5mm round

The 5mm Round is a Big Gun ammunition found in the game. 5mm is traditionally belt-fed, and is available in rather high quantities, something made necessary by the notably large "magazine" sizes on the weapons that use it--for example, the Minigun loads 240 rounds at one time and fires an exceptional rate, requiring that the player carries a huge supply if they intend to rely on miniguns.

Description
Generally speaking, the 5mm Round is a common big guns ammunition found in the game, as Super Mutants, especially Brutes and Masters, tend to favor the Minigun. It is quite easy to come by and highly effective later in the game when dealing with large crowds or Super Mutants, though robotic enemies take only marginal damage and Deathclaws seem to be less effected.

By spending time in various areas of Washington, DC, particularly the bunker area found near the Washington Monument, the player can accrue quite a bit of 5mm rounds quickly along with the .32 Caliber Rounds used by Super Mutants carrying Hunting Rifles. Members of The Brotherhood of Steel tend to carry miniguns as well, and with their alarming death rate outside Galaxy News Radio, it's possible to get some 5mm rounds here as well.

5mm rounds are made somewhat obsolete if the player finds a Gatling Laser. On the other hand, it is hard to keep repaired to full condition.