Machine-guns have always been popular weapons, because they allow one gunner to put out a lot of bullets, usually something on the order of 400-600 rounds a minute (taking into account time needed to reload.) That popularity has increased over the last decade, as cheaper, lighter and more reliable multi-barrel machine-guns became available. One of the more useful of these has been the Dillon Aero M134D. This is a electric ( battery or vehicle) powered, six barrel 7.62mm machine-gun. The gun itself only weighs 29 pounds. Add the drive mechanism to spin the six barrels, and you have a 66 pound system. Since the M134D fires 3,000 or 4,000 rounds per minute, you need a lot of ammo handy. And that much ammo is heavy, for a thousand rounds of 7.62mm cartridges weighs 63 pounds. Add the weight of the magazine to hold the bullets, and it comes to 125 pounds for a full 1,500 round magazine, and up to 295 pounds for 4,400 rounds. Since you are firing 66 rounds a second, a 4,400 round magazine lasts about a minute. The barrels do not overheat, a common problem with machine-guns, because there are six of them taking turns putting out the bullets. Each barrel is good for 100,000 rounds, and the entire system has, on average, one failure for every 500,000 rounds. However, there tends to be one jam every 30,000 rounds. In helicopters, the M134D is particularly effective, because of the longer ranges the weapon is fired from. With all those bullets going out, you can cover a large area with a few seconds worth fire. On the ground, that much firepower enables you to blast through many buildings, and shred unarmored vehicles. Under those circumstances, the M134D is intimidating to the enemy, and that’s a valuable battlefield advantage.