I shoot a few practice stages (bullseye) last night at our clubs indoor range and there were signs everywhere stating no FMJ rounds. Now I was shooting lead .22lr my bullseye rounds, but I got to thinking is a FMJ round really that much harder on a indoor backstop than a lead bullet? From what I have observed in the pin league, both lead and FMJ seem to have the same impact on the bowling pins. With such a thin layer of copper, I have a hard time understanding how this could damage the backstop.