I just put together a nice 24" 224 Valkyrie upper that I'm excited to shoot, but I'm having a really hard time finding reliable magazines. So far I have tried with limited to zero success:

-Duramag: best so far, have to down load the 10-rd to 7
-AR Stoner: very poor, 25-rd didn't feed or lock the bolt open, 15-rd have to be down loaded to 8 to feed
-ASC: 15-rd mag, total failure, rounds just dive straight into the receiver and don't engage feed ramps.

I have some PRI ordered, will report back later. But ~$40 a mag, for 10-rd capacity, that HURTS.

Has anyone else had similar results? What are some magazines that you've had success with in 224 Valkyrie?

I used a micrometer and found my lower with the highest magazine shelf, just to be sure I wasn't experiencing a failure from "tolerance stacking"

I also was sure to use an upper receiver with matching M4 feed ramps, I'm using a 24" Faxon SS Nitride 5R barrel cut for M4 ramps. I've visually and tactile confirmed the ramps transition smoothly.

I use ASC Grendel mags in mine with zero issues.  I haven't tried anything else.

Greg

PRI has been good.  Unimag appears to be good, but I've not had enough range time with them to provide an actual recommendation.

What length gas tube?

I’ve been using the ASC mags in my 3 224Valkyrie builds. No issues with feeding once I had the gas system tuned.

Rifle length. The issue isn't just feeding when fired, I can't get rounds to even chamber from a locked bolt.

So I built a .224 with spare parts and frankensteined it together after finding some really good deals at PSA in Columbia last year and I have used two ASC mags, 10 rounders.  I have never had an issue yet (aside from the issue described below) with the weapon with feeding.  I have not used anything higher in capacity because I wanted the smaller mags for longer range shooting.  I also have a 6.5 Grendel and use same 10 round size mags and never had an issue.  Perhaps its in the higher capacity mags that could possibly have an issue with your build?  Something else i encountered was the initial lower receiver I had, had an issue with something either the BCG or the charging handle having dragging issues with the bcg itself.  The bcg wasn't going fully forward and when I pulled the charging handle to the rear it would get more resistant and kinda "stick" per say.  I had feeding issues from that particular issue and i believe it was a tolerance thing from a diff manufacture of receivers.  I swapped the upper to another lower and zero issues, functions perfect and mags work perfect.  Oh and mine has a 20" barrel with a rifle length gas tube.

PRI is best.

To everyone having good luck with ASC mags, if you have a mag you'd trade for my 15 round one, let me know. So far I've had my best luck with the duramag 10 rounders.