Of course I can't answer for the prior members who've posted in this Thread. I'm currently fireforming .375 Ruger cases for elkaholic's 300/375 S.I. Ruger wildcat. I've measured case head expansion as high as 0.001" per single firing thus far. As a rule of thumb, I consider anything more that 0.0005" per single shot fired to be pushing it. I'm just getting started and cannot yet comment on how many shots the Ruger .375 brass will remain useful for at 0.0005" expansion per shot fired. Probably less than 4 times before the primers are too loose.
I don't claim to be the all-knowing expert on this subject matter, but I'll share this: Long ago I read an article from a guns editor of one of the outdoor hunting magazines; Outdoor Life, Field & Stream, or Sports Afield. The article covered methods for identifying a safe maximum pressure load in one's personal rifles - for the hand loader. The author stated case head expansion just ahead of the rim on a beltless casing, and on the belt of a belted cartridge, should not exceed 0.0005" in a single firing. If it exceeded 0.0005" case head expansion with a single shot fired, then one should conclude that the maximum charge in that firearm is being exceeded. It seems this measurement is similar to another rule of thumb often mentioned. If the primer pockets remain tight for reuse for up to 5 firings, then the load is probably not excessive in that casing and firearm.
I've read a lot of additional material on this subject since that article. Some disputing the wisdom of using case head expansion to determine maximum safe pressure loads. Different case manufacturers provide casings with differing case head thicknesses and some are are more prone or less prone to case head expansion at equal pressures. However I've been hand loading for 40 years and since I read that article and began monitoring case head expansion, I've found this 0.0005" case head expansion rule-of-thumb for identifying the danger zone of maximum loads to be a useful and reasonable guideline.
I read this Thread recently and reached a personal conclusion that the loads producing the velocities posted in the 338-375 Ruger Demon surely exceed the maximum pressures that would be condoned for a factory cartridge of similar case capacity in any reloading manual. There is no other explanation. Velocity is primarily the result of case capacity and pressure, within any specific bore diameter. I don't believe there's anything magical about any particular casing design that accounts for huge differences in MV compared to other cartridges of similar capacity (volume). Case capacity, case pressure, and barrel length explain MV. There are some additional factors that play a lesser role.
Some of the inordinately high velocities posted earlier on in this Thread will surely expand primer pockets beyond further use in short order, in my opinion. Perhaps in a single firing, but almost surely within three firings per casing.
............Rich
