I have an 870 that came with a barrel marked mod.

All i have done is use a forcing cone reamer in the chamber.

It does shoot tight always has but it seems to put more shot in the head.

I also load my own shells with hard number 5 shot.

I use it for everything quail and other birds and also for skunks ,also have used it ti give warning shots to the neighbors dogs when they are here at the house chasing our critters.