No experience with Rio steel, but shot a lot of their lead "Mini Magnum" in Remington 870 and 11-87.
The Remington full choke tube did not shoot well with #2 shot or buckshot, of any brand. The patterns were blown with very few pellets in the centre. Modified choke was much better.
It would be worth shooting a few patterns on big sheets of paper/cardboard and see what's going on. Those Remington chokes are quite short and the bigger shot sizes seem to have trouble.
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