In response to Little Creek's original post I did do research in to the effects of choke restriction vs shot dispersal @ 15 yrs ago. I received from Italy a number of 10ga O/U's, in the white, with fixed chokes F&F of .042" restriction. Utilizing 3&1/2"Remington shells in #2 steel shot I proceeded to pattern at 40yds from Muzzle. Initial results gave a pattern of 68%,it was noted that the pattern was somewhat patchy. I then proceeded to open the lower barrel in .003" increments noting the gradual increase in density. End result was that opening,balancing and final polishing to a restriction of .018" gave an 84% pattern. The intermediate results were progressive and clearly indicated a steady trend.
With regard to "balancing" I usually cut chokes on Mr Greener's principal of equal length cone and parallel section, this however was based on lead shot with e density of 11.xx. For steel shot with a density of 7.3 I increased the ratio to make the parallel section @ 50% longer ie 1:1.5
Summary.
Both 10 & 12ga guns choked as above .018" & .008" will throw patterns of Xfull and Mod performance. I did a number of guns like this and the owners (myself included)have been well satisfied
