johnch,
i too have the undertaker and am absolutely love it. my 870 with winchester 2oz #6's throws a fantastic pattern. i thru a few remington hevi #6's with awesome results also. i have gone back and forth with an individual from hs strut that says DO NOT shoot hevi thru their standard tube. the final word sounded like you MAY cause tube and barrel damage. i dont have a problem buying another tube(or 4 for that matter....lol) but am reluctant to if they are just trying sell another tube and that i might get a worse pattern