first of all, are you 100% sure its the bbl that is causing the interference and not the receiver? For instance, if you take the bbl out, will the upper & lower Nomad part fit together properly? I ask because I have spent some time dremelling down an area that I thought was the problem, and it was actually hanging up on a different area.
That being said, if it is the barrel ring you can easily dremel this material away. I use a bit that is shaped like a router bit. My dremel is hooked into a sewing machine pedal so I can vary the rpm. The Nomad stock is pretty rigid, but, it is a plastic and if you tear at her at 30,000 rpm, its going to start to melt. What you don;t want to do, is go too far and gouge out where those screw holes are.