Alpha-- I shot a very similar set up for a few years a long time ago (870 with a rifled choke). I assume you are putting the rifled choke in the factory barrel with just the bead sight? If so, I tested that set-up at the range quite a bit with Winchester sabots...with just the bead site, you better not shoot beyond 30 -40 yards without a LOT of practice. I later bought a replacement deer barrel with rifle sights and then I got pie-plate size groups at 100 yards easily. A fully rifled barrel will give you lots more range...it basically turns your 1187 into a 50 cal rifle with a good sabot round. And it is a DEVASTATING weapon for deer. If you hit anywere in the vitals, you wont have to track the animal more than 18 inches.

Good luck.