I've been working on a 9mm load using a powder I don't normally use in this caliber since what I usually use has been hard to get.
I've been using 700X in 45 Colt, 45 ACP, and .38 Special. It seems less than ideal for 9mm but I figured a light load should be fine. I worked up a nice light load in my old HP clone (.358" barrel, slugged and measured with a micrometer):
125gr cast TC bullet, sized to .359", seated to 1.100" OAL, 3.5gr 700X. Velocity around 1000fps. Nice moderate load.
I then thought I'd try them in my other old HP. It has a replacement barrel that slugs at .355" (original barrel was dark), but the rounds dropped right into the chamber without resistance so I figured they should be fine.
Wrong, apparently. They shot and functioned fine, but the empty brass shows signs of what appear to be excessive pressure; the primers are flattened and even the headstamps looks flattened. I deprimed one and tried a new primer- it seated with minimal pressure so the pocket was definitely stretched a little.
I'm very particular with setting up my scale and powder measure, and check powder levels before seating bullets, so I'm confident that there are no problems there.
So, the bullet and round fit the chamber fine, but the bullet was oversize for the bore by about .004". Could this turn a light load into a dangerous one, with a fast powder like 700X, or is it likely to be something else?
I had another load using HS6, loaded a little hotter but still moderate, and using the same .359" bullets, that seems to work fine on both guns. Pressure this high on the 700X loads is a little scary and I'm a bit embarrassed about it, but any ideas?