Stag lower and stag upper fitting issues

[jdmtype1]

Hey, today i received my Stag H2 upper. I had built my Stag lower about a month ago, while waiting for the "pig" to get fatter so i get my upper. The front pivot pin snapped into place, but the rear take-down pin get stuck half way. There is no way that i want to pound this pin in, but I'm stumped as to what to do. I even tried oiling the pin.

Also, yesterday i have tried installing my Stag lower on to a Noveske upper, but the pin got stuck half way as well.