August 23, 2012:
Photos from China show Chinese infantry carrying around the QBZ 89 12.7 (.50 caliber) machine-gun and using it in field exercises. The QBZ 89 is lightweight (17.8 kg/39.2 pounds for the machine-gun and 8.5 kg/18.7 pounds for the tripod), at least compared to older 12.7mm machine-gun designs. The American M2 12.7mm machine-gun weighs 38 kg (83.8 pounds), plus another 20 kg (44 pounds) if a tripod is used. For that reason most M-2s are mounted on vehicles. The U.S. designed and built a lighter (18 kg/40 pounds) XM806 but it had only half the rate of fire (250 rounds a minute) as the M2 and that was a major disappointment to the troops. The most recent M2A1 can handle quick barrel changes. Each barrel weighs 10.9 kg (24 pounds). There is also a mounting rail for scopes and a flash suppressor and fixed headspace (which makes the weapons easier to use).
The big problem with a portable 12.7mm machine-gun, no matter how light, is the weight of the ammunition. Each round weighs 117 g (4.1 ounces). Thus a hundred rounds would weigh 11.7 kg (25.7 pounds). That much ammo can be fired in less than a minute.