You're talking about SHOT rounds. Slug and Sabot rounds have everything to do with shotguns too. The ranges for these last two are better obviously but they are still not AS accurate or long ranged as you can expect from a RIFLE. But, the different rounds make the modern shotgun a good option in lots of situations. The SMG was the favoured weapon for Urban Pacification and room sweeping but now the Automatic Shotgun has far surpassed them in everything but bulk and the ability to conceal them on your person.
should do more damage (2D6?) at close range (3"?) but only to one target while doing less damage (1D6+3?) at longer range (6"?) but with the ability of hitting more targets (anything within 1" of target?)
should provide solid armour defeating rules and damage. Say, 2D6 damage up to 12" range and all armour is halve value round down. HOWEVER, if you want to be really technical then mini-figs without armour only suffer 1D6 damage due to over penetration.
should be far more accurate and should be available for both the above shells but are far more rare. I would take both the rules above and increase all ranges by +3"
Argh! See what you've all made me do?!? This is far too rules like for Brikwars.