Re: issue with S&W .375 mag #686
It's one of two issues, neither is serious and both are easily remedied.
A) - There is a carbon ring of burned residue inside the chambers from the shorter cased .38-Specials. If the ring is there, longer .357 cases won't easily drop in. Take a fired .357 Magnum case and run it all the way into each chamber. This scrapes out the majority of each carbon ring, sometimes enough for you to begin shooting .357s without sticking. Better yet, scrape the chamber walls as described and follow with a good soaking of powder solvent and then use a .40-cal wire brush dipped in solvent.
B) - Some really out of spec ammo where the bullets are seated so long that the bullet ogive hits the forcing cone in every chamber. Try different ammo.
Either way, it's not the gun and don't worry about a catostrophic failure!