Cleaning pellets as indoor ammo?

Hi all. This is probably a bad idea, but I can get around 12 yards down a hallway, and into a closet, in my house. I was wondering if it would be possible to use cleaning pellets in a low power Umarex Strike Point pistol for "rainy-day" indoor shooting. The Strike Point is a multi-pump pistol, but is fairly low power with just one pump.

Bad idea? Would this damage the gun?
Thanks all;
Artie
 
I set up an indoor range in my basement. 12 yards on the dot. Built a pellet trap with phone books and cardboard and that electrical putty stuuf (my mind has gone totally blank on what that was called) shot the old 760 pumper at 5 pumps. Then i took the phantom springer down for 1 shot and the wife threw me and the gun out the door. I am now forbidden to shoot in her house. Lol i still set up on my covered porch and shoot into the side yard (20 yards). As long as the wind isn'tblowing too bad I stay dry (of course the targets get soaked)