So you are challenging the notion that constrictions raise pressure or that raised pressure can damage guns because there isn't a specific warning about a specific form of constriction published in manuals? There are lots of ill-advised things you can do that aren't mentioned in manuals. A really common one is people "cleaning" lead out of a barrel by shooting jacketed bullets through it. That raises pressure too. Most people get away with doing it, but Allan Jones, who was in a position at CCI to hear about problems from a large customer base says never to do it, as he had seen a number of guns damaged by the practice (bulged barrels and stretched frames, IIRC). Out of ten thousand people following the practice, how many? I have no idea. But I don't see manuals bothering to mention that you shouldn't do this, either, even though they will tell you not to if you call and ask.
What the S&W revolver manual does mention is:
• Cleaning is essential to ensure the proper functioning of your firearm.
and,
• Remove excessive firing residue from the bore and chamber using a properly fitted brass brush dipped in gun cleaning solvent.
It also suggests that any time you notice a case is difficult to extract, you stop using that ammunition immediately and clean the bore and chambers before trying it again. I think these cover the basic situations possible here.
Ruger's manual says:
• Firing a revolver with oil, grease, or any other material even partially obstructing the bore may result in damage to the revolver and serious injury to the shooter and those nearby.
and,
• Improper Lubrication Destroys Guns
If they don't like oil in the way of a bullet, how much less would they want lead in the way of a jacketed bullet in either the chamber or the bore? If that seems too non-specific, call them and ask.
In his book, The Rule of Nobody, Philip K. Howard describes the most recent attempt by Medicare rules to cover every possible medical diagnosis (120,000 of them) included listing diagnoses acceptable for problems resulting from encounters with spacecraft. The gun companies are (thankfully) not massive bureaucracies trying to list every possible hazard contingency. A bit of common sense is required, and avoiding bore and chamber constrictions seems like a good example of that to me. A prudent generalization is to assume practices not OK'd in the manual are not a good idea unless proven otherwise. The reverse, assuming everything not warned against in the manual is automatically OK, is imprudent IMHO. The instructions are not comprehensive. When in doubt, call the maker.