Mine was a bear to get off as well. I got a flat back 110 in 7mm off Gunbroker for 200 bucks. The barrel wasn't worth trying to sell so I just clamped it in the pipe side of my bench vise. I couldn't break the nut loose with a 16" pipe wrench and started turning the barrel in the vise when I added a cheater.

I ended up taping up the action and used a grinder with a cutoff wheel and cut between the lug and nut. I only cut about half way through all the way around and then it twisted right off.

Waiting on a barrel, nut and lug from Northland now.