If your adapter plate does not slide into the dovetail freely, ensure that both adapter and dovetail are clean and free of debris. If it is still too tight, you may need to touch up the mounting surfaces of the adapter with a very fine file or sandpaper. Go slowly and check fit often, and the result will be a perfect gunsmith quality fit. You can see our handy guide here: ATOM Adapter Fitting Guide. If the adapter seems to be extremely oversized, please contact us so we can take a look and make sure everything is in spec.