Does the Rem Chock mean that they have interchangable tubes?
Yep, but you got to buy em for the 870 express. Comes with a modified. You get 3 extra with 1187 and wingmaster.
I get 2MOA accuracy with 2.75" copper solids and 2.75" federal hydroshoks. I get 3MOA with winchester partitions. You got to experiment. Most slug guns don't like 3" or the ligher, faster slugs. You get some good groups but then unexplained flyers. It gets 3MOA consistently with lightfields. Same with my browning gold with cantilever barrel.