Imagine 22,000 lbs of ground-up tires with all the steel and other crap removed,
ground to @ 1/8" pebbles. This is the material in the backstop of a shooting range.
There is a conservative estimate of 10,000 lbs of lead and copper to a much lesser
degree in the rubber. This isn't the first clean-out/rebuild, the last one was five
years ago. The idea is to remove all the material, separate it and reuse the rubber.
One of the ideas we've had is to float the rubber in water and skim it off. But, 1/2
of a sample amount floats, 1/3 sinks and 1/6 stays suspended. In a 1/3 cup of the
material, there was 64 grams of lead! I doubt that there is much lead in the material
above the target line. The sample was taken at the very bottom, about 5' below the
target line. They don't really want the range down for more than a week to do the
clean-out and replace the front which is 4' wide x 3/4" thick conveyor belt lengths
suspended from the ceiling and anchored to the floor and overlap by 8" and screwed
together. The conveyor belting is bulging out close to a foot in the center of each
of the ten lanes. It seems that this type of backstop is excellent for stopping
bullets and keeping the dust to a minimum.