A good friend ( a now retired gunsmith) bought a Lead Sled about fifteen years ago and intended to use it for testing / sighting in heavy-recoiling customer rifles. It was on top of a tall gun safe the first time I saw it. I looked at that contraption and couldn't imagine using something like that in place of a good solid heavy rest and bags. I'm pretty sure the gunsmith had the same thought. I don't believe the Lead Sled was ever moved from its position atop the safe; likely still there today.
