I've always used the cheap polymer 20 round Canadian Military mags in both of my .300 Blk out AR-15's. Never had a malfunction but I've only shot factory ammo in my guns. I'd try a different mag, first.
"Allways speak the truth and you will never have to remember what you said before..." Sam Houston
Texans, "We say Grace, We Say Mam, If You Don't Like it, We Don't Give a Damn!"
~Molɔ̀ːn Labé Skýla~
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