Those Carlson chokes appear to be a lot tighter than Briley.That's odd. Carlsons chokes for 20ga inv plus are .015 (.615) for LM and .020 (.610) for Mod This is based on a .630 bore diameter.
Carlson 20ga. Inv plus
I love light mod for my monte 20. On benelli sight they have light mod sporting choke for $55 which briley makes for them and comes out of Missouri from MWG works(non ported).I am considering a Briley choke tube for my Montefeltro 20 gauge. Thinking either light modified or modified. What do you all think and do you have any experience with this extended ported tubes?