You have to be really careful with old guns and data. This is a pretty good example of why.
The 1885 action was designed as a black powder cartridge rifle. That in itself won't disqualify it for high pressure loads.
The Low wall version is a modified High wall. The modification was to cut off the portion of the frame directly behind the bore to ease use of smaller cartridges. The portion of the beech block that needs the most support, has none.The frame was originally forged and case hardened.
The next modification was after Smokeless powder was introduced. Instead of case hardening, the steel was heat treated. Presumably this was done to correct problems that started to show up due to the higher pressures.
Generally, when talking about converting to smokeless loads, it's the later, post 90,0000 serial numbered actions designed for the higher pressures that are advised.
Then you get into load data and max pressure data. A lot of whats out there was written pre 1970. That's an important date because prior to that time, most data was published in CUP. Every one looks back a data from P.O. Ackley and talks about him loading extremely hot loads. When you factor in the difference of measurement, CUP and piezoelectric, the loads weren't that hot.
If you look at the 357 magnum, SAAMI CUP pressure is 45,000 and Piezoelectric, currently the standard, is 35,000 psi.
Looking at data and articles written in the hay day of converting old single shots to varmint rifles, it needs to be taken on context.
Frank De Hass was a very well published writer in the 60's and his work is still respected today. He wrote an article in 1965 that was later published as a chapter in his 1969 book, Single shot rifles and actions.
He goes into detail on the Low Wall and the pressures it can handle safely. In his opinion, Factory loads of 45,000 pounds are safe in the heat treated action. The problem is, the method of arriving at that number is not stated. in 1965, it would have been common knowledge, CUP. Interestingly enough, 45,000 is SAAMI max for CUP method of testing.
In 1983, another De Haas book was published. "Mr Single shot's Gunsmith Idea's". That same 1965 article was in the new book, although revised. The 45,000 pound reference was removed, "factory 357 loads" remained. That would seem to indicate enough confusion over the original text warranted a removal, to prevent a 45,000 psi load being assumed safe.
SAAMI still lists CUP and PSI max loads for cartridges of the day. It's well worth the time when looking at old data to find out what the max pressure indicates.
A lot of people shoot antiques, I shoot a lot of them. Opinions vary greatly over what is safe and what is not. The problem is that being wrong, is often found the hard way.
Stay safe.
