I just had something nasty happen with my Makarov and Hornandy JHP. Of 16, 3 to 4 Hornandy Custom JHPs, in 9x18, must have blown their primers or something. On each occurance, burnt powder and gas was vented backward, through the firing pin hole, and into my face (nothing my glasses wouldn't stop, though). Also, they wouldn't lock the slide back on the last round, but I think I'll attribute that to the lost pressure. Finally, after about the second incident, I racked the slide to inspect the fresh cartridge and the mouth of the hollowpoint had been smashed and generally ovalized during chambering.
I can't blame the gun because I then ran 50 rounds of Fiocchi 9x18 JHP and then 100 rounds of Norinco FMJ through it without a single glitch.
Thought someone might like to know.