Got a basement/crawlspace .. something that'll give you 20-30 feet?
That's what i did in my youth.. 30+ years ago now. Break-action single shot .22 pellet gun, using layered styrofoam insulation as a back-stop.. those pellets are still embedded within that wall to this day. The neighbors had no reason to complain about that..
Airsoft isn't all that accurate enough to be used for marksmanship... not without huge $$ being spent anyway.. and it'll always be inferior to a reasonable priced, rifled-barrel pellet airgun.