PSA 300 upper not fitting

[Erni]

I picked up a 300 rifle upper on the board a while back. Got to fitting it on a lower and no go. Out of several lowers it would fit only on one and badly at that. It looks like the rear pin will not go in. Either the upper is machined incorrectly around the rear lug or the hole is too high as th pin on one lower left a small indent below the hole.
I think it is this upper as the other lowers and uppers interchange.

How to measure this? Sugestions on what to do?

[henpecked]

Pm sent

[Great-Kazoo]

Take a fine tooth file to the bottom of the rear lug. W/out pictures sounds like it's sitting too high in the lower. Would not be the first (or last) upper that fits like this.

[SA Friday]

Take a fine tooth file to the bottom of the rear lug. W/out pictures sounds like it's sitting too high in the lower. Would not be the first (or last) upper that fits like this.

Maybe, but I wouldn't take a file to it just yet. It could be mis-aligning or binding in one or more different areas.

Either bring it in to Bowers (Me and Rob) or B&P tactical (Bert) and we can look at it, or post lots of picks. The lower doesn't have a tension screw in it that needs to be lowered?

[Erni]

Hen, will take you up on offer if I cant figure it out by weekend.

GK, will check the lug length and see if contact occurs.

[henpecked]

I can measure everything for you. Surgury tomorrow but should be back by Friday.

[Erni]

Quick update. Looking at it right now.
I think PSA left fillets on the rear lug and they are resting on the lower and not allowing the hole to be low enough. I can see the hole is a little too high in the rear with the front pin in.
Can't measure very precisely as I dont have a gage pin and only a set of punches and calipers, but the rest of the dims seem about the same.

Thoughts?

RRA


PSA

[Erni]

One more thing. The rear hole in PSA is at .249"D. The hole in the RRA is .255"D.

It could be the PSA hole is undersized and combined with the fillets and maybe it is up too high. If all 3 combined the true position may well be beyond tolerance.

[Erni]

Special thanks to henpecked for helping out.
We cut the radius down and it got close. Ended up reaming the hole to open it up a bit and that did the trick.

Now I need a bcg and some ammo...

[kidicarus13]

Henpecked is a good guy. Always willing to reach out to the community and help.