Did not work for ruger american hunter stanag .300 blackout - Magpul Industries Hunter American Stock - Ruger American SA STANAG Magazine Well

After waiting 13 months to actually ship, it arrived with much fanfare, and then fizzled. Now, I love Magpul and own many, many items of theirs, but this stock with the STANAG magazine just did not work for the .300 Blackout. I have the same stock for a Rem 700 .308 that runs like a champ (5 stars), but this application was a dud.
I put together 2 sets of dummy rounds with different weight bullets to try and diagnose the problem and both attempts were failures.
Between failures to feed, being unable to open the bolt, damaged caused to the top bullet in the magazine, I gave up. If the bullet was in the right position in the magazine, I could not even open the bolt.
Yes, I could have spent time shimming the bottom metal, but I was just so disappointed with the arrangement, I returned it.
Salt to taste.