I was using my Lee Pro 1000, the same one I have been using for about 25 years. Not that it is the fault of the equipment, especially since I was using Federal primers, which are known to be temperamental, and Lee specifically says not to use them. With that said, I was burning off the last of them from when I bought them during the primer shortage a few years back. Federals were all I could get at the time, and I already loaded the other 5500 without incident. I just wanted to share what was happening, what caused it, and the damage to the press for general information. I was using mixed brass, the round in question was a lightly crimped Winchester. It looks like the primer caught on the ridge in the pocket and allowed the primer to seat except for the side that caught on the ridge. It required slightly more force to "seat" but not much more than a tight primer pocket would. It detonated under slow progressive pressure, not an abrupt impact...which I found as a surprise since a couple were crushed sideways earlier in the day without any excitement. Two other primers had a sympathetic detonation. The primer chute was shredded, but the primer cups fell directly down. The primer tray was full, it looks like the plastic giving way prevented additional explosions. I did have to pick up several unexploded primers. The hopper just fell straight down. Here is what is left of the trough, along with the culprit and empty primer cups. I was wearing glasses, but didn't get hit with any flying debris. Most of that went backwards, I have no idea where the anvils went, but they should have went straight up, because they were horizontal when they went bang. It was loud, obviously. Total damage will be a new chute, which will be $4+ shipping. I got lucky, but it also looks like the design was well thought out. If that primer chute had been metal, I think I would have had a lot more drama. The plastic shattered and sent all shrapnel (except presumably the anvils) away from me. So wear your glasses, and consider following the directions if the manufacturer says to only use certain primers. (Currently CCI and Remington, my old manuals say Winchester and CCI.) I have only heard about Federals going bang in Pro 1000s. And of course now I can't say that I have been using Federal primers for 20+ years without a problem.