When I put my AR 9MM together a few weeks back I used a PSA 9MM upper with the 8" barrel and the new hybrid bolt. I used a Spikes Tactical lower.
The two receiver halves would not close to allow the take down pins to insert. I had to removed some metal from the center of the bullet guide at the front of the lower as the bolt was making contact there. The bottom of the bolt, that picks up the next round from the magazine and shoves it into the chamber, didn't want to remove metal from it. After that grinding/sanding/polishing it worked fine.
I blamed it on using an upper from one company and a lower from another company.
My nephew got a hankering for a similar AR pistol and PSA happened to show 9MM complete lowers about 8 or 10 days ago and he ordered one.
We began to look around at all the different parts/pieces required to build and upper. We hadn't got around to deciding what he wanted or ordering anything yet when PSA showed complete uppers (identical to mine) for sale and he ordered one.
The lower came in first, the upper came in today. He brought them over to show them to me and realized the upper and lower would not go together. We checked and saw marks in the finish on the bullet guide where the bottom of the bolt was hitting it when he tried to close the two receivers together to insert the take down pins.
We had to do the same thing to it. Remove some metal right in the middle of the bullet guide.
So, it's not the mixing of uppers and lowers between manufacturers, it's something about the PSA hybrid bolt and how if fits/works with the lowers.
FYI for anyone thinking about the PSA 9MM AR upper/bolt. It's not hard to fix, but it will need some work.
