In my early career I advocated for the use of a lubricant to salvage brass which had been formed with headspace too short. I saw nothing wrong with lubricating cases for fire forming either and often did so when using blank loads to form brass. Then, one time, a customer brought in a rifle (in 280 AI) in which he had loaded some 160's, ahead of 4320 powder, and had sprayed on some aerosol lube. Everything was fine for most of the lot until one case came out with a strange dent pattern. Subsequent shots formed OK but there were marks on the shoulder. Close inspection of the chamber showed some divots at the shoulder which looked just like the sort of pitting one sees on a piston or on a cylinder head from detonation. I theorized, at the time, that the lubricant had vaporized, under pressure, and, being confined and in the presence of enough air, had detonated and damaged the shoulder surface. I ended up setting the barrel back 1/4 turn to clean up and, from that time forward, didn't recommend the use of lubricant when fireforming. I had formed hundreds of cases , lubed, with no issues up to this point but there it was. It may well be that the particular lube had a low enough flash point what it was an issue or it may simply have been a perfect storm sort of thing. This happened in the late'70's.
Of course, like most people, I loaded and formed hundreds of PPC cases by simply loading and shooting them; often at a match! I won matches while fire forming brass. The PPC was, and is, easy to form and all AI cartridges should work the same but tolerances are plainly, different for many of them. GD
