The only reservation I would have is the use of 9mm bullets, which are 0.355" diameter. Allegedly, the .38 S&W groove diameter is 0.360, so the smaller bullets might not be engraved by the rifling very much. But 0.357-0.358 bullets have always worked OK for me.

I have pulled some lead bullets from antique .38 S&W loaded cartridges for measurement, and have found they run 0.357-0.358.

For even cheaper shooting, use 0.375 lead round balls (as used in .3 C&B revolvers, or much cheaper still, use wax (parrifin) bullets with primers only - but drill the flash holes larger.