Really? What would actually happen here, the sparks would ignite the backstop, or what? Copper ammo does not generate sparks?
(I always thought it was to protect the backstop for indoor ranges since the harder metals chew it up).
I'm not sure really, it's just what I've been told by several different ranges. I know that there have been documented cases of sparks causing brush fires at outdoor ranges after striking steel, but I don't really see the threat for an indoor range. Probably some insurance reg.