I haven't looked into the specifics for the reasons, but you can imagine it has to do with population density and how far a rifle bullet will travel.
Shotgun slugs are considered "short range" flying objects.
Bullets from pistols are considered "short range" flying objects.
Handgun cartridges fired from rifles are considered "short range" flying objects.
Round balls fired from muzzle loaders are considered "short range" flying objects.
That may have been true when shot gun slugs were first invented...but then came the 3" magnum, then came the sabot and the rifled barrel and these 1 oz slugs travel a looooong ways. Sorta like bullets from rifles.
That may have been true when muzzle loaders used patched round balls...but then came the in-line muzzle loader, the 209 shotgun shell primer ignition system, the BP pellets, the sabotted bullets and the belted bullets and these things travel a long ways.
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IL isn't too much different from IN. No rifles though.
I'm all set w/ my T/C Contender in 357 max, 12 ga shotgun, and 54 cal muzzle loader.
Rifles stay home....'cause they can shoot reeeeeaaaaly far...and that's bad.