I am unsure of the exact terminology, please bear with me. Custom Glock 43 with cerakote finish. Custom match barrel will not work. Second one arrived, didn't work, either, so I asked to take a look. The original stock barrel fits in with fore and aft slop in the ejection port, which allows slide function through tipping of the barrel. The replacement barrel will barely drop into the slide and has no slop fore and aft. This fit appears too tight and prevents the slide from fully moving onto the frame. When I measure the part (sorry, I don't know the term) that fits into the ejection port, it is 3.90 mm long on the original, but 3.92- for the replacement. This is apparently a well-known and respected replacement barrel maker.

Could the cerakote have built up thickness sufficient to prevent function?

Has anyone else experienced this kind of failure of a quality aftermarket barrel to seat itself into the slide?

This issue, especially the measured difference, has me wondering about the advisability of using aftermarket parts, particularly on defensive weapons.

Note this is not my weapon, has just puzzled me, and raised concerns about other modifications my good friends have done or are considering.