Be very careful what the people behind the counter tell you. I once watched a sales person sell a woman a CVA Bobcat rifle and then told her drop two pellets down it and this kind of sabot and you should be right on. I then decided this fellow needed to be informed a little and explained the rifle really was not meant for pellets, she'd save money with loose Pyrodex RS, start with 70 grains of powder, and try some roundball or some of the T/C maxiball the store sold. I also mentioned it would be a good idea to read the manual cover to cover.

Anyway, a rifle scope works fine on the muzzleloader like Keith said, look at some of the recoil the modern rifles have. I have a Sightron S1 (rifle scope) and a Millet Buck (rifle scope) on two of my inline rifles and they work just fine. The reason a lot of shotgun scopes are suggested is because of the eye relief.

The Bushnell Banner Dusk to Dawn 1.5-4.5x32mm works great for 100 yards and under hunting. The Nikon Pro Sport 2-7x32mm is highly recommended. There are a lot of great scopes out there with good eye relief. It just depends on what you want to spend.