I have actually had good luck with this dot sight. Not a scope, but handles my air rifle I have it on which has killed more than a few good scopes and sights that cost $50+. This one was $19 and paired with my air rifle they shoot 1/3 inch groups at 25 yards and a 2 inch group at 90. My gun is a gas piston and the nice thing is it is pretty cheap so if it doesn't work on the gun it isn't a loss. Plus it has an aluminum shell and actual MOA adjustments unlike many other cheap dot sights.
Amazon.com : MASSWELL (TM) 1X 40 Red/Green Dot Sight Scope Tactical Weaver Picatinny Mount Five Brightness Settings Illuminated red Reticle : Sports & Outdoors
Amazon.com : MASSWELL (TM) 1X 40 Red/Green Dot Sight Scope Tactical Weaver Picatinny Mount Five Brightness Settings Illuminated red Reticle : Sports & Outdoors