Comp N Choke .390 in SumToy thread. Shipped for $55.00 just paid $75 for it.
So I had a Mossberg 510 18.5" barrel threaded by William and tried his chokes .385 and .375. With the best results with the .375...
So just to make sure I wasn't blowing the pattern I ordered a more open choke like this .390. With one shot I could tell I needed tighter. The .370 works better for me.
If you have a longer barrel with his threads this might work well for you.
Thanks for looking.
God bless.