For all of you M-4 gurus I have a problem I can't seem to resolve. On my DPMS suddenly the buffer retainer slips off the spring and down into the trigger assembly. This will not only happen in live fire but also when charging the weapon, not every time but often enough I would not grab this long gun in a problem situation. Any ideas what could be causing this would be appreciated. And yes it is clean and no it is not dry.