|For an overview of 5.56mm ammunition throughout the Fallout series, see 5.56mm round. For an overview of .223 caliber ammunition throughout the Fallout series, see .223 round.|
The 5.56x45mm round is a rifle cartridge derived from the .223 Remington, originally developed for the M16 service rifle of the United States Army. It is a rimless, bottleneck cartridge that offers tremendous wounding potential under the right condition. Its performance and popularity among military forces endures despite the Great War: By 2287, it has served Americans for over two centuries, from the United States Army to the New California Republic Army.
The standard type of 5.56mm ammunition, offering good performance to the shooter. Popular among civilians and soldiers alike, it is by far one of the most popular rounds in the wastelands. It can generally be used interchangeably with its parent round, the .223 Remington, due to the same casing, though some weapons might not be rated for the military-grade ammo. In such a case, the 5.56x45mm round can cause dangerous buildup of pressure inside the receiver.
Relatively speaking, the 5.56mm round is the third most common small guns ammunition found in the game, compared to the .32 caliber round and 10mm round. After The Waters of Life, the 5.56 round becomes more common as enemies will use assault rifles more often than .32 hunting rifles. The 5.56mm rounds' world model is a black box magazine (resembling the magazines from the Chinese assault rifle).
Weapons using this ammunition
5.56 rounds are typically found in raider, Talon Company, and super mutant camps. Notable areas to search include Downtown DC and the Metro tunnels underneath the Downtown area. However, 5.56 rounds appear to be scarce early in the game. Large amounts of 5.56 rounds can be acquired quickly through several means:
- At Fort Independence, Brotherhood Outcast Casdin will trade technology items for 5.56 rounds, stimpaks, frag grenades, or RadAway. It is notable that Casdin's subtitles incorrectly say " .556 ammunition" instead of "5.56 ammunition". See the unmarked quest The Outcast Collection Agent.
- In the Fallout 3 add-on The Pitt, completing the quest Free Labor will unlock the ammo press. Located in The Mill of The Pitt, the ammo press converts any ballistics-based firearm ammunition or scrap metal into any other type of ballistic firearm ammunition, including 5.56 rounds.
- Vault Dweller's Survival Guide p.5-17: "Rifle caliber ammunition. The FMJ stands for Full-Metal Jacket, which describes the bullet that is used in the round of ammo. A FMJ bullet is very tough, and has pretty good penetration without sacrificing good expansion. In other words, it‘s an average round."
- Fallout Official Survival Guide p.119: ".223 Full Metal Jacket (FMJ): This is the same ammo used in the late 20th century by various military rifles, including the M-16. A good, basic, hard-hitting round."