Different powders burn at different rates and, thus, produce different peak pressures and burning curves. Smokeless powders slower than Blue Dot or 2400 will produce lower peak pressures than black powder for the same velocity, all other things being equal. What this means, contrary to many gun writers, is that certain smokeless powders are actually safer to use in black powder guns than black powder is. Powders faster than Blue Dot/2400 produce a higher pressure spike than black powder, with the Blue Dot/2400 producing a peak pressure similar to black powder, for the same velocity and all othe things being equal. For this reason, if a fellow is going to use Unique in an old pistol, he needs to understand that the peak pressure of Unique is much higher than black powder for the same velocity and all other things being equal. Therefore, he needs to decrease the muzzle velocity accordingly. Trail Boss is even worse.
For the 44 Russian, I use 12.5 grains of Accurate 5744 under a 256 grain cast Elmer Keith bullet for and average velocity of 780 fps. Recently, I was shooting at a target tacked to a hard, dry cedar tree 25 yards away that was about 7" thick. This load was putting the cast bullets right through the tree. When I first started using this load in my S&W New Model #3, I began to measure the distance from the forcing cone to the back of the frame to the nearest half thou. I eventually quit because there was no measureable change after a few hundred rounds.
In general, the pistol load charts today seem to go by the fast-powder-in-tiny-amounts strategy. You don't want this for antique pistols. I go by the slow-powder-in-large-case-filling-amounts strategy, for low peak pressures.
Too high a pressure for the same velocity will blow your cylinder but not stretch the frame. A velocity higher than BP, even if the pressure is fine, may begin to stretch your frame. You must both keep the pressure at or below BP pressures by using powder slower than 2400 and you must also keep your bullet momentum at or below original specs. Bullet momentum = weight x velocity. You do need to Chrono your loads when you are developing them to know where you are.
I'll soon be developing a smokeless load for the 45 Schofield.
