Apparently, it is difficult to replace perfection

For reasons known only to God and the Army, the Army apparently is attempting to replace the M2 .50 caliber machine gun, affectionately known as the Ma Deuce. The M2 has been in the US military's inventory since 1918, designed by legendary gun designer John Browning. It has been used in every role imaginable, on armored vehicles and tanks, on a tripod as an infantry weapon, in aircraft and pretty much any other role you can think of for a machine gun.

It has done so extremely reliably, as well. The Army recently discovered an M2 that had been in service for 90 years without need of repair.  Hell of a weapon, there. Naturally, the Army wants to replace it:

The US Army has begun a program to create a lightweight .50 caliber machine gun to replace the venerable M2 Browning. The program will, like the M240L machine gun, use titanium to reduce weight by 20-30 percent. Scout.com and NationalInterest.org both have stories on the subject. The following is from Scout.com:

The Army is creating a new, lightweight version of its iconic .50-cal machine gun designed to better enable Soldiers to destroy enemies, protect convoys, mount weapons on vehicles, attack targets on the move and transport between missions.
The new weapon, engineered to be 20-to-30 percent lighter than the existing M2, will be made of durable, but lighter weight titanium, Army officials said.
The emerging lightweight .50-cal, described as still in its infancy stage, still needs to be built, riveted and tested.

As the Firearm blog notes, this is not the first time the Army has tried to replace the M2 with a lighter weapon. The blog also notes that trying to create a lighter .50 caliber machine gun tends to ignore physics, as the weapon has to be a heavy, rugged piece simply to adequately perform its role. Earlier attempts ended in failure:

The two latest attempts to replace the M2 were the XM312, a lightweight, long-recoiling .50 BMG machine gun derived from the 25mm XM307 ACSW (and which was originally intended just as a test bed for that larger-caliber weapon), and the XM806 LW50MG. Both of these were cancelled, despite each being half the weight of the M2.
What both the XM312 and XM806 programs found is that there is a serious contradiction in having a lightweight .50 caliber machine gun, especially one that compromises the performance of the weapon in some way. Automatic weapons in this caliber, due to their massively heavy ammunition, virtually cannot be used as dismounted weapons, and must be used mounted to either a vehicle, aircraft, or tripod. As a result, the benefits of lightening the weapons even substantially does not create a major improvement in usability for the weapons,

We'll see what happens. My money is on the M2.