Old John, speaking of the late John Buhmiller, used to toughen up for his African rifles using a Rigby SXS .450 BPE. Cast bullets were cheap to make and Dupont BP also cheap and easily available, thus the use of the black powder rifle.

In order to increase the recoil to similar levels as the smokeless guns, he loaded his cases full of BP and 500gr. cast bullets. He also tied a block of wood between the triggers so both would go at the same time. Pulling the front trigger would set of the left barrel as well - doubling the recoil, of course. He noted this left him in fine shape for shooting the smokeless guns, such as the .505 and .450 magnums he used quite considerably.

He also noted, (as I foolishly found myself when a kid) that trying to pull both triggers at once, usually left one looking for bandades and/or stitches for the top of the second finger. The recoil drives the gun rearwards, which drives the back side of the front trigger into the top of the second finger. The result is usually a deep cut - was for me, and I had only fired a pair of 2 3/4" 1 1/2oz mag. loads while out European Hare shooting. I missed.

I realize the double pull noted in the above post was in jest, but just in case someone thought they'd try it, I mention this.