I had this problem recently and called Thompson Center for advice on how to open and remove the barrel....They told me to get a rubber mallet and strike the finger guard sharply, much more pressure than I could apply by hand, and it opened for removal.....The problem was that I had a solid lug instead of a split lug on the barrel.....TC sent me a split lug at no charge to replace the solid lug........If I were you I would call TC and speak to them directly.