Roger is experiencing exactly that with his 60,000+++ round .45 barrel - and has been, now and then since I joined this forum, years ago - around 45,000 rounds at that time, if I remember correctly (IIRC).
The condition is valid, I'm sure. If you want to maintain that original powder charge, the cure is valid as well - you 'roughen' the barrel or use more powder - either - or. Running a heavy emery, say 120 grit down and up the bore a few times will do a better and more consistant job than the urine soak, I'm sure. The emery is what I'd do, but - I like the added powder myself - accuracy is incredible with it and so is the 'new' trajectory. It's a great thing to not have to think about raising the front sight in the notch for the 100yard gongs, as the ball drops only about 2" at that range from the 60 yard zero. I like that, but in my .40 and .45, it takes 65 and 75gr. 3F to do it - along with the LHV or the stuff I'm using now, Shenedoah lube. 2,200fps+ has a wondeful effect to trajectory of a round ball, compared to 1,500fps.
Running the emery down and up the bore, has it running with the rifling. Peeing into the bore will cause roughness, which is the desired outcome in a random manner - THAT I don't want. That roughenss is pits, however small, it's still pits and they are random, all over.
I want the 'gripping' or resisting to the patched ball for even powder burning thus improved internal ballistics to come from the sides of the lands and bottom of the grooves. I want the tops of the lands remain polished - or with longitudinal marks (from the emery) only. I don't want pits, but maybe that's just me.