125gr blk rounds hit harder than any 556 could hope. I would take one over 556 anyday. It also runs subs equally well in a gasser. Good luck doing that with a 556. The 556 only came about because of a change in military doctrine that favored 100 sprayed rounds vs 1 well aimed shot. The 300blk and 6.8 are both huge steps in the right direction to realizing the 308 is the best platoon level round we have.
As for the original question, just drop in a 30 cal bbl and it's a blk. No other mods required. You may need to tweak the buffer and/or spring.
As for the original question, just drop in a 30 cal bbl and it's a blk. No other mods required. You may need to tweak the buffer and/or spring.
