I purchased an upper in 224 Valkyrie a couple of years ago. I had trouble with the magazines they recommended. I had to bend the feed lips to get them to work. Then I tried another brand. Same problem. Additionally, I could not get more than 10 rounds in the 15 round magazines.
I will add that I was shooting the Hornady 88 grain ELD in the factory load. The tips would break off every now and then. On another forum this was listed as a problem with the Uintah and the gas guns. I have a RRA in 224 Valkyrie and experienced tips breaking with the 88 ELD but not the Federal with the 80.5 Berger.
Anyway, I thought that the problem was fixed with the Uintah by using the PRI magazines but the last time I shot it, I experienced a few tips breaking.
I also had some concerns over the trigger combined with that upper. I tried using Hiper-Fire and the Velocity trigger that they recommended.
I'll try to explain it clearly but it would be easier to show you in person. I pull the bolt back and it cocks the hammer back. Then I move the bolt forward but not all the way. I move it far enough forward but not cam completely over to fully engage the locking lugs.
To do a safety check, I pull the trigger and hear a very faint click. It's not a loud snap like a dry fire. Then when I cam the bolt forward the hammer slams forward.
I put an empty case with a live primer in the rifle and do the above experiment. Sure enough, the primer is detonated.
Phone calls and e-mails to Uintah went unanswered.
When I didn't have any tip breakage on the 88 ELDs, they were like a laser beam in the accuracy department. I liked them so much that back when they were cheaper than Federal 223 GMM, I bought a gadzillion rounds.
I decided to give the upper away to someone that I didn't like

I told them about the magazine problems and concerns over the trigger and admonished him to avoid the 88 ELD with the Uintah.
Right now, I'm waiting for the gunsmith to finish a custom build with an Origin action in 224 Valkyire.
I got the RRA in 224 Valkyrie and really like the Federal GMM with the 80.5 Berger bullet. If you want something in the 224 Valkyrie, I recommend the RRA upper or go custom build.