I have a theory on chokes, the smaller the bore, the tighter the choke you want. Here is why I say that. As SH suggested, the bore size has zero affect on the size of the pattern. How do I know this???, because, being a muzzleloader guy, I have played around with ML shotguns from 8GA to 20GA. Being ML'ers, they are all cylinder bored. At a given distance, they ALL throw the same size pattern. Naturally, the bigger the bore, the more shot and therefore the denser the pattern at any given distance. When you reduce the size of the bore, you need to increase the choke to maintain the same pattern density by reducing the size of that pattern. Look at it this way, shoot a pattern from a big bore shotgun with an open choke that is throwing a 30" pattern at a given distance. A small bore with a similar choke will also throw a 30" pattern at that distance but obviously with a much more open pattern (far fewer pellets). If you choke that smaller bore down to reduce the overall size of the pattern, you can effectively get a similar pattern density but in a smaller circle. A full choked .410 will throw a pattern of similar DENSITY as my cylinder bored 8GA, just a MUCH smaller circle. Bottom line, they will both kill (be it live birds or clays) equally if said target is in the middle of the pattern. The bigger bores just provide a bigger "fudge factor". If you are a GOOD shotgunner that can centre your targets consistently, you will get just as many kills with a 1/2OZ from a tightly choked .410 as you will with 2OZ from an open choked 10GA. OTOH, if you shoot shotgun like I do and you want to compete with GOOD shooters, you might want to try a cylinder bored punt gun throwing 4-5 OZ of shot if you can swing it (literally and figuratively).
