The only blowback 9mm handgun I've ever played with was the Astra 600 series pistols. They're kinda funky, recoil springs are horrendous, and the ergonomics leave much to be desired. But, they are very accurate and completely reliable pistols. I just can't imagine that the Makarov has enough slide mass to really pull off 9x19 and be completely safe, or reliable. If I were a betting man, I'd say the reliability problems probably stem from the slide trying to open up while the cartridge is still very tightly gripping the chamber walls; but that's just pure speculation on my part. If I were to ever own something like that, I would immediately re-barrel it back to 9x18 or perhaps .380.
