Pivot pin issues

I have a Colt lower and Colt upper and the pivot pin is having a hard time getting through the upper receiver. It's just impossible to get it through by hand and really hard to get it through with a punch. I have tried different pins and lowers and the issue persists. The same upper on different lowers yields the same results. Different uppers on the same lower work fine. Same with just pushing the pin through the lower without an upper attached. It's definitely the upper.

I can't find any burs or obstructions. My first instinct was the finish in the upper pin area was too thick and to grab the dremel and either:

1. Start on the pivot pin, reducing the diameter. The problem is that if I match the size of the upper, the far side of the lower may not fully engage and the pin won't seat properly.

2. Start removing the finish in the upper's pin area, which I really hate to do to an otherwise perfectly fine upper receiver.

Common sense took over, however, and I figure I'd check the hive mind here before I booger it up.

Any suggestions? Besides a new upper receiver? It's a built upper, so Colt warranty is really not an option.

I had a similar issue with a takedown pin, however it was with just one upper.

I wound up dremmeling the pin to make a flat spot.

I dropped a spare pin in the upper and lower and it suddenly fit. Turns out the pin was inserted 90 off of the proper orientation.

Since the area where the pin is machined to interface with the detent is “flat”, I decided to get the Dremel out and make the part of the pin where the interference was flat. It worked out pretty good.

If you choose to try this, take a spare pivot pin and try dropping it in rotated. I.e 90 degrees out of correct orientation, 180 deg, etc. If one orientation works, take note of where the pin is machined for the detent and Dremel a flat spot.

If it doesn’t work no matter how the pin is rotated, you’ll have to reduce the entire diameter of the pin or modify the receiver.


Edit:

I re-read and your post and noticed I missed the part where you checked and the pivot pin hole upper is the culprit.

Sent from my iPhone using Tapatalk

Take a pin spec diameter class Y or X or XX pin-gauge and see if it fits. If not then there's an alignment issue.
If alignment is off, which could just be an axial issue and not a diameter issue, then I guess the fix is to pass a reamer through it. A task for the avg DIY'er? Maybe, if you have the tools or want to buy tools.
Fixing is part of mating individual parts. Don't like to do it, but sometimes you have to.