Caspian;
First of all, no, the backstrap will not bend under recoil. Some of the pistols that have totally brass frames have been known to have longevity problems. Stick with a pistol that has a steel frame and the brass grip frame will not matter at all.
Velocities are less a consideration with a cap and ball pistol than they are with a centerfire. You don't need a certain muzzle velocity to achieve deformation of the ball since the ball is pure lead and will deform at fairly low velocities. Second, a true ball has a different striking surface than does a bullet. Its face is more blunt and it imparts a greater shock than a projectile that has a more pronounced ogive.
I shoot both .44 and .36 caliber pistols from Cabela's and I can tell you a cap and ball pistol is as accurate as any other practial sidearm at reasonable ranges. I have a .44 target model that will shoot 2" groups at 25 yards and an 1860 .44 model that will stay inside 3" at the same range. I have a .36 Navy that shows promise, but I haven't worked with it much yet.
Lyman publishes a black powder handbook that lists loads and velocities. I just purchased a chronograph a week or two ago, and have not tried it yet, but I expect the .36 to give me an honest 900 fps with a standard load of 25 grains of FFFg. Just to let you know about their use for hunting, I took a red fox last fall with the .36 at about 10 to 15 yards. The ball penetrated the chest through and through. Now a fox isn't much larger than a good sized cat, but the wound was more impressive than I'd expected.
Cap and ball revolvers are a shooting discipline unto themselves. They are more fun than you'd expect, and one cannot really know what it was like for settlers who staked their fortune on a westward dream in the post Civil War era, unless they have really come to know the cap and ball revolver.
Regards;
Dan C
