Interpretations of .410 full choke constriction seem to vary widely. Winchester had .017 in my M42s. My Ithaca ICD has .020. My Ugartechea had .025. A friend's 2 Perazzi guns had .036-.037.

I have a gun a previous owner opened the chokes to .000 and .010. I shot a lot of birds out pretty far with that cylinder bore. I believe the fact that I have very long forcing cones in that gun contributes greatly to the tight patterns.