Which Shotgun Bore Diameter Gives The Best Pattern?
I am often asked the above question by people who are interested in purchasing a new shotgun. They reason that if a specific bore size inherently gives better, that is more even patterns, then it makes sense to purchase a shotgun with that bore diameter.
Shotguns that were made in the U.S.A. were for many years all of the same nominal bore diameter of .730 (plus or minus the tolerance of the individual manufacturer) as the U.S. standard for 12 ga was .7299. With the rise in popularity of foreign shotguns such as Beretta we were introduced to smaller bores running in the nominal .721/.725 diameter. Stan Baker to the best of my knowledge was the first to do extensive experiments with backbored barrels (the process of enlarging an existing bore diameter) taking the 12 ga bore up to a nominal 10 ga diameter of .775. Some time back Browning added a new choke design to their line which they named Invector Plus to differentiate it from their original design called Invector. The new chokes and the barrels were based on a nominal .740 bore diameter. I believe that Browning was the first company to offer a factory barrel with a bore diameter that was significantly larger than standard. Currently most of the major shotgun manufacturers offer at least some models with bores larger than their “standard” bores. Some have gone totally to a new larger bore. The results of this are that today’s shooter has a very wide range of bore diameters to choose from.
Pulling from my memory I can recall the following nominal 12 ga. bore sizes. These may not be exact numbers as each manufacturer has plus and minus tolerances. Some of the below numbers have been rounded when converting from metric measurements and some for my convenience.
Now that you have all of the background information, you can get my answer.
I have always been able to obtain the pattern that I was looking for within reason (no 100% patterns at 80 yards) with all of the above bores by patterning with different chokes and or shells. I have had shotguns on occasion that took quite a bit of work to obtain the pattern I wanted but this has never been limited to a certain bore size as they have always been a random mix.