Most slug guns use scopes that attach to the barrel rather than the receiver because many shotgun designs, such as the Remington 870 or 1100, have quick-change barrels. Removing the barrel would alter the zero. So, most guys who use optics such as magnified scopes or red dots on shotguns use cantilever mount slug barrels.
If you're not going to use a specific slug barrel, just use the standard bead. Otherwise, use a slug barrel, either rifled or smoothbore. Most people can get a good sight picture on a deer-sized object out to 50-100 yards, which is the limit of a smoothbore barrel firing rifled slugs, unless you've put in a ton of practice making such shots.
Keep in mind a skeet or trap barrel is like 26" to 34", so be prepared to walk in the woods with something as long as a M91/30 or a WW1 infantry rifle.