Looking for recommendations for .223/5.56 SD ammo for a 1:9 twist barrel. Probably 69gr would be best? I like Cor-bon's stuff but it's very pricey (not sure they even make anything in 69gr). I want something with reliable expansion/fragmentation as I'm not concerned with punching through plate steel, etc. Also, the rule of thumb for testing ammo in a pistol is 200 rounds. What about with an AR? How many ball rounds would you put through a new AR first to verify basic functioning of the gun before testing the SD ammo?