5.56mm round

The 5.56mm Round is a type of small guns ammunition found in Fallout 3 and Fallout Tactics.

Fallout 3
Generally speaking, the 5.56mm Round is the third most common small guns ammunition found in the game, behind .32 Caliber Round and 10mm Round. After The Waters of Life it becomes much more available as enemies start carrying the Assault Rifle in place of the Hunting Rifle. 5.56mm appears as curved grey magazines across the wasteland (resembling the magazines from the Chinese Assault Rifle)

Equipment
5.56 may seem scarce in the early game, but large amounts can be acquired through several tactics:


 * Brotherhood Outcast Casdin (found at Fort Independence, South of Vault 101) will trade technology items for; tons of 5.56 ammo, Stimpaks, grenades, or Rad Away. Casdin's subtitles incorrectly call it ".556 ammo". Prolonged trading with the Outcasts will also eventually gain you access into Fort Independence without the residents becoming hostile.


 * Visit Canterbury Commons and invest in the weapons and armor merchants (Lucky Harith and Crow). They will then sell power armor and laser weapons. These are usually in poor condition, thus very cheap. Fast travel to Fort Independence and trade for ammunition. Sleep 48hrs, rinse and repeat. Using this method you can build up thousands of rounds of 5.56 quickly and cheaply. Additionally, Chief Gustavo of Tenpenny Towers usually has cheap Laser Rifles and Laser Pistols.


 * The Ammo Press becomes available upon the completion of the quest Free Labor. Located in The Mill of The Pitt, it converts any firearm ammo or scrap metal into any other firearm ammo--including 5.56mm!


 * Raider, Talon, and Mutant camps also stockpile 5.56mm--check the Downtown ruins and the Metro tunnels beneath it.

Ammo
Weapons using 5.56mm ammunition:
 * Assault Rifle
 * Chinese Assault Rifle
 * Xuanlong Assault Rifle
 * Infiltrator
 * Perforator

The oddity of this is that in real life, the Chinese Assault Rifle uses 7.62mm ammo, like the AK-47. This compromise may have been so that the Assault Rifle and Chinese Assault Rifle could use the same ammo.

Fallout Tactics
Weapons using 5.56mm ammunition:
 * M16A1
 * Ruger AC556F