I have a universal carbine with a front sight that has a set screw. I got a new bayonet lug piece to put on it to replace the one on there now. The piece that slides over the barrel and the forend clips into. My problem is the sight has to come of to replace it, and I can't get it off. I have sprayed pb blaster onthe sight and in the hole where I took the sight screw out, and I just can't seem to get it to loosen up. I don't want to mess the barrel up. Any advice is greatly appreicated.