I think I am going to exchange it, I don't want to deal with a fucking tight chamber until the end of time.

The question is, are they all like this or is this a bad one?

The only case that doesn't have extraction problems is the Hornady modified case, it is .002" smaller at the base, I already have two sizing dies for this, neither will touch the brass on the Lapua cases at the base. I'm not sure small base dies even size .002" smaller.

To add, it is not the shoulder, I have bumped it back .040" farther than the Hornady modified case. Of course this fucking oddball round is nowhere to be found locally so I ordered some, be a week. That is not relevant because I don't shoot factory ammo, I just ordered it to see how it fit.

I have a Satern 24" barrel that I have not had the least bit of trouble with. It shoots my handloads and commercial Hornady ammo really nice but then I only use the once fired Hornady brass to reload. I was getting PPU ammo and it shot great also but then PPU had a recall on the stuff so I stopped using it. I use the Lee 6.5 Grendel dies so nothing special. If commercial and reloaded ammo is tight in the chamber maybe you should contact Satern and explain the problem and get a replacement barrel.

Sounds like you got an out of spec chamber, especially if this is a button rifled Grendel II barrel from Liberty/Satern/A R Stoner.   These barrels are mass produced and don't get the attention that the cut rifled Satern barrels receive but cost three times as much.

I will call them to see if this is a fluke or standard. I won't ever use factory ammo so if it fits or not isn't relevant.

If I cannot use Lapua brass, I have no interest in keeping it. 

Kinda sounds like the reamer was too worn when that barrel was chambered. Your best bet would probably to get a replacement.

Yes it is one from Brownells.

I'm returning it and have as another coming, backordered again of course.

That chamber sounds pretty tight.  I usually try to resize as little as possible and haven't had issues like that with bery many barrels.

I had a similar issue with my 18in Saturn barrel. After much frustration I found out it wasn't the barrel at all. It was the bolt that was supplied with it. After measuring I found that it was not a deep as it should be. After ordering a bolt from AA and checking head space everything has functioned beautifully. I'd look into the bolt for sure.

Yeah I measured the bolt with a depth mic, it was 0.136", the brass had a oval shiny spot where it was sticking at the base.
I don't know the method of putting in barrel extension pins but I wonder if the process could have dimpled the ID of the chamber. The shiny spot on the brass looked similar to what that would do.