I have them all the time. It must be me. I once had 14 rounds of a 50 round box not fire. Even with repeated strikes with the hammer. I was shooting my CZ-100, with the 10 round mags, and had 4 not fire. I pulled the trigger 20 times then racked the slide to eject the bad round, and the primer look like all the ones the that did fire. I had them with Rem UMC (green and white box) WWB (only like 5 per 1000, oddly this is the best ammo I have ever shot), Aguila in 9mm, and 22lr, 32acp (that was the the box that had 14 duds), Fioccci 9mm (that is the one that I in the CZ-100), Wolf (had like 5-6 in a 50 round box). Now, I have never had a dud with my 50 year surplus ammo, and never had a dud with any rifle ammo (yet). Oh I can't count how many 22lr that are laying where I dumped them. Like I said, it must be me, cuz, I have them all the time, but my friends are going `wow I have never seen a dud before'. But that my life.....
PS: My 25acp, has never had a dud (also yet), and I don't shoot my 45acp to have a dud yet. But I do shoot a LOT more 9mm than anything else, like 1000's more, so the numbers are against me on that one.