Originally Posted by mike from philly
Ral.G. .... do you have any old magazines? The ones before the cut outs. When you hit a run of BTF, switch the mags to the old style. See if that makes a difference.
My hypothesis is that the mags are flexing just enough to interfere with the ejecting brass.
I don't have any 9mm mags without the ambi cut. That said, I was using two randomly selected mags out of the 10 I own, and both started the day cycling fine, ending the day with BTF.
Interesting idea, though.