Hi, i’m new to ar’s and i just got my upper today. I’ve had the lower for a while and when i tried to put the back pin in, it wouldnt go all the way through. I think I need to file out some material in the upper pin hole. Is this correct? And after i do the filing, do i have to put something on the exposed metal? Thank you in advance.
Oh yes, here are some crappy phone pics 
Here’s what my pin looks like now:
Identify the makers of the components for best advice.
YHM upper and a Tactical Innovations lower.
Do you have any friends with uppers you can try on your lower?
I found it guys :o i told you i was a noob. The TI lower has a nylon tipped screw that tightens up against the upper to stop any wobble. The screw was up about a quarter turn to far!
I would take the screw out. It doesn’t belong there in the first place, and can only cause problems.
I agree entirely.
Wow! What will they think of next?