Most of those Spanish guns are copies of the S&W externally, but use Colt-type lockwork, so the normal "rules" for working on S&Ws don't apply. Neither Colt nor S&W parts will work and nor can they be made to work.
Deth_lives, if you want to keep shooting that gun, please use only light .38 Special loads. No +P or +P+ or the hot 125 grain bullet loadings. Some of those guns had the maker's marking and are of reasonable quality. But the majority had no manufacturer's name, and were made from cheap cast iron. I have seen several of them blow up, shattering the cylinder. One broke in half and another blew up when firing blanks.
The asking price on the one on gunbroker is absurd; you can buy an S&W Model 10 police turn-in for that "buy now" price or only a little more.
Jim
