I am working on fitting a JEM carbon steel slide to a 100% JEM stainless steel frame and it’s going well. The slide will go onto the frame by hand with very little force, but it will not slide freely when the frame is tipped front to back.
Some builders shoot for a .0002" side-to-side fit - I’m not sure I can even reliably measure that small!
But I’m thinking about stopping with the fitting at this point and building the gun out for test firing. If the slide ‘wears in’ during testing, I’m good to go. If it does not, I can stone a tiny bit more off the frame rails and the bottom of the slide (the places that there is the slightest contact now).
How bad an idea is that?