I bought a case of 9mm FMJ a little over two years ago. There was 1 squib round about halfway through in a Glock 19. My roommate was shooting it at the time, pulled the trigger and noticed the light recoil. I noticed a significant reduction in report and told him to stop. I disassembled the pistol and the bullet was halfway out the barrel. Tapping the barrel on a hard surface wouldn't clear the round, nor would a cleaning rod. I took it into my local gun shop and they used a drill press to get the round out.
I know that's only one bad round, but if my roommate or another less experienced shooter had been running the mag and kept firing, it could have cost him a couple fingers or endangered his sight, or at the very least ruined the pistol. Since then I've switched to MagTech with no problems in several thousand rounds of 9mm and .45 ACP.