Ranger and Federal pattern pretty darn close IMHO, Ranger just kicks less. It is important to remember that slugs were primarlily designed for hunting, Buck for that matter also. It is a fairly modern practice to produce HD or "Low Recoil" LEO/Military rnds. Historically and even today(Winchester especially, their stuff is the same but a different color shell) Military/MOST PD's use off the shelf ammo. WHen I got to one of my PD's I work with, they had only Remington loads, same loads as walmart carries. Ranger is availible to civies, I've seen it at basspro and lots of it at local Gun shows.
Sabot are in fact for rifled bbls, however, for training at say 15yds or less it will do fine. (had more than one student show up with all sabots)
It will work well enough at MOST HD distances as well, Its just not nade for a smooth bore but NO damage will occur is shot through a MOD or less choke.