My 870 Wingmaster
will shoot Fed Truball slugs, and Win PDX1 slugs into 3 inch groups at 50 yards, but has a 9 inch vertical dispersion with both brands at 100 yards.
I am shooting a Cylinder choke smooth bore barrel. (Actually no choke at all, to be quite technical).
As for choke, conventional wisdom is that Cyl, Imp Cyl, and/or mod are best for Foster design rifled slugs. Full choke is not only frowned upon, but also may be dangerous in some barrels.
As for which slugs are best for smooth bore barrels, every barrel is different. However, the Foster design slug is best for smooth bores, and sabot design slugs are best for rifled barrels, and rifled choke tubes in smooth bore barrels. As mentioned by other posters, you will just have to shoot several brands of Foster style rifled slugs to see what your 26 inch smooth bore barrel does best with. Same thing with trying to answer the question about what kind of accuracy will you get at 100 yards, i.e., shoot several brands of slugs and see what you get. In other words, no one can tell you what kind of accuracy to expect with what brand of slug at 100 yards, or even at 50 yards.
So, the bad news is that you are going to have to do a lot of shooting. The good news is that Foster style slugs cost only about $1 a shot, vs. Sabot slugs which cost $4 or $5 a shot!
One study I saw published in a magazine indicated that a rifled choke tube needed at least 5 inches of rifling to effectively spin a sabot slug enough to stabilize it. I have never fired such a combo in my 870, so I can't speak from personal experience.
As for which choke tube vendor to use, I would say start with Remington, for your 870. Their IC and Mod choke tubes are on the shelf at any Cabelas, Gander Mountain, Academy, and most LGS's. For a 5 inch rifled choke tube, I can't say. I don't think Rem Chokes are that long.
Remember, if you buy a rifled choke tube, you have to shoot the expensive Sabot style slugs thru it to get the most accuracy potential. And you have to try several brands of Sabot style slugs to determine which is most accurate in YOUR barrel. Nobody can tell you which Sabot slug brand will be most accurate.
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