OH, sorry forgot to mention you could also just use a "cylinder choke" tube that is not tapered at all, but just strait inside. However, I would not recomend the choke tub, but I woudl definately recomend getting a dedicated slug barrel.

P.S. You can get a second barrel for an 870 for a fairly reasonable price. If you do, get a slug barrel with a cantilevered scope mount. When you change the barrel, your scope should still be sighted in because it's attached to the barrel instead of the stock.

I use Remington Sluggers in my smoothbore 20ga 1100. I have shot at least half a dozen deer with them, and never missed. Farthest was about 60 yards.

Best bet would be a fully rifled bbl with a cantilever and scope with Sabot slugs.

If $$ is an issue, Remington sluggers are not very expensive--much cheaper than a sabot slug & the sabot won't fly straight out of a smooth barrel anyway. Make sure to use the cylinder choke. If you shoot slugs through a full choke, you're going to have a problem. You can probably get the choke at Walmart if they have it in stock. Check the package yourself--"cylinder" choke for Remington 12 gauge. Some of the Walmart employees don't know their you-know-what from a hole in the ground. (Some do, but don't rely on them--check it yourself).

I also have an 870 with a smooth bore, I called Rem. & they said to use an improved cly choke. for slugs ( I am using reduced recoil sluggers as I have health concerns.)