I assembled a frankengun for a friend , and it's showing me a new trick . Upon firing , it will eject and feed , but will not cock the hammer . I can operate it manually and it will cock fine . The lower is an Anderson , the lower parts kit is DPMS . The upper is a complete PSA (Palmetto State Armory) w/ 16" barrel . I have an Anderson lower parts kit ,that I'm thinking of installing . Just to see if that makes any difference . Normally I'd start chasing a short stroke issue , but it ejects and feeds just fine ! Any ideas anybody ?