Clarifications
I might make the observation that none of the comments of Brister or O'Conner involve taking a barrel that is a 2-3/4" and patterning, and then trying lengthening the chamber on the SAME barrel to test pattern again. The haphazard manner of randomly shooting different barrels, and comparing the aggregate, is not scientific or controlled, just averages.
I refer to SPECIFICS only, in that even though they may not have tried going from short to long, I HAVE gone from long to short.
There is a marked difference, especially when you are trying for the edge of performance, not the spread of a skeet pattern.
The other situation that may be noticed is the random alignment of the chamber to the bore via the forcing cone.
Picture 1 shows the 4 o'clock position of the forcing cone is much more than at 10 o'clock position of this 28 ga. O/U import.
Picture 2 shows more shadow at 5 than at 10 o'clock.
Picture 3 has much more shadow at 2 than at 8 (12 ga. import semi)
Picture 4 has much more at 9 than at 3, and you may notice that there is more total shadow, since the bore diameter of this side by side is much tighter than the bore of picture 3's barrel, and the chamber is also larger in diameter, so more expansion (radially) of the shell, and more squeeze to a SMALLER than normal diameter, adding more injury to the load than normal.
A sample measuring of chamber length of barrels marked as 2-3/4 has several answers for nominally equal barrels:
Winchester 37, 2.6" with forcing cone roughly 1/2" max
Remington model 10, 2.65", forcing cone max. of 3/8"
Winchester 1200, 2.75, with 7/16 forcing cone
Savage single shot, 2.8", .3 forcing cone
Have several NIB 1100 barrels from the Remchoke intro. period that have 3" from the factory, but marked 2-3/4, with the 2 gas ports, too
Have seen factory chambers of varying length, diameter, mating alignment to the forcing cone/bore transition
12 gauge bore diameter variance, not counting backbored barrels sold by the factories, have been from
Ithaca 37 magnum, .715
Browning BPS and many others, .717
Winchesters of 1200/1400 to .736+
Remingtons (1100, 11/48, etc.) from .721 to .746
Total variance for conventional barrels marked 12 ga. and of significant production, in excess of .030 difference, almost enough to make a full choke in a lot of barrels.
So if we look at the random nature of several barrels, with different amounts of off-center nature of the forcing cone, difference of bore diameter, variance in chamber diameter, nominal length chamber differences of barrels marked as being roughly equal chamber length, typical choke action of shotguns being sometimes markedly different for the same choke markings on otherwise identical barrels, patterning differences of shells, weather conditions of temp/humidity/wind variance even across a few hours, and yet somebody will then make a pronouncement from on high, since they happen to be a well-known and respected (even by me!) writer, well, I say the answer is still known by physics, not questionable due to anecdotal shooting reference without scientific controls.
I made tests on one barrel with lengthening the forcing cone very long (much longer than Ralph Walker mentions in his book, I guess you know who he is?) of an 1100 skeet barrel, patterning at 25 yd. with the same box of AA 9's 1-1/8 oz. shooting on paper roughly 40" square, admittedly less than purely scientific analysis.
"Before" tests had 550-580 pellets on the paper, and "after" had 620-640, and there are only about 660 in the whole shell. So, about 10% of the total shot load that had been OFF the paper was now filling out the fringes, for more liklihood of getting a bird being shot at (and less likely to chip a clay or wound a bird not in the aimpoint area), but the center was not any tighter. In fact, the center where formerly doubles and triple pellet strikes in practically the same hole had been present, were now exhibiting some spread between them!
Conclusion to me was that the center became more uniform without being denser, the fringes became more filled toward the edges, the flyers were markedly reduced in number and dispersion, and many of my shooters have remarked how even small gauges with fairly open chokes can reach to much farther distances than they have been capable of, previously.
Their comments are decidedly unscientific, but the body of weight that they represent has me convinced that they aren't lying, just to make ME feel good, so I make this small claim to refer to my experience as significant, if nothing else.
I have personally inspected highly engraved O/U's, high dollar trap guns, combo sets, and have seen ALL of them have crooked choke hole installations FROM THE FACTORY!
Someone owning a Rolls is not necessarily smarter, just richer. Somebody being a champion racer is not the same as being a racing mechanic, maybe just a better example of hand/eye coordination and experience.
No one should necessarily consider themselves the answer to all questions, but may be capable of deductive reasoning with SOME questions.
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