I have a remington 870 and think it has a modified choke tube in it now. My problem is I can't seem to get any kind of a pattern when shooting XXX buck shot. I have tried all brands of shells which leads me to think it may be the choke. At 50 yards I may get 1 of the 8 pellets in a 10" pie plate.
Any suggestion would be helpful.
Thanks Dale

You're probably experiencing severe pellet deformation using that load and choke combination. I'd use a "cylinder" tube. It's basically no choke at all. Like open cylinder.

I have an old 870 Wingmaster with an Improved Cylinder choke that shoots 00 buckshot and rifled slugs pretty well. It's my first and only shotgun, but I'm satisfied with the patterns I get.