Ghurka

I want to use the barrel for a different build so I took off the hand guard and low and behold it's an "Enhanced" upper. The barrel nut looks like a Mil Spec barrel nut that's been screwed into the upper barrel extension. I removed the little set screw that's in the barrel extension just in front of the ejection port and the barrel nut will not move. I applied heat, still no joy. Am I forgetting something?