Well took long enough to start this project but finally got my lower built, the only issue I got was the roll pin isn't going in, it seems like the lower whole is smaller then the pin, anyway no biggie I think I'm about to order a diff trigger guard and I'll deal with that issue then..

Now I have to save some cash and build an upper, I wanted to just buy something cheap so I can have it done, but figured why do this twice I'll get what I really want so it takes longer it will all be worth it in the long run..

I know this has been a blast and it might be might first but won't be my last I'm loving this...

You can "squash" the end of the roll pin slightly to get it started and then tap it on home.

Thanks man I'm gonna try that when my new trigger guard comes in

Roll Pin Punch

Nice work, stunter.  I like to drive that particular pin home with visegrips (pad the jaws with tape), to keep from snapping off the little tab on the far side of the lower receiver.  I would only hammer it home with a punch if I had some kind of fixture to support the lower at that point. - CW

The one I built yesterday was done in haste.
I have a set of punches specifically for the smithing box on a truck headed this way, but couldnt wait.

What i did have was a framing hammer... a dremmel cut off tool mandrel, and about a 3/8" o.d. x 5" long clevice pin with a nice square end.

And the corner of a crafts working bench I built for the Wife... (leather, wood burning, carving, sculpting, etc.. and so on)

The only roll pin that gave me any guff was the trigger guard roll pin like you are having the issue with...
I supported the "ears" on a corner of the bench... held steady and positioned the lil dremmel mandrel with my left hand and kept trying to set the pin in the hole with little taps trying to be careful...
Not so much...
Smack that sucker in there. Once it starts the stress level drops and it goes the rest of the way pretty easy.

Congrats on the first lower!
Between this and modifying my truck im gonna go broke lol