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 Picking up the Trail it becomes much more available as enemies start carrying Assault Rifles in place of Hunting Rifles.

Equipment

 * "WHERE'S THE AMMO?" One of the hardest things to cope with in Fallout3 is the general lack of ammo. Even with the Scrounger perk and weapons merchants, its hard to get enough. Well thank heavens there's a solution! For 5.56 ammo anyway (Assault Rifle ammo). Brotherhood Outcast Casdin who's found at Fort Independence (nearly due south of vault 101) is friendly and with a little chat will allow you to turn in laser/plasma type weapons and your spare power armors for tons of 5.56 ammo, stimps, frags, or Radx.
 * Note: After you've visited Canterbury Commons and invested in the weapons and armor merchants (Lucky Harith and Crow) will start selling power armors and laser weapons which you can buy cheaply (as they're usually nearly broken) map hop to Fort Independence and swap them. Sleep 48hrs, rinse and repeat. Build up thousands of rounds of .556 quickly and cheaply. Additionally, if you've made it out there, Chief Gustavo of Tenpenny Towers can also be hit up for cheap laser rifles and pistols too.

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

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