[ILLusion]

There's another explanation to the problem, but I didn't mention it earlier as it's rare:

Over time, improperly matched metal barrels to slides will cause damage to the upper rear portions of the ejection port of the slide. It's caused by the slide bashing against the top of the chamber as the slide cycles forward. I've seen in rare instances where the slide has bashed the chamber to the point where a "lip" forms from material being pushed backward and riding down in to the path of the loading nozzle. The result is the loading nozzle raking against this lip and a point of friction is created. This can be easily recognized by heavy scratching on the top of the loading nozzle.