I got a whole bunch of 20 rounders as freebies when I bought my 15T. I used it once and threw them back in the safe. The mag somehow loaded two rounds at the same time. I was able to eject one round, but the other somehow got lodged between the bolt carrier and the gas tube. Keep in mind, this was a brand-new AR that I just cleaned thoroughly and lubed the night before. I took it apart and tried again, same situation. Asked the gunsmith to take a look at it, and it happened to him too. He finally tried out a PMAG and had no problems. I ended up buying the PMAGs which solved the problem, but now my gas tube is crooked.

These mags are terrible, don't waste your money.