G, Yes, Nikon does make a scope specifically for muzzleloaders, as Home said, it is called the Omega. I have one on my T/C .50 and it is very impressive especially with the BDC reticle that allows you really reach out past 100 yards. I have shot mine at the range to 200 yards and grouped 3 inches. I have a couple of friends who use the Nikon ProStaff Series with the BDC Reticle on their ML's as well. I would encourage you to take a good look at the BDC reticle as it will definitely help make you a more accurate shooter.
Also, make sure you check out Nikon's Spot On Ballistic Web-site. It has ballistics for ML's and will give you accurate distances for your BDC Reticle.
Drop me a note if you have any questions.
Guy's thanks for all the great comments on our scopes.
I've only been shooting a muzzleloader for 14 months but sure wish I had started years ago.

http://i1216.photobucket.com/albums/...940/C50cal.jpg