The severity of the forcing cone angle and the cones surface condition are primary reasons why wad petals are sheared off. Note: It takes a bit more than a sandpaper polishing to do that right.
Neo is spot on correct about that.
Doing it right is the trick.
ALL my s.g. barrels get polished. I mean polished to a mirror shine.
I use 4000 or 600 grit past to start out and rotate the tight fitting rag on a dowel chucked in a 3/8" drill and keep the speed constant and the in and out motion constant.
I finish with 1200 grit.
Paste is non imbedding from Brownells and it takes some time to get in right.
Rifled barrels don't get the drill treatment, it's all elbow grease and lots of it.
Leading and plastic fouling almost completely disappear.
The aboslutely roughest barrels i've seen are Mossy's and they realy benefit from a serious polishing, nest in line are Rem 870 barrels, some of which have deep machine marks inside of them.
It definately aids accuracy like you won't believe.
If I get BVR retraining as an injured (crippled) dispalced (GM) worker as a Smith I'll specialize in forcing cone work and barrel polishing as well as metal treatments. When I'm done nothing will rust or corrode accuracy improves and fouling is minmized.