Again, thanks for the replies. That's why I posted here, to get a spectrum of opinions. My first thoughts when it happened, besides are my fingers still attached, were wtf went wrong? Did I have an overcharge or out of battery fire? I called my local guru/mentor and his first impression was overcharge. He has seen it a number of times, twice in one match on Glocks and reloads. BTW, he uses this load as well as it is a minimum load on Hodgdon's site. I have taken it down to 3gr but the reliability/function gets pretty sketchy on a G17 with modified springs, virtually no recoil. I took another look at the case under a magnifier and it is definatley bulged were the barrel has an unsupported chamber. To me that eliminates out of battery fire, so the only other possibility would be overcharge imho. I am usually very careful when loading, but apparently I missed one. I load on a Hornady LNL AP and have literally loaded tens of thousands of rounds with no serious issue until now. The only other issue I have ever had was a case head separation on Lapua brass in my .308 gas gun and that was brass fatigue rather than a load error. Now that was an experience! The Hornady is pretty particular as to how it runs. A small bit of spilled powder in the primer inserter slide area and you are screwed. The slide mechanism will not fully stop over the primer inserter and insertion is almost impossible. Or other times the primer does not seat fully and you can feel it in the handle. When running most types of machines, be it reloading or machine shop type stuff, the operator develops a sense of feel and you know when something is off. When either of the above happens my standard practice is to STOP, find the issue and repair it, pull all the cases off the press and start over, dumping any powder dropped back in the hopper. I can't figure out how the hell I missed this one. I went on a pre-election reloading binge so I literally have 3k+ loaded 9mm rounds to check. As luck should have it I was looking at the new Dillon 1100 a couple of days ago but the Democrat chicom virus has severely hit my wallet. Looks like a long day of checking loaded cartridges...
CR