The "local" shop I do my shooting at makes a KILLING on indoor shooting... He runs a 12 week league with 40 some guys plus MANY guys who shoot it not in the league (more non leaguers than leaguers)... 3D is thurs-sun... He has another paper animal league mon-wed with quite a few guys shooting it.... Not sure on the numbers though....

His range is almost always busy.....

*Edit* with the heavy shooting on his 3d targets, he still only replaces the cores once per year.... They do have 2 sides and all He has 15 targets... you shoot each one twice for 30 shots.