Yes, the 450/458 are 5.56 bolts opened up to a .308 bolt face with thin walls. From what I understand from reading, the length of the action for 5.56 guns, prevents using a larger .308 AR bolt.
The 6.8 bolt is similiar in the opening of the bolt face, but a bit thicker wall and higher pressures.
IIRC, the Beawulf uses the 7.62 x 39 bolt.
Oly is also making a .22-250 AR as well. I think we are about to see a surge of high power cartridges as the next wave of ARs.
Last edited by AH64guy; 06/21/13.
