Bike Forums - Drive train fiasco

So right now I'm riding a singlespeed mtn bike with american BB and bmx type drive train. My problem is that the screw that holds the front sprocket onto the crank arm moves has a little bit of play so that makes the sprocket kind of like a oval in the way it turns so one part of the chain is loose and the other part is tight. I have already tried wrenching the screw in as tight as I can and using some locktite on it but it still moves a bit when I pedal hard. I was thinking about getting a new sprocket and trying that. Currently I am using a Shadow one.