Been wanting t play with this theory for years myself, and have yet to actually do it [beeep]. Here in PA, we have a number of seasons overlap, and I have 2 combo guns in 222/12 ga that I would like to work up small game and longer range rounds for turkeys and such in the fall.
Reduced loads, Blue dot loads, fast powder/slow velocity loads all lead this way. In bullets, cast (as mentioned above), fmj's, reversed bullets (yes, it's actually been tried to load an inexpensive fmj bullet backwards with a "reduced" load to increase frontal area for shorter ranges - not sure on this one!), heavier duty bullets (thicker jacket/low expansion), etc. all have attractions and detractors. In general, find a load listed in the manuals as safe, slower than normal for cartridge in speed is generally desirable, and load with a low expansion bullet. Load within safe book parameters for accuracy.
Generally, if you can find an inexpensive, yet accurate bullet, in your gun, that is not plastic tipped or hollow pointed, slow it down to maybe 22 mag velocities, and get accuracy, you got it. FMJ's should act similar to cast bullets in .22 cal's for very small game such as squirrels and rabbits. That said, I still think gray squirrels are one of the toughest animals on the planet, pound for pound! Sometimes they just don't realize that they are dead yet. The points can be reworked with a meplat device if desired.
I believe a bunch of the guys on castboolits.com have played with this.
Now let us know what you find out.