I don't know how water in a barrel could do that much I know in 1974 that piece of crap M16 still shot full of water but it would not shoot with any thing else in it like powder carbon or bullets if you didn't stop and clean it every 10 minutes Hell it probably had 10 carbon rings one for every other shot.
Which brings us back to the Gun Slicker, which I learned about in this thread. I ordered 3 (@ only $24.95 each) from Alpine Innovations (the mfr) and received them in 3 days. They really do fit well and are super easy to apply. They also roll up into a small carrying pouch. Check out their website.I agree and don't believe water alone was the cause either. Elkaholic has confirmed that to his own satisfaction, and it didn't take any effort to convince me. Rich did confirm carbon fouling. So that's the primary suspect. Or more specifically, wetted carbon fouling.
Difficult to recreate the same carbon conditions in his throat. And who wants to soak their barrel in water over and over again in the effort to confirm the affect of wet carbon. I prefer to keep my rifles dry, rather than repetitively soaking them for test purposes. Thus prevention is the simplest path of least resistance going forward.
PB B really works well on carbon. I use a piece of tubing in the chamber and squirt it in with the muzzle down. Let set for 5-10 minutes.
Do you use a bore brush or just a patch with the PB after it sets for 5-10 minutes? Does the PB remove any copper? What solvent do you use after the PB to finish up with? I have been doing the Bore Tech Eliminator for my cleaning chores, but not sure if it has any effect on a carbon ring.