I am building a drop in barrel for my Thompson Center Seneca and I need the wedge-pin underlug. Track of the Wolf told me they had one but they don't. Thompson no longer has these underlugs for that gun. Track has some "staples" they use but they look rather light duty compared to the factory underlug. Does anyone know where this underlug might be found? Has anyone used the staples and what have been your experiences? Do they stand up? Thanks. Hank