Any one shooting a 26" 870 20ga ???

[owlhoot]

Oh, are you sure your shooting at 40? Long 40 paces could have put you at 45-50. 10 inch circle ?
hated to ask that. But you sure shot alot of chokes and loads to get 120.
Maybe alcohol clean the barrel like Sumtoy has said?

[Punisher]

I average around 150/10" with the Sumtoy 562-5.  I have tried a few different chokes through my Rem. 870 26" gun and this choke gave me the most consistent and even patterns.  Might be worth trying.