Screw-in chokes are designed for plastic wads, if those chokes have normal cones and end-chokes. Before the advent of screw-in chokes, chokes had somewhat more constriction
seems to me, with .040" being standard for full choke in 12 & 10 bore, thus a 12 bore full had a .690" muzzle, .040" tighter than .730", it's nominal size. I think the choke constriction
for smaller gauges was less. I do think IMP CYL was .005" for all gauges, though.
Have you tried patterning with just the Imp. Cyl, choke?
In 20 bore flinter, mine shoots tight enough for turkeys to 30yds. and likely 40yards, using a mere 1 1/8oz. shot. More shot could be used.