I got 3 gen 1 poly 80 Glock 17’s. Built all 3 and took to the range. 2 worked fine no issues, the third fired full auto. I took them home and disassembled them and replaced the parts from the full auto with the parts from one of the ones that worked properly. Went back to the range and still fired full auto. After disassembling again I noticed I had filed the rear slide rails very thin. This was the only noticeable difference in lowers. Could this have caused my problem? Any input would be appropriated.
The short answer is 'yes'. If the cut between the frame and the bottom of the rail (red arrows in the picture below) is too wide, the rear of the slide may 'lift' as it slams into battery and pull the firing pin lug off of the cruciform sear, thus releasing the firing pin. The longer answer is that there are several attributes of the Glock design that affect just how much the firing pin lug overlaps the cruciform sear. Fundamentally, anything that could change the relative positions of the lug and sear is suspect and includes the ... slide slide channel liner firing pin firing pin lug trigger bar cruciform sear tab trigger bar cruciform drop safety tab trigger mechanism housing drop safety slot trigger mechanism housing fit in the frame frame rails ... and probably some other 'things' that don't immediately come to mind. Furthermore, a 'worst case tolerance stack', that is, a 'bad combination' of parts, starting with suspect frame, is also possible. People seem to believe that Glocks are simple, but they're really not... many parts in the Glock design 'interplay' with other parts... and changing just one part often affects the operation of other parts as well... unfortunately, sometimes 'stuff' happens. Good luck! Best regards, Bob
To help with this issue I measured some P80 rails this eve. Rear stainless rail is about .052" in thickness. Locking block rail about .056" in thickness. Measured multiple guns by the way. Deburred with chamfered edges too. These have all seen several grits of paper up to 1500 grit. All also fire range ammo well, 115g. @Aron Tunstall hope this helps in some way.
