Do they make different barrel nuts?
Yes they make different barrel nuts. One for large shank and one for small shank. I think what olddav is asking about is the part about not having enough adjustment. I got that too but I would have been looking for longer or shorter not larger in your description. A couple of questions for discovery. Are you using a thicker than factory recoil lug? If you screw the nut as far as you can onto each barrel is the distance between the face of the barrel breach to the face of the nut more or less on the new barrel than it is on the old barrel. trying to determine why the barrel nut restricts the headspacing process.