So I put together a new lower and the three ProMags that I had would recatch after release about half way out! Pmags worked perfectly fine! Also the ProMags worked fine in my other AR15 so I was almost ready to just set them aside! Then realized that they were catching agian on the 556/223 stamp at the top of the mag! So I went over it with a fine file and they work perfect! Just a FYI!