Had some serious feed problems with a new Sub 2000 .40 cal with the multi-mag Beretta option. About every other round would not feed - the bolt would be half closed with the round at a 45 degree angle. Was using the 10 round Mec-Gar magazine that came with the rifle and tried ball, hollow-point and Hornady critical defense. All resulted in a jam as described
I was about ready to send the rifle back to Kel Tec for repairs when I decided to try loading it with the 10 round factory magazines for my Beretta 96.
Result: no jams
I took a closer look at the Mec-Gar magazines and they are shaped slightly different than the Beretta magazines.
Just some food for thought and your mileage may very.