The upper rails on the NDS M92 receiver I have fit the carrier very tight, measuring from .953 to .973 free space between the rails. The carrier measures .973, so I am not surprised to find it binding a bit. On my factory (Arsenal) guns I find the free space tends to run about .980. Before I take the file/dremel/grinder to the rails, what do you look for as a tolerence between the rails and the carrier? I see the thickness of the rails is different on each side, and it looks like my extra width is on the right rail (looking from stock to muzzle) at this time.