I must admit, I am quite surprised to read that someone has the same idea that I've been harboring for some years. I am seriously thinking of doing exactly this when we eventually move (hopefully to lot with more land that we have now in a subdivision).
I envision a full basement, with one section walled off into a small shooting room with a shooting bench, a table for cleaning guns and reloading equipment, etc. A tunnel comprised of concrete cylinder sections (36" probably, perhaps 48"). Ideally, at least a 50 yard run with an I-beam to act as a track for a target carriage. Run a few lights along the top, with heavy steel to protect them from shots. Rig a simple carriage (maybe a cable running to pulleys on each end) to run to the end and bring the target back. A ventilator fan at the target end would pull smoke and gases down the tube and out to the surface.
I guess great minds DO think alike...
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