The M2 Browning .50 caliber machine gun — fondly referred to as "Ma Deuce" — is rightly seen as a legend, with over 80 years of service to the troops. This machine gun has outlasted attempts to replace it, including the XM312 in recent years. But if there is one complaint about it – yes, even legendary guns draw complaints – it's that it's too heavy and it only shoots about 635 rounds per minute.
Well, there's not been much progress on the former. The M2 comes in at about 84 pounds, per GlobalSecurity.org. The GAU-19 did a good job addressing the "slow" rate of fire, but it packed on 22 pounds. So, that and the GAU-19's need for electricity rules it out as an option for grunts. But they still want to send more lead downrange.
The GAU-21, also known as the M3M, can fire 1,100 rounds a minute. (Photo from FN America)
Thankfully, there is an answer: the GAU-21, also known as Fabrique Nationale's M3M machine gun. This is a modified version of Ma Deuce that, according to a handout available at the Association of the United States Army's expo in Washington, D.C., is able to fire up to 1,100 rounds a minute. Not quite the 1,300 of the GAU-19, but still very impressive.
The real nice thing is that the M3M does this and comes in at just under 80 pounds. That's a four-pound drop from the baseline M2. Now, the 26-pound difference may not seem like much, but that's 26 pounds that a grunt doesn't have to carry, leaving them more space for ammo, rations, or extra first-aid supplies.
A flight of F-86 Sabres over Korea led by Benjamin O. Davis. Their battery consisted of six M3M machine guns, known today as the GAU-21. (USAF photo)
The M3M can be used on aircraft (one notable user was the F-86 Sabre), land vehicles (often mounted on the same pintles as Ma Deuce), and on naval vessels. It was the secondary armament of the M1097 Avenger, and also was used on OH-58 helicopters. In short, this gun provides a lot of firepower without the weight.