Take a look at this:

http://www.champlinarms.com/gundetail.cfm?id=1385

This would really make a nice set up. A delux grade cased with a set of 20 ga barrels as well. Another $500 for re-chambering and you've got a nice double rifle, and a shotgun as well.

The hammers are no drawback to stopping a charge. Both barrels are cocked before the fight starts. After the chambers are reloaded both hammers are cocked again. The Pedersoli has rebounding hammers, and is the safest double rifle to carry loaded. The hammerless double is cocked all the time if loaded, with nothing but a little button holding the strikers back, but because you can't redily see it is cocked, one doesn't worry about it. If a hammer rifle is cocked, it can be seen from a distance!