With rifled slugs in a smoothbore I like a red dot, but with the longer range, and better accuracy of sabot slugs from a rifled barrel I like a 2x-4x variable.

THE most important thing to look for in a sluggun scope, aside from durability, is eye relief. You want to be able to see through the tube without being right up near it. Bushnell makes a Banner line 2-4x with 6" of eye relief.

Keep the scope on low power for fast shots up close, and turn it up if you have time for a longer one.