What would cause this

Like a lot of people said, could be the reamer or dies. Couple things to check or try, pocket reamer to uniform primer pocket , trim the case a little to see if that helps, at least will cheaply iliminate a couple maybes. Goodluck. Sure looks like there is a rough spot on bolt face around firing pin hole.
I have a Christensen arms elr in 6.5 prc and I am getting these marks on my primers. I put a resized case and primer no powder or bullet in the chamber and the bolt is really stiff. Any ideas
So you are resizing the brass , priming it, then putting it in the chamber and getting these marks, and it is tight.? I would check the shoulder to see if it is mushroomed from the FL die. If you crushed the shoulder a little it could cause tightness on bolting. Looks like your primer sticks out too far. I would start all over and make sure you don't set the shoulder back too far and set the primer flush.
To me it looks like the primer is a spent primer that was pushed out and reseated.
I had a Christensen barrel and an action (Rem 700 before they made their own). I had to drop down below start velocities to reduce the signs you have. It was also ADG brass. In two different cartridges I am at LEAST 2 grains lower than other brass with ADG.

What velocities are you getting compared to data? I am faster in ADG with less powder.
Looks to be something on the bolt face around the firing pin hole. Almost appears to be a protrusion where the rifle was 'dry fired' many, many times which resulted in the firing pin bottoming out on the inside end of the bolt, pushing the metal around the hole forward. When the bolt is closed on the case, the excess protruding metal etches the primer as the bolt is rotated closed.
In looking at the picture. It appears to me, that the primer is not fired. The primer is still rounded and not flatten as would be shown with max or getting toward max pressure and flatten primer. I would say the primer isn't seated correctly partly, and pushing against the bolt face, and firing pin hole. The case isn't being resize correctly (Check your case length) creating pressure against the bolt faces because it's to long. He saying the bolt is hard to lift, and I am wonder if the bolt is hard to close too. If the picture was a little clearer it would help too. What I am saying is either the resizing job not being done correctly, or the brass is to long or is bad. It's being force against the bolt face. It would be hard to turn the bolt, and the bolt is turning on the case base as it's being closed and open leaving those marks.
Had almost the same thing happening even with factory ammo found the bolt face was not machined flat and had a raised ridge around the firing pin also was showing ejector marks on fired brass from factory loads called christensen and they told me the ejector marks were normal as the run match chambers (lmao) I told the guy on the phone anytime you start seeing ejector marks raised in the brass its overpressure and that the bolt closing stiff marking up primers and cutting brass off the case around the primer was not normal not sure if he thought he was talking to a complete dummy or what but your problem is almost identical to mine and the gun had to be sent back ,have seen this on more than one ridgeline over the years of guns other people owned. Just thought I would throw that out there. Try some factory ammo and see if it still does it if so I would call Christensen. Good luck.
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1 - agree with all the pressure signs comments - this shows high pressure on the brass.
2 - agree the stiff bolt closing and opening can be from couple reasons;
* headspace of brass is wrong, have you measured headspace and validated against the brass? Have you measured headspace using the​
* full length resizing? If not, high pressure load will stretch case causing hard bolt and possibly firing pin hole impingement on the primer​
* Using Redding Competition shell holders to control shoulder bump?​
* have you tried to cycle a brand new case not fired with a primer installed to see if the same effect is there? If a new case shows the same exact issue that will send you in entirely different direction for resolution.
3- agree the primer pockets could be suspect as well. Usually ADG bras pockets really don't need to be reamed but maybe these do to insure good primer seat below case base.
4 -agree the bolt face may need further evaluation, high pressure loads can alter the bolt face after repeated firings of high pressure loads.

The first thing I would do is cycle a new case right out of the bag with a primer (neck size to eliminate any issue there) to determine next step.

You beat me to saying same thing. Need a control! Trying a primed virgin piece of brass would do it. I await what happens from the OP.

I agree with JKB57 that a call to Christensen will be taxing on your patience. I got the run around with questions on one of their rifles too. At one point the guy asked who's ammo I was using. I said handloads and he immediately blurted out that would void the warranty. I laughed.