42 luger

He means the takedown lever. Barrel release is close enough to tell the meaning especially because just above it is a partial serial number on left chamber side of receiver. Me thinks someone ground the s/n off the front of frame below barrel and on left side of receiver. Why? That is puzzling--why would someone grind serial number off a firearm that he had legally and that was not used in a crime? A partial s/n might remain on the barrel and with some clever insights, we might be able to estimate the letter suffix.