The total malfunction count in my M&P9 went from 1 to 10 in the space of one magazine last weekend.
On the way to the Sooper Seekrit Range Location, I asked my hosts to swing by Wally World so I could grab some nine and .22, in order that I not be a complete mooch all weekend. The Wal-Mart in Española, NM was well stocked with deuce-deuce, but I bought the last fifty-rounder of 9mm Remington FMJ they had in the store, and supplemented it with a lone box of TulAmmo.
Ugh.
I don't know what they use on those steel cases, but it caused enough stiction against the other cartridges and the walls of the mag tube itself that the column of rounds would bind in the magazine, allowing the top rounds to rattle loosely.
At first, I was ready to blame the magazine, and borrowed a silver Sharpie to draw the Frownie Face of Disappointment on the baseplate, when, Lo! I ran out of TulAmmo and went back to shooting borrowed Winchester and Federal and the problem went away!
Every time I violate my rule of only using decadent Western Capitalist ammunition in decadent Western Capitalist guns, I get reminded why I do it that way in the first place.