Sac
Were I a LEO local to the scene, I cannot imagine not checking nearby firing ranges. There is probably only a small number of them relative to the total number of businesses so I would imagine that the investigation potential payoff to cost ratio would be fairly high, and if authorities did not check, people might criticize them for not doing so.
However I would not expect to get anything useful myself. I don't expect these guys to be local and they probably bought their guns and ammo and practiced with them elsewhere. Otherwise, they are less intelligent than they have been exhibiting to date-- imho.
What I might consider is opening the sweep of local low cost motels (HoJo, Motel 6, etc.) to a large "donut-shaped" area with the shootings roughly in the concentric center. I would start with the large chains and then cover smaller mom-and-pop motels. What I would look for is a credit card number or description of one to three guys, ages approx. 20-32, who moved between hits from one motel to another somewhat further away but still inside the "donut". I would focus on credit card moves over the weekend. If nothing turned up, I would focus inside the donut area, and if nothing turned up still, I might consider somewhat higher-class places such as Mariotts.
If I am right, that check ought to turn up something.