O'Connersun,
Found it.
The article ran in Vol. 12, Issue 4--Winter 2001 of The Double Gun Journal
title: "Finding Out For Myself, Part V: Long Shells in Short chambers" by Sherman Bell
It's a long article but I think this is a fair summary:
He measured pressures in a set of test chambers/barrels with different sizes of chamber and lengths of forcing cones, and concluded that using standard SAAMI factory ammo from 2 1/2 " to even 3" in a gun machined with chambers and cones designed for 2 1/2" ammunition would not cause failure or damage in an otherwise sound weapon. The small measured pressure increases, he concluded, were nothing to worry about--beyond the fraying of the crimped portion of the hull.
In my experience, no manufacturer agrees with this conclusion
(I've also read articles by gunsmiths about the damage caused to older guns by using plastic hulled shells in guns designed for paper hulls, because the forcing cones were not cut to accommodate the thicker hull material).
The question that started this thread asked about using shotshells shorter than the markings on the barrel--I remembered this article and thought I'd ask if anyone had experience with the consequences of using longer shells than those marked on the barrel.
Thanks for posting your experience.
I'd love to know if anyone else saw the article--and what they thought about it, or this matter of using longer shells than recommended.
Me--I'm with you, about not violating manufacturer's recommendations, and jumping off bridges.