[on2wheels52]

"I'm sorry to say that if you build test barrels that are identical in every respect you will definitely not be able to see the differences between a 10" , 18" or 28" barrel with modern loads. What you gain in longer flight time is less than you gain in greater pellet deformation. Simple ballistic aerodynamics."

I'm having trouble absorbing this. Can we take it to an extreme and make the barrel, I'm thinking about 6" is the shortest one could go and still have a working choke, and not have any trouble at the trap range breaking birds? I'd have to see it done.
I have it that optimum shot velocity comes from a 22" or so barrel, I have no idea what the drop-off would be in a 10" but it would have to be considerable. That loss would have to big impact on terminal ballistics. Unless decreasing pellet deformation is the 'holy grail' of increasing performance. I had thought the plastic shot cup had pretty well taken care of that but perhaps there are gains to be made.
I'll submit I would likely score the lowest on a trap range of any posters on this thread, perhaps have sold more shotguns than most though. Occasionally I use the line "they're all just pieces of pipe" and "I could build a zip-gun that would shoot about as good as anything on the rack".
Jim