I have the same gun. It shoots a .38 S&W. Though it is a .38, it is much shorter than any modern .38. That's why your round will only go in half way.
.38 S&W's are hard to find, but, they are out there. I bought a box at my local gun dealer. It was the only one he had. He said, "thanks, I thought I'd never get rid of those damned things.