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.