I use the oak wooden blocks drilled and split and fit in a homemade barrel vise. Try some rosin in the blocks and a deadblow hammer or a mallet on the barrel nut wrench, but the biggest help I have found is a paint stripper heat gun. You can control how much heat you are putting in a pretty small place. Just heat the nut, slip on the wrench and whack with the mallet. It doesn't take as much heat as you would think to make a difference.