Dear Dave King;

I don't know if you're still around, but I thought I'd tell you my experience with this question.

20 years ago, handloaders increasingly loaded the 45 Colt cartridge to warmer levels than the old SAAMI specs for the cartridge. When this happened, we heard those handloaders were crazy. Eventually, though, the loads were standardized in 'modern firearms', and it became normalized within the shooting community. Reloading manuals included the data, all of them eventually accepting it. There are very few people interested in your question so it is unlikely the 38/55 warm loads will ever become standardized.

There is no difference in the situation regarding the 38/55 and the 375 We are talking about pretty much sraight walled cartridges that headspace on the rim. In a modern firearm, I decided to load the Marlin 336 chambered in 38/55 more robustly than the ancient SAAMI specs. It is a personal decision.

Of course there are insults waiting for one who goes off the path. All the reloading manuals tell you the two cartridges are not the same, and the 375 loadings are not safe in 38/55 rifles, making no distinction between modern rifles and ancient ones.
Thus naysayers have the documentation to back up their position. There is no point in discussing this. They'll tell you you'll blow your rifle and go straight to hades- exactly what Bowen and Linebaugh and Keith and others were told when they warmed the 45 Colt. And they'll tell you exactly what nay sayers to the warmed up loads for the 45/70 were told 20 years ago when that ancient round was reexamined. All the loading manuals at the time said not to warm the 45/70, that the rifles and brass could not take it. Well, we see where that went; there are now 3 or even 4 levels of load data for the 45/70, depending upon shooting platform.
Ken Waters is not bad company to be in today.

I would watch the brass carefully. I've experienced no problem, and have been doing this for years. I'm the quality assurance for my decision, and as I said, it is a personal decision. Your
original posts raised all the relevant points.

munk