This gas operated semi-automatic packs a bigger punch than the 5.56mm/.223models a .270 cal. 6.8mm SPC (Special Purpose Cartridge) specifically developed for the military, but now available commercially. Velocity averages a bit over 2600 FPS (with Hornady 115 Gr.V-Max), and the heavier bullet weights deliver excellent terminal energies. The 6.8 mm SPC was developed from a .30 Remington case which is shortened slightly to fit the AR15 type magazine. This is a state compliant rifle with a 10 orund magazine but due to the fatter case diameter, magazine capacity in a 30 Round AR type shell is reduced to 26 Rounds, and 6.8 specific springs and followers are used. The bolt is also different - due again to case diameter (take care not to interchange a 5.56mm/.223 bolt with a 6.8mm SPC bolt). Becaust this rifle is state compliant it has a fixed stock, 10 round mag and muzzle brake