Doodle, welcome to the Forum. I am guessing your DPMS is a 1 in 10 barrel twist. That is optimised for 168 or 175 grain bullets. I woud buy a couple of boxes of each, forego the morning coffee, or at least keep it to one cup, and see what works best. Matt is giving you good advice. Good ammo does make a difference. A lot of the mil surp is destined for machine guns, where precision isn't that important. If you can find some Lake City M118LR, that is military sniper rifle ammo, and roughly equivalent to Federal 175 gr Gold Medal Match. Good stuff. Good groups are a combination of good equipment, good ammo, and most importantly, good consistent technique. If and when you start reloading, you can build a "ladder" where you fine tune a load to your particular rifles nuances. That is when really good accuracy begins.