An annoying ring of carbon will build up ahead of the brass in the chamber if you shoot a lot of .38 Special in your .357 Mag Winchester or your .357 Mag revolvers. (We do, shooting 120 .38 rounds in the Winchester between us at Cowboy Action competitions and my .357 Ruger New Vaqueros build up a ring, too.)
Eventually you'll feel the rings as you load the revolver and you know it's building up in the rifle even if you don't feel it much. You'll really feel it attempting to load a true .357 round in the chamber and the carbon rings are still there. You'll need to force the round in.
To remove the ring, the best tool I've found is the SliXprings - SliX-Scraper sold by Long Hunter at https://www.longhunt.com/storelh/ind...product_id=320
This tool is a precision scraper with the dimensions of a full-length round -- .357 Mag, .44 Mag or .45 Colt. A blade is machined into it that cleanly removes the carbon ring without harming the walls of the chamber on both revolvers and rifles.
For revolvers, simply spray some solvent into each chamber and drop the scraper into the cylinder like it's a round. Turn the scraper counterclockwise with a slot screwdriver. You can feel it removing the carbon. Then finish cleaning as normal.
For the Winchester, feed a cleaning rod into the muzzle and screw the scraper onto the rod. Pull the scraper into the chamber and rotate clockwise as it scrapes. Push the rod back out of the chamber and unscrew the scraper. Done.
Models are available in .38/.357, .44 and .45 -- the major calibers that have longer and shorter versions of brass, if you're shooting .44 Special in .44 Mag and .45 Schofield in .45 Colt.
You can buy this tool and be done in seconds or brush till the cows come home.