I am currently shooting a .710 Indian creek in my bps10 with a 24" barrel. Shoots good with both
winchester an remington lead loads. Not too tight, not too open, nice and even, which is what i wanted
with this gun, since i am using only front bead sight. Winchesters shot markedly better than the remingtons, but remingtons were 4's, and the winchesters were 5's though. Both loads would do the job at 40 yards fine. Lot of good chokes out there, you will just have to decide the range you want to shoot, and what load your going to use. Sumtoy could probably make you a custom choke tailored to what you want, but I am unsure if gun parts like chokes can be imported into Canada.