I agree completely with most of your comments about aftermarket barrel mods like porting and backboring because after years of patterning many different guns with varying bore dimensions i’ve come to the conclusion that pattern density has little to do with whether or not you have a .720 bore or a .745 bore.
The most important factor besides developing the right load for the right gun in my experience has been to match the correct amount of constriction to the particular bore diameter(for maximum full choke performance).
Example: many european guns have tight bores such as the berettas, belgian brownings, etc. with diameters around .723-.725 and with the standard .035-.040 constriction full choke your exit diameter will be .690 or smaller.
My point is that i’ve found it’s very easy to overchoke these guns with tight bores and more often than not an IM constriction of .025-.030 which keeps the exit diameter around .695-.700 produces superior percentages in many cases especially with screw in chokes which usually have a shorter effective forcing cone than a well done integral choke.
Have you experienced this in your guns or experimented in this direction?
Isn’t it funny how similar experiments by different people can come up with different answers. I have generally found that my pattern percentages increase until I get up to around .040″ constriction. In my conversations with Briley concerning screw chokes, their rule of thumb is that you can generally expect improvement in all guns up to .035″ and many guns will show improvement up to .040″. After that it gets really dicey and depends on the gun. I have shot one Perazzi which performed beautifully with .047″ solid choke.
I did some tests with my Beretta 303 screw choke barrel and found that I had trouble touching 70% with Remington STS shells using a measured .035″ tube. I was able to average over 75% by going to a .040″ tube, but nothing that I could do would get it over that consistently. It might just be my particular gun or maybe it didn’t like that shell.
I have always had trouble getting the tightest possible patterns with factory choke tubes because they usually have such a deep relief at the skirt. That is never good. Perhaps a different barrel, different choke tube or different shell would up my number. I am sure that custom fit choke tubes for my 303 with minimal flare at skirt would improve my percentages, but 75% is fine for my purposes. Generally, I have had better luck getting the highest pattern densities from my solid choke guns, rather than my screw choke ones. I find that my patterns often max out in solid choke right around .040″, not less and patterns of 80% and over are not hard to get. That said, each gun is a law unto itself. Also, the larger the shot, the less choke it needs.
By the way, most of my guns have long cones, the one barrel modification I do believe in.
Shotgun Report’s Technoid
(Often in error, never in doubt.)