We had a lot of trouble getting Briley and Kolar skeet tubes to throw good patterns. Turns out they both have trouble with good forceing cone polish. Putting the 410 tubes in a lathe and polishing the forceing cones with 600, 1200, 2000 grit and then buffing with crome rouge. With .003 chokes my 410 added 24 bb's to a 30 inch circle at 20 yards. Similar improvements were found on 28 and 20. The SS or ti chambers are very hard to polish.
You may want to check your forceing cones.

bill