I could use a little help in which cartridge to go with in my next AR. I plan on building it from scratch in either 6.8 SPC or 6.5 Grendel. I would be using the rifle mainly for hunting, but it would also be a zombie gun. From what I have been able to find they are about equal out to about 500 yards, which is way farther than I plan on shooting anything. Other considerations are ammo availability and cost, both factory and componants to reload. Any help is welcome and appreciated.