There's another way to tell the effective choke, not the actual by the numbers choke.
You mention trap. If a solid hit produces smoke a large percentage of the time, you need less choke. If your hits are chippers, you need more.
Smoke indicates excess density, which costs spread. Most folks take their trap singles at 33-36 yards from the muzzle, so gauge accordingly.
Depending on the load, a by the book Mod choke(20POC) can give patterns from Light Mod or even IC to well nigh Full.
Before we all had gizmos to screw in to our muzzles, shotgunners adjusted their patterns by shell choice. Cheap field loads gave open patterns, trap loads were tighter.
Oft I would hunt with my first 870 and Full choke with a cheap load of 8s in the chamber, followed by a long range load of 6s. I might even stick a trap load of 7 1/2s in between. It worked for me.
You should pattern and/or as sbove. Then, if the results are not to your liking, adjust your load or choke. Only one at a time,of course....