[TC Rider]

You probably still have a slight ring of lead and/or assorted fouling in the chambers that are preventing the .357's from seating. Used to happen to me a lot with certain revolvers and types of ammunition.

There's your answer.

The cylinder is cut for the longer .357s. Shooting the .38 will foul the clyinder between the end of the 38 case and the cut for the headspace for .357s.

Wet some patchs in bore cleaner, swab your cylinder and let it soak for 15 or 20 minutes, scrub briskly with an oversize bore brush if you have one. Like .40/10mm, or even a .45 brush.

Repeat as needed.

[ladyrustic]

Thank you for your advice, I'm going to follow it exactly.

From what everyone's saying it sounds like that will solve the problem quickly and inexpensively (no gunsmith required in all probability)