DPMS production barrel need to be broken in before they settle in/run their finest.   Not only the bore unifying, but the chamber walls and throat edge de-burring/unifying as well.  Reloaded ammo problem could be as simple as the round loaded too long (bullet ogive embedment at loading), case left too long after trim (end of case/chamber end cut binding on loading/ignition), of just the reload too hot for the barrel.

Now back to the rings, Given that I will dam near do everything I can to make my DCM rifle unlock as late as possible (read less case ejection distance, and latter carrier movement, and even a chance for my higher barrel residual working pressures caused by slower burning powders to drop more residual working barrel pressure before unlock), I have even gone to point of using my worst worn-out rings from the road hard and abused service gear in the DCM rigs.

The McFarland rings will break -in in time (you have at least 200 round until the bore rifling unifies anyway), but do remember with slower gun powders, you will have higher residual barrel pressures at unlock, so is rings that may seal off better and allow the bolt to unlock early/during higher barrel pressures when the case is more pressure bound to the chamber wall such a good thing?

Until the barrel settles in (few hundred rounds), don't even try to work up match loads.

Just go short line (200) and work on your technique using standard 55/62gr loads to break the barrel in.  Then once everything has mated/broken in, you can start working on your 200/300/600 yard loads.

P.S. You need to know your Max OAL of each Ogive bullet design for kiss that you will be using, and work back from there, instead of just trusting the Max mag allowed length thinking that you are short of kissing the lands.

With the amount of ammo that Black hills is now producing, they are off the reservation in regards to using canister type powders.

You might want to ask over in Reloading if anyone has found a canister powder/primer/case/ and bullet that is very close to what they are achieving.
Note: I have already developed the 223 loads that I have been using for years (got to love a local barrel supplier that can duplicate custom barrels at demand), and have been speeding the free time developing loads for the new NM Garand and NM M1a.

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On a side note, I just gave up on a Boyd M1a fully inlet’d type 2 lam stock (canceled the order after waiting 5 months on a custom stock promised 4 months ago), and just settled (going to miss the oversize pistol grip section) on a Type 1 Nutmeg that should show up at the house for me going on holiday in a few weeks.  If I promised that I would get together with anyone during this time to work on your rig, it isn't going to happen since I got just enough time to get the stock/action glassed in/glued, and get to the reloading bench/range to fine tune loads before heading back out on the road.

Note: If anyone needs a lam Pepper rear hand guard for an M1a, drop me an IM. It’s been sitting on the bench for months now, and has become nothing more than a boil on my ass/reminder of just another project that should have been completed long ago (read this is the second rifle that has taken me over a year to complete due to waiting on parts/out sourcing work/getting the time to put it together).