Unfortunately it does take some testing to find the best combination.
I built a trap to catch the shot so we could reload it. We were recovering around 92% of the shot. I think tss has gotten a little cheaper since then, but it still allowed us to test without wasting $5-7 every time we pulled the trigger.
I wound up using an Indian Creek .555 in my M2 20g. It's pretty tight - too tight for some people - but it has worked well for me. In reality, I should shoot another load that provides a more even pattern. I just got tired of testing and wasting money on chokes and stuff.
If you do not plan to shoot over 50 yards, just a tad more constriction than "full choke" will get you there, and really, full choke will get you there in most instances, with A LOT of forgiveness and wiggle room for the close shots. I am an Indian Creek "IC" guy all the way, but I do not shoot an expensive Indian Creek choke with my TSS loads. You do not need an expensive choke to choke down TSS like old school turkey loads (lead, Hevishot, etc). I do shoot a choke that "looks" like an IC choke, but that is by happenstance, not by intent.
For example, a 20G Remington full choke is a .590 constriction, which is what most would squirrel hunt with. I shoot TSS through the .575 constriction choke below and it has an evenly distributed pattern in the 0-10" circles, and the 10-20" circle at 40 yards with 1 5/8 ounce of TSS #9s (590 pellets going downrange at 1100 fps).
These choke tubes were called "Blackout" originally, guess BPS has changed the name to "BlackMaxx" as part of the marketing they do to keep things interesting. They usually go on sale after turkey season for $10-15 off.
BlackMaxx Turkey Choke Tubes - 20 Gauge - Remington 20 ga. - .575 constriction - Made by Carlson Choke Tubes