Reading this makes you think before you do something stupid that will follow you for the rest of your life.LOL
I was in Illinois some years back. I was going to buy a disabled friend a muzzleloader he couldn't afford and had been wanting one for as long as I can remember.When we went to pay for it the salesman pulls out a 4473 form.I said this is a BP rifle. He said I know what it is.Then he tells us doesn't matter in IL you have to fill the 4473 out.So I'm sure in IL a muzzleloader would be considered a firearm.
Actually I think when it comes to a Felon anything that shoots a projectile by some type of powder would be considered a firearm.

I live in NC now and they apparently have a thing against crossbows.There's restrictions in catalogs that they can't ship to NC. Go figure.