I see that the Barnes Balistics Software is no longer available for purchase. Does anyone know of a comparable program?

Most I find for download are only for factory loaded rounds. That obviously doesn't work well with muzzleloaders.

Thanks in advance.

Not a download but this is the one I use. If you know the BC and the muzzle speed of your projectile I believe it's very accurate. It will at least get you pretty darn close.

http://handloads.com/calc/index.html

That's the one I use also Josmund. It's simple to use, doesn't require loading anything into your PC, and I've found it to be very close to my real world trajectory.