Kai - If you are able to tighten it down and the only problem you are facing is wobble, is it barrel wobble or the RIS shaking forwards and backwards making that annoying click noise? If that's the case, just add some electric tape to the front and back of your RIS, where it meets the rings so it won't be seen. It'll give you a more solid fit, and won't clack around anymore
That being said, now most of your front end is being held together by the friction of electric tape. That might be something to worry about.