the Vortex brand Sparc optic is what i went for when looking for a "cheap" red dot. it had good reviews on ar-15.com and some "torture" tests as well. guy froze it, threw it off and onto his roof, etc. i use it on a .22 but was reading tons of guys on there who used them on their ar's. costs around 200 and i am pleased with it. the reticle will tend to change shape a little with every shot but never gets distorted to the point that it no longer looks like a dot. good luck but i think it will be gross on a shotgun!