The first thing I do with any gun and tuning is throw on a high power target scope and test loads. It becomes plainly obvious when you flinch, pull or otherwise pooch the trigger. If you are trying to zero in on the best load using the irons then move up your paper to 25 and 50 yards and you can get a better idea of when it is your error and not the ammo's. Sandbags can suffice down to 1/4 - 1/2" range at 100 no need for a sled. Maybe you really haven't settled into that rear peep yet or are "over-thinking" it? Between it and the AR's stock weld it can be a challenge for someone used to bolt gun ergonomics. It was for me.