Is your bolt carrier clearing the top loaded round in the magazine? Meaning does the carrier go far enough to the rear that it picks up the next piece of brass by the head of the case? You said it was slamming into the shoulder of the case so we could gather that the bolt is not going all the way to the rear and pushing the next round by the head. This would lead me to think you are in fact not getting enough gas pressure to move the carrier all the way to the rear, but I'm not convinced it is because you do not have enough powder in the case. I would check the bolt carrier, gas key, gas tube, and gas block hole. You can increase chamber pressure and gas flow by adding more powder, but you should ensure everything else is in order first.
Thanks for the response
I don't think it is going back to the head. The mechanicals are fine with the gun. It is basically brand new with only 1,000 rounds throogh it. The last batch of ammo was fine just started with this one. So I am going to try throwing a bigger charge and see if that works.