The last two posters missed the part about case length limitation set at 1.625".
Also, thanks to spaniel for the tip on that 358 bfg. I had previously noticed the wssm cases being just barely longer than our limit, and thought it would be a good idea to shorten one and neck it up. It didn't seem financially feasible for an individual to come up with equipment to produce a round like that though. It's nice to see someone already did the work.
Another option is a long-barreled handgun. Cartridge restrictions for handguns are that it must fire a bullet at least .243" diameter, and have a case length of at least 1.16"; with no maximum case length set. The barrel length isn't really specified or restricted either, except that it must be at least 4". There are a couple of bolt action handguns available with (I think) 14"-16" barrels and chambered in true rifle cartridges. With a good bipod and scope, that would probably be the best bet for a long range setup that's legal in Indiana.