At the range in NY that I used to belong to they built a "shoot house" for highpower rifles. You sit on one side of the brick building and fire through the building via small windows on each side. It definitely kills some of the noise, but man does it suck to have to limit yourself to an offhand window and a benchrest window. The idea was mainly conceived to keep bullets from escaping over the hill behind the range (housing development went in behind the range, who the hell thought of that braindead idea I do not know). The range is fully baffled for smallbore competitions--large wooden "sails" set up at intervals parallel to the firing points to trap any bullet trajectory that would range beyond 100 yards. Major pain to build, major pain to maintain. It kept the range alive for only another 10 years--things are looking pretty slow these days. I think it only gets used a couple of times a year now. The shoot house is used by all the hunters sighting in their deer rifles though.
I would stay away from old tires--they are bees nest magnets. I suppose you could fill them with dirt or something, but that would probably obviate the sound-deadening capabilities.