I had an interesting email conversation with the Shuttleworth’s some years ago about the strength of their action. I wanted to do full power loads with basically a “modernized” rimmed Mauser cartridge. 444 Marlin necked down to 6.5 mm and 145 grain bullets with a 40 degree shoulder.

The consensus was no problem, we were discussing pressures in the range of 55-60,000. 

At that time they had never proofed one of their rifles and sounded like they had no intention to ever do so. Kind of a, the more you know, the more liability you might have type of statement.

I was told that a fair number of their rifles had been proof tested by customers over the years. Some with some very scary tales of double charges or wrong powder used. I think some of the calculated pressures were in the 90,000+psi range. No loss of an action or limb. It was an interesting exchange.

There was a certain amount confidence in their product, combined with a “let us know how that works out for you” message in the conversation that left me feeling like I might be pushing the limits. The project is in that someday I’ll do it list. 

Consider that the Miroku high walls are chambered in more than a couple magnum rounds and I think it’s safe to say the action designs are strong. 

The question on old iron is integrity, corrosion and fatigue. I shoot enough old iron to know that most failures, can’t be predicted. One day you just find a crack, if you’re lucky. If you’re not lucky the crack finds you. 

Sorry, no hard numbers, but hope it inspires some thought.

I would buy a modern rifle if I wanted a .375 Winchester. I would stick to traditional calibers in my 44 1/2, .38-55, .32.40, 25-35, 30-30, and maybe.219 zipper would be my choices.
I know that some 44 1/2’s were built in 30-40, and .25 krag, and .225 Winchester, but I think those calibers are pushing it a bit.

S99VG wrote on Jul 13^th, 2021 at 1:20am:

If this is just for playing around, it might make sense, if it is to compete, it’s probably wasted effort. It would depend on the rules of the competition. 

To take advantage of higher pressure, you would be shooting gas checks, coated, jacketed or copper solids. When you get to the heavier bullets generally used for long distance, the velocity gap narrows quickly between the two cartridges.

There is a point where the action is stronger than the speed you can push a plain lead bullet, if that’s the goal.

I have a 25 Krag barrel by CPA I bought here a year or so ago that I'm not gonna do anything with. if you are interested pm me.
It comes with dies, brass and form dies as well as an unfinished forum.
It's a 28" round barrel IIRC.
barrel is a 1 in 10 Douglas.

I had plans for this barrel but since bought a complete gun with 3 barrels.

I would think that about as far out as a black powder target rifle (BPCR Silhouette) that you could reasonably get with the 44 1/2 is a fast twist 38-55 like Pedersoli makes for the HighWall. This would get you to 500 meters. Probably should use the original longer length brass for just a little extra powder room. The 38-50 Remington Hepburn would be quite similar with the added effort of forming brass from 30-40 Krag. I shoot a 38-50 CPA in BPCR and keep my 38-55 Highwall for 200 yards.

George Nonte in "Modern Hand Loading," 1972, groups the 44 1/2 Stevens right up there with the  High Wall, Sharps Borchardt, and Remington Hepburn.

Frank de Haas,  "Single Shot Rifles and Actions,"  1969,  says, "with a properly altered firing pin, will safely handle many cartridges that develope up to 50,000pounds per square inch."  He goes on to state that the limiting factor, as mentioned already, is the diameter of the barrel shank.  He does limit it to the 30-30 base cases.

George

The hammer on an original 441/2 can be replaced with the speed hammer from CPA. It having a much lower hammer spur that is also a big benefit for being able to use a mechanical breech seater that will now very easily clear the hammer spur.