[FlyFish]

You can certainly shoot enough .38s in a .357 to build up a crud ring, but it does take a while and you need to be pretty casual about cleaning. I've never had the problem because I've always been a reloader and it's a simple matter to make up .38 Special-equivalent loads in .357 cases, but I know plenty of shooters who shot .38s and eventually got the ring, which can be a pain to remove but will eventually come out.

One trick I've heard of but have never had to use is to flare the mouth of a .357 case so it just barely chambers and force it fully into the chamber to scrape out the crud. Otherwise, it's brushes, solvent, and elbow grease.