Now its official, the U.S. Army is building a replacement for the 1920s era M-2 .50 caliber (12.7mm) heavy machine-gun. The new weapon, the M-307, has been designed so it can fire either the computer controlled 25mm smart shell or (by changing the barrel and receiver), .50 caliber ammo. The troops will begin receiving the new weapon in three or four years. 

The M-2, nicknamed Ma Deuce by the troops, has been around so long because it was very good at what it did. Accurate, reliable, rugged and easy to use, many of the M-2s currently in use are decades old. The army doesnt want to build new ones, and wasnt sure it could do without the venerable, and very useful, Ma Deuce. So instead of going ahead with the plan to build a new .50 caliber machine-gun (the XM312), the manufacturer of the XM307 (General Dynamics) was given the go ahead on manufacturing their weapon with the stipulation that it be convertible to a plain old, non-computer, .50 caliber weapon by quickly swapping out a few parts. The XM312 was only eight pounds lighter than the 50 pound XM307, as the electronic component of the XM307 is not all that heavy, just expensive and always in need of fresh batteries. Maybe theyll get in the habit of slipping a fresh battery into each box of 25mm ammo. 

Aside from the .50 caliber ammo being 20 times cheaper than the high tech 25mm stuff, if there are teething problems with the computer controlled weapon, the troops will still have a spiffy new version of the old M-2. An XM307 with a .50 caliber barrel is still 14 pounds lighter than an M-2 and can use some aspects of the fire control electronics (like the range finder). 

The 25mm XM307 was developed from the 1990s project to produce a 20mm computer controlled shell for an infantry weapon, as well as a heavier crew served weapon (the XM307). The 20mm shell proved to be rather less lethal than was required, so it was decided to move up to 25mm. The infantry weapon (the OICW) combined the 25mm weapon and a 5.56mm rifle in one unwieldy arrangement that has now been dropped. There will be a semi-automatic 25mm weapon (the XM-25) for the infantry (that looks and feels like a hefty shotgun) and the automatic XM307 (which weighs 50 pounds and fires the 25mm rounds at the rate of about 250 a minute, or four a second.) The computer controlled 25mm round, at over 20 bucks each, can also be fired one at a time. This will often be sufficient, because the XM307 has a built in range finder that can put a 25mm round through a window, and have it detonate inside the room. This can be very useful, and theres no need to put dozens of rounds through the window, as is the case with the current .50 caliber weapon. The XM307 can also fire more conventional armor piercing and incendiary shell. The major problem with the XM307 is that this new computer controlled stuff has not been used in combat yet. Until it is, no one will be quite sure just how much of an improvement it is over Ma Deuce.