Shooting .38 Special ammunition in .357 Magnum, will in time cause a build-up of carbon and gunk in the chambers,to the point even .38 Special cartridges won't chamber properly.
While true, "over time" means round count, and the number of rounds needed for the dreaded "carbon ring" to be come an issue varies with the ammo used, AND this also assumes one does not clean their gun.
lately, I've been beginning to wonder if this is really the problem so many mention. Everyone agrees it can happen, and can be an issue when it does, but no one seems to give their personal experience of having it happen. There's no one saying "I shot 127 rnds of 38 and then couldn't chamber a .357..." if they are saying that, I'm not seeing it here on this forum...
I can't give you any numbers about it, either, but that's because in over half a century of recreational handgun shooting, I've never had it happen, to me.
Maybe I don't shoot enough, or maybe I don't shoot dirty enough ammo, or maybe I clean my guns well before build up becomes an issue. I don't know, only that I've never had the problem. I KNOW it is possible, but if it is a big concern where are all the "it happened to me" posts???