I have a sig 556 SBR with a 10 inch barrel and a surefire can. What weight bullet will have the best penetration and nock down power within the max accuret range (about 0-200 meters)? I have a 14.5 inch Colt 6921 that I want to run an ACOG TA01NSN on. What round will run most reliably out to 600 meters and actually kill something at that distance? I also want to run my surefire can on this rifle but I need to get another flashider mount. What grain should I be looking at? Im pretty sure I need a specific grain for the ACOG.