Having a 1 bedroom apt here in crappy Phoenix, I test my stuff indoors using a cardboard box with a bath towel to stop the bb's. -They fall harmlessly into the box.
Once in awhile, I need to use my old "Chrony" crono. For that, I just go out on the teeny porch in the sun and shoot the box/towel setup.
I have been known in the past to go to Shooter's World (Indoor real steel gun range). There's Olympian-in-training air rifle and pistol folks there all the time shooting their .177s, so no hassles. I used the long-rifle bays, where the hunters sight-in, and all's fine.
Chip