Do a search on this site on smooth barrel nut. I just did one on a Mod 11 trophy hunter. The smooth nut proved very obstianate to remove. I used a 15" pipe wrench with my considerable mass on the end before it broke free. Note that I weigh north of 200 so you can guess the torque. My own experience with the Wheeler smooth nut wrench is terrible. I have seen my local gunsmith have the same struggle. I had the replacement barrel grooved barrel nut in hand beforehand. Also I gave the nut a soaking for 3 days in Kroil but any penetrating oil is good. You are correct about the headspace gauges. Another place to check is Midway USA or Gunshack for your stuff.