Ironman, most of my doubles are damascus and were made before nitro powders came on the scene. Though I have shot black powder for over 50 years in muzzleloaders I just don't like it in doubles, especially when a quick second shot is needed. And black powder burns incredibly hot, uncomfortably heating the barrels in rapid shooting. So, virtually all of my shooting is with low pressure nitro powders concocted to render pressures which nearly duplicate black. This is easy to accomplish and the neat thing is you do not need to sacrifice ideal velocities--around 1150 to 1200 fps. With such loads the gun's softer metals are not overly stressed, and best of all, recoil is much gentler.
Low pressure ammunition (I prefer to call it "reasonably pressured" in contrast to the American mantra for magnum) can be bought over the counter. RST, Federal and Winchester all offer the lighter loadings that should be satisfactory.
Reloading is probably the most versatile way to go and many load recipes can be found which produce the desired velocities with under 7,000 psi. Sherman Bell wrote four articles in the Double Gun Journal about shooting low pressure nitro in these old guns and I sure recommend your beginning the journey by purchasing these copies: Volume 10, issue 2 (1999); Volume 10, issue 4 (1999); Volume 12, issue 4 (2001); and, Volume 13, issue 2 (2002). You'll also find an article on the pressure effects of shooting 2 3/4" hulls in short chambers.
Good luck in your journey!
