Ian Fleming fired a Walther pistol into a fire place in a hotel room. He shot a chunk of wood. Nobody even noticed he had done it.
Legally you should not discharge any firearm, air gun or otherwise, within city limits. Aside from the danger and legal issues, you also have the risk of damage to property. Personally I have fired my airsoft guns numerous times in doors with no adverse effects, legal, property damage or nosy neighbour wise.
Be smart and be safe, but I do not see a problem with what you are doing. If you want a mid velocity, spring powered gun try and get your hands on a G&P shotgun, a local airsoft store may have one for cheap. Single shot, less likely to break easy, cheap and of course kind of cool looking.
Originally Posted by TokyoSeven
1+1 = 2
Were you maybe expecting 1+1 = donut?