There's a chance of chipping the extractor. I don't remember anything official one way or the other, there's nothing in the manual or armorer's manual and I don't remember it coming up in the class.Anyone know what Glock says about it?
This is an issue where it's ok with some guns and not with others. If it's not in the manual (either specifically allowed or prohibited) then you gotta contact the manufacturer for the truth.
Ruger P89 & P95 and Beretta 92FS & PX4 are a few that I know specifically allow it in the manual, most just don't say anything one way or the other.