870 Slug Barrel Accuracy Issues.

[Trkychsr]

I have a 20ga 870 Field combo. The turkey barrel is great, patterns really well with the choke I have. The rifled barrel however is giving me grief. First couple of shots are great but then it all goes to pot, some shots low, some high with no consistency. This will be my second season with it but it's done this from the get go. I got a deer with it the first year at 80yds with the first shot. I've tried several different brands of ammo settling on Winchester Copper impact. Accutips were terrible from the start. I have a Burris 1-8 power scope on it and everything is torqued to spec.I used a 12ga 870 Express for years and that one was accurate out to 200yds.

Any ideas? TC

[Creatineboy]

I have a Remington 887 with rem chokes and there are two kinds of rifle chokes. One for full bore Foster slugs which Mics out at around .725 and there's one for sabbat slugs which Mics out at .715.
What size does your barrel Mic out at?