I've tried to stay out of this; because there are quite a few posters on here with greater (orders of magnitude greater) knowledge and experience than I posess on the subject matter. However, there are those whose comments make me feel positively brilliant!
grxy said:
Rockwell testing the metal gun parts could give an idea of the strength.
Unfortunately to perform the Rockwell test they usually grind off some
of the metal to get beneath any case hardened layers which would ruin
the appearance of the gun.
To say nothing of weakening the part being tested - Proof tests are designed to test
the entire part or assembly (in this case the cylinder/barrel/frame); not just the part left-over after "preparation" for Rockwell testing.
For the OP: I have the Pietta steel-framed version of your Remington, and I have over-charged it with a blackpowder substitute, but
never behind a lead ball. This was only when convinced to work with a "re-enactment" group; and the only thing that kept powder in the chambers was a thin little overpowder wad, which would be long gone down the barrel before any significant pressure could build in the chambers. Smoke and noise only.
If I want "Magnum" loads in a revolver, I have a functioning Smith & Wesson Model 629 and Magnum rounds. Reading the posts on this thread and studying the links covered in the posts; with that 629 I would be reluctant to load up cartridges with the
BP charges you have mentioned.
I'll admit that my greatest concern would be the front sight -out on the end of it's 4" barrel- contacting my forehead and the copious blood-letting that painful personal experience (with commercially produced cartridges from a well-respected manufacturer) has shown me would ensue.
And purely non-scientific empirical data (no chronographs or strain guages) have proven to me that, at 10-15 yards, the steel "spinners" on my targets spin just as much and react just as violently to 35 grains of Hogdon Pyrodex behind a .454" roundball in my 7.5" -barrelled Pietta. And that is in fact 5 grains GREATER than the charge that seems to be the most precise for my Remington.
I have to add my advice to others who have stated that you're headed for a sorrowful end result; and I hope you think of your family before continuing on this track.
But your country, like mine, is semi-"free"... for a little while longer, anyway.