XM-8

Caliber: 5.56x45 mm NATO
Action: Gas operated, rotating bolt
Overall length: 838 mm in basic configuration, butt extended
Barrel length: 318 mm in basic configuration; also 229 mm in Compact and 508 mm in Sharpshooter and SAW versions
Weight: 2.659 kg empty in basic configuration
Rate of fire: ~ 750 rounds per minute
Magazine capacity: 30 rounds (STANAG) or 100-rounds double drum in Automatic Rifle/SAW role

referance:
http://world.guns.ru/assault/as61-e.htm