It would be interesting to see if any specific brand is better regulated than the others.
This is basis general experiment only, no tweaking or fine tuning was done to seek further validation....
I found negligible difference among the
sxs that I've shot here in Canada.....all shot to POA with reasonably even patterns at 30yds (my shooting distance, normally) into a 30inch circle.
Ammo brands used were mostly Kent and Kent Gamebore 12, 16 and 20. Winchesters and Challengers 28ga. All bird shot, shotshells #6, 7 1/2 and 8......those are almost exclusively what I use for hunting.
The following shotguns were used....choked IC/M, basically default for my guns whether fixed or screw-in.
CZ Bobwhites -12, 16, 20 and 28ga
Beretta 626E and 626 Onyx - 12ga
SKB 200E and 280E - 12ga
Liegeoise D'Armes (Belgian) - 12ga
AYA #3 and #4 - 12ga
Baikal IZH-43E - 12, 20ga
SPR220 - 12ga
LC Smith (Marlin) - 20ga
Ugartechea - 12ga (the only one choked F/M)
As an afterthought, I have a SPR220 hammerless coachgun with 20in bbls and Cyl bores.....plan to test that with Challenger and Brenneke slugs. Will provide feedback as soon as I'm able to.