I would give Gunwerks a call and ask questions. Did you also buy the die set from them? If you have the thicker brass the supplied neck bushing size was also wrong for the thicker brass giving you very difficult seating as well as the improper neck clearance as I mentioned in the other post. Have you determined that you actually have the thicker brass?
Who's reamer did you use? If it was also Gunwerks I think you will be able to talk them into exchanging the brass. After all THEY missed this mistake when they sent you an incompatible setup. It is THEIR proprietary cartridge and you paid plenty of money to get it. IT SHOULD WORK. IMO If you have the thicker brass the rifle is not going to yield the accuracy with the velocity it should have.
You are not the only one who had this happen. My friend Casey, here in Tucson, had to deal with this issue after several agonizing loading and range sessions puzzling over what was wrong. Unfortunately he had his rifle built by a local gunsmith that used his own reamer so Casey never pursued a solution from Gunwerks. A mutual friend neck turned all of Casey's brass solving his issue.
If you cannot get satisfaction from Gunwerks:
This situation can be salvaged by neck turning. Unfortunately it will take some time and money. Some of the handloaders here turn necks with custom chambers and consider it part of the process.
Do you know the chamber neck dimension? Who ever used/owned the reamer should know that value. Next measure the outside diameter of several loaded rounds. The difference should be how much neck release you have. From my readings .004" (.002" per side) total difference is absolute minimum for a hunting rifle 006"(.003" per side) is better. Heck you won't have any issues if you make an even larger clearance but no need to go past .008"(.004" per side)
All that is necessary is to turn the necks for a bit more bullet release clearance. I know turning is tedious but it only has to be done once. The bushing may also have to be switched to the correct size depending on how much brass is removed.
I use the K and M system. I see they now offer a kit with a box. Very nice.
Neck Turner Kit - Complete Kits - Reloading Accessories - Accessories
As for turning them you need the mandrel for expanding the necks to fit the pilot on the turner. I used an old lyman chuck off my case trimmer which I hold in a vice to hold the brass. You may need to buy their brass holder. A bit of imperial sizing wax and an accurate measuring tool and you can turn those necks yourself.
Link from Accurate shooter on how to neck turn:
Neck-Turning Basics within AccurateShooter.com
tips on cutting:
Neck-Turning Tool Cutting Tips within AccurateShooter.com
I would like to hear what happens next. Please post things here.
I wish you the best on this issue.
Ross