The terminal ballistic limitations of the 5.56 are well known. While it is satisfactory for many applications, it does have it's limits (please, I don't want this thread to turn into a debate about 5.56). The alternative AR rounds (the 6.8 SPC, 6.5 Grendel, and 7.62x39 being the big 3) each bring a set of ballistic advantages (and disadvantages - please, I don't what this to turn into a 6.8v6.5G flame) while also being significant improvements to 5.56 terminal ballistics. As I see it, the reason these alternatives have not caught on is equipment reliability and cost. Now that the equipment reliability is becoming less and less of a factor (mags being somewhat of a lagger) cost is, IMO what is holding them back. Question: What would it take for you to adopt one of the variant AR rounds? Also, if you are .mil or .gov, what do you think it would take for your agency to adopt one of the variant calibers?