Saw one in a match, 300 H&H magnum shooting reloads. Primer went off but powder did not ignite, bullet was stuck in the barrel and had to be removed on the line in the middle of a thousand yard string. Old boy was good. He cleared it and went back to shooting, only missed shooting 3 rounds out of the 20 required and he was not low man on the score board. If it had been me I would have gone to pieces back then, (1972), today I would shrug my shoulders, just another day on the range.
Only squib from a combat weapon was on our 5"x54 aboard the Farragut. Round stuck half way down the barrel and it was an HE round. Getting that out was interesting, especially for the seaman who carried the round in his arms down the starboard side of the ship in order to dump it off the fantail. Seconds after dumping it the shell detonated.
Not a squib but worse. The DE behind us in the north Atlantic fired a 4"x50 and the shell exploded approximately 50' from the muzzle of the gun spraying the ship with shrapnel. They had loaded up at the same New York ammo dump we did before we deployed. They got bum ammo and we got bum wings for our missiles.
That was an exciting 3 days, 3 missiles launched, 3 missiles lost, one back tracked and flew between the 2 stacks on the ship before hitting the water. We would launch and the wings were falling off due to a bad locking mechanism. They were blaming the missile house boys but they were innocent. Good thing we weren't going into a shooting situation because our fangs were pulled and our toenails clipped to the quick.