I bought a 12ga slug barrel for my encore and couldn't get it to group worth a darn. Went through over $100 worth of slugs trying to find which one it liked. I was ready to toss it but then I started working on it and now it shoots great! Three shot groups under 2" at 100 yards. Here is what I did:

1) Installed the over-sized hinge pin. This helped tighten it up for all of my barrels.
2) Installed the stronger lock spring. Also helped all barrels.
3) If you are going to use a scope, you have to buy T/C's scope base for the slug barrels. It's longer with 6 screws holding it in place. I think it is like $36 bucks but well worth it. I was using the Maxima base but I think it was moving under recoil.

The first two mods only cost about $10 total. Now my gun will shoot sub 2" groups with Winchester Supreme PG slugs all day long. I try not to do that due to cost though. I sold my other 2 slug guns and am very happy with this barrel. I also mounted a Bushnell Dusk To Dawn 3x9x40 on it that has the extended eye relief. Nice scope and I don't worry about the recoil with the supreme slugs.