If you plan on using only card wads (no plastic shot cups) with your black powder loads, I highly recommend using only bismuth. All other non-toxic shot, other than steel, contains tungsten in some form. Even if the pellet is claimed to be soft, i.e. it can be crushed, the tungsten that it contains will be abrasive to your barrel.
If you don't plan on shooting more than a hand full of rounds during a hunting season, this is probably a so what. If you plan on shooting hundreds or thousands of rounds, there is potential for erosion of your chamber and chokes.
