It's certainly possible the rifle has a problem, but it's a fact, that switching to a large frame AR will require changing technique at the firing line. In general:
1. Load the tripod firmly
2. Maintain a firm but not crushing cheek weld and shoulder pressure
3. Extra lite touch on the grip - I barely touch mine
4. Focus on keeping your trigger pressure in a straight line back down the rifle.
5. Think linear - all pressure straight back.
For me, the grip pressure is the biggie. AR10 format guns have a lot of reciprocating mass. Lateral pressure on the grip (steering), or shooting it like a bolt gun (overall lighter grip), are the most common problems in my experience.
Also, run the gas system at the minimum workable gas setting, and adjust gas every time you change loads, especially if bullet weight changes. Stay low.
Also, don't expect factory ammo to produce much better than inch sized groups at best. Yeah, sometimes you'll get a barrel that'll shoot everything, but more often the gun is going to like one type of bullet and loading better than the rest, so to get down to sub size, you'll need to do some quality reloading.
That being said, the DPMS clone guns are slammy as hell, and AR10's without a adjustable gas port are not suited to accurate shooting. JP's low mass system helps with this. I shoot a Savage MSR-10 for this reason - smaller receiver, smaller BCG, excellent gas system - way less recip mass to deal with.
