I have one of these scopes on a muzzle loader. The Sightron S1 has great optics in my opinion, liked it better than the Nikon 1 power scope in a side by side test. I have a new Weaver V3 and would like to use it on the muzzle loader but the state I live in has a no magnification optic rule for muzzle loaders.
The Weaver K would be good as well with a little more magnification. I think a fixed power scope on an SKS would be the way to go. There was a Weaver fixed power scope listed in the classifieds just recently.