break," a 1.5-foot area filled with small holes to diffuse energy from the gun blast.
"With this gun, we are actually sending that blast to the sides as well as forward, so you don't get the kickback into the vehicle," Thompson said.
The muzzle break was redesigned several times through testing, using small blast overpressure gauges that measure the stress of firing the gun on the vehicle. For the Abrams, the trunnion reaction force — the force exerted on the vehicle when the gun fires — is 140,000 pounds. With MCS, the force is 85,000 pounds, FCS spokesman Paul Mehney said.
That's important for making sure that firing isn't going to shake loose the vehicle's crucial sensors and networking gear, said Army Lt. Col. Bob Hannah, who manages the MCS program.
"The last thing we want is to shoot around and blast that stuff off. We want to make sure the sensors can overcome the pressure," Hannah said.
The MCS will have an ammunition data link to provide the gun and its rounds with target information and a fire-control system that can share target information with nearby units, Hannah said.
"An Abrams has two separate sights, which use an ability we call ‘hunter-killer,' where one sight finds the targets and marks it, quickly moving the gun to the target," he said.
But the MCS will be able to use any fire-control-quality sensor on the battlefield network to line up its own gun, Hannah said: "We will gather the data, fuse the data and get everybody a common operational picture. Now, I have the ability to cue to anyone else's targets."
Prototypes will be ready by 2011, he said.
"Once they receive safety certification, the guns will be delivered to [General Dynamics Land Systems] for integration onto vehicles into a sequential manner. After the guns are done, we will take them out into a tactical situation for operational testing with soldiers," Hannah said.
In the meantime, the Army intends to test by this fall the XM360 with the Mid-Range Munition (MRM), a high-tech 120mm guided round that can home in on a laser or use a 3-inch camera to look for patterns as it falls toward its target. With MRM rounds, the gun will be able to take incoming target data from, say, a UAV with a laser rangefinder.
Initial production of the Raytheon-General Dynamics MRM is slated for 2012, winding up a 63-month system-design-and-development phase, said Army officials at Picatinny Arsenal, N.J.