13th months later, did you figure it out? I have a White Oak upper that doesn't like to feed right with a duramag, feeds a little better with a PRI but won't lock bolt back on last shot and after a while starts to show the same symptoms of the duramag (bolt rides on top of round that it's supposed to be loading). It appears to be slightly undergassed but not horribly, has a +1 rifle length tube I think, and non-adjustable gas block. Recently I watched some couple year old video from some youtube reloading guy who said he had best luck with AR-Stoner magazines in his 224 Valk. I bought a couple and only taken them out twice, only been loading 5 rounds at a time. But so far these AR-Stoner 10-round magazines seem to lock the bolt back and stripping rounds fine for 80-90 rounds (then starts to have issues, assumedly because the rifle is dirty, but haven't played around enough yet). It doesn't appear that Wolff makes extra power 10-round magazine springs, so I might try to cut down a 15-round spring for the duramag and PRI to see if that helps. The body of the duramag has much better looking spot welds, and the PRI just seems like a better magazine, I'm just getting feeding issues and bolt hold back issues with them. I haven't tried any of the higher capacity magazines I bought years ago when I first put the rifle together and let it collect dust for 3 years.
I should also say I also shot some really hot loads, up to 0.2 over list, but it didn't help and ejector marks stopped me short of continuing. The last rounds I fired were launching the 88gr ELD-M's at 2850. That brass went in the trash.