Recently at a machine gun shoot, there were numerous failure to extract/double feeds through multiple factory, PMAGS, and BETA 100 round glock drum when shooting full auto. Fired casing wouldn't extract from barrel followed by another live round trying to feed after about 10 round full auto bursts each. I don't believe it's the magazines since they were all similar failures and all mags have good track records (fired about 10 burst and had to drop mags/drum and cycle out double feeds). The system was a glock 19 all factory parts gen 3 less than 500 rounds through it. There was zero "limp-wristing" for sure and it wasn't the post sample sear because it was also tested on another factory gen 3 glock 17. The only thing I can think of was the ammo????????? .....The ammo being used was federal aluminium from Walmart I believe (or some other factory aluminum brand at Walmart for sure if not federal brand). Is the ammo the culprit and if so, what/which types of ammo is reliable to run full auto successfully on mag dumps from others who have had reliable full auto shoots?