I'll also pass this info along about 2 brands of choke tubes to use that will simply put save you a lot of money of buying the more expensive choke tubes that are out there. H.S.(Hunters Specialties) Undertaker choke tubes are simply one of the best choke tubes I have yet to try.
http://www.hunterspec.com/Updateable...&categoryID=33 You can get them at Wally World for $20 not counting tax. They will give you about 90% patterns at 40yds using 5 or 6 shot in most guns. I use this choke tube(.695 constriction) as I stated earlier on my Mossberg 835 barrel. It is one of my favorite choke tubes. The other brand is Carlson's choke tubes. They make some very good ones as well.
http://www.choketube.com/
Don't be misled by choke tubes offering slots that supposedly stop the wad for denser patterns. That is simply put not true. I will say that the Comp-n-Choke brand slotted choke tube does shoot very well. But again the Undertaker choke shoots just as good and maybe better. The thing I have also learned that even the exact same brand choke tube say if you buy 3 of each is that one will shoot just a little better than the others. I have seen this to be true through my testing. A good choke tube constriction for most barrels on the market for 12GA shotguns shooting heavy #5 or #6 turkey loads is .665 constriction from my findings or say .005 up or down from it. For #4's in most shotguns I would say .680 to .690 would be the best. On Mossberg 835 barrels, .675 to .680 is about perfect for #5's and #6's, and .695 to .705 seems to be about right.
Also I can share with you guys that you can play with choke tubes such has I have and experiment with buying say .005 tighter or bigger or .010 tighter or bigger size chokes, but .010 to .015 choke constriction in these turkey chokes isn't going to be much of a difference that you will even notice. That has been my findings. Save your money and stick with some of the choke tube brands I mentioned and those particular constrictions.
Hope that helps some who would like to know.