I'm not sure exactly what your talking about? , what lug is it and what purpose does it serve?
I haven't ever done anything more than just clean and sight in any of the Rem pump and auto rifles so thats why I'm not sure what it is yur looking at. I know that part of being a gunsmith and machinest is having to make your own tools so maybe one of the smiths here have one or have an idea what to get to make it work.
i was refering to the barrel extension which has the internal locking lugs for the bolt head to turn & lock into when the action is closed. this is threaded onto the barrel threads behind the barrel lug.