I could be wrong, but the 100 yard range recommendations,
probably are in reference to Foster style "rifled" slugs,
and not sabot slugs, fired from a fully rifled barrel.
In a 20 gauge, the sabots are probably in the 45 to 50
caliber range. With a good match of sabot slug, in a
fully rifled barrel, and an experienced shooter, these
are plenty lethal out to 200 yards. I have shot scoped
12 ga. shotguns, with fully rifled barrels, shooting Remington
"Copper Solids" brand sabots, out to 200 yards, and held
a 4" group. I have a custom peep on my fully rifled
shotgun, for brushy forest shooting, and that does limit
me to 100 to 150 yards, accuracy wise, but with a good
set of optics, one should be good to 200 yards, with practice.
Squeeze