No it looks like it’s hitting on the left hand side of the rear take down post on the upper.
No, I literally got the lower today from palmetto and it’s for build, I only bought the complete lower because it had the geissele trigger for about 10$ more than the trigger itself.
I would send it back if you can’t try another upper.
Oh I tired it on both my uppers. Both fit like that.
Push it down…something in interferring. Is the grip screw too long or is it hitting the safety?
Try pushing in the rear pin first follwed by the front pin. I have a couple tight fitting lowers and sometimes switching the order of the pins helps for some reason.
Neither of those seemed to help. It looks like the uppers I have aren’t lining up. I’m hoping the slick side colt upper I have coming for my xm177ish build fits. Fingers crossed.
I have the same exact issue as yours with the same upper and lower, with rear pin holes not lining up in the same exact manner and hitting the left hand side of the rear takedown post. My front pins line up perfectly too. What was your solution? This is my first AR-15 so I have no idea what to do.
Take the bcg out and see if it will close. Rear take downs are notoriously tight the firat couple of times.
Took BCG out and tried still didn’t work, but taking out the front takedown pin allowed the receiver to sit flush on the holes with the rear takedown pin. I still can’t seem to hammer it through for some reason. and when I look at the front pin when the upper is perfectly aligned with the lower and the rear pin, the front pin holes are off to the right by about 1/64th of an inch (measured using punches)
Was this a whole gun you purchased o4 did yiu buy the upper/lower separate.
Also, do you have another lower and upper that you can swap? Or have a friend that has one?
Welcome to the forums @pbfastswimmer 
Either my jackolantern or the ghost lower, was tight like this…….don’t recall which one. I used a drill bit that was just undersized as a reamer and it just took off enough of the coating (NOT aluminum) for the pins to pass through. Then just worked them back and forth enough til I was happy with it somewhat tight. Shot a few hundred rounds and it’s good.
it was a separate upper and lower, but both from PSA. The upper is the PSA 16" MID-LENGTH 5.56 NATO 1:7 NITRIDE 13.5" LIGHTWEIGHT M-LOK CLASSIC RIFLE KIT WITH MBUS SIGHT SET - 5165448515. The lower is the PSA M4A1 STRIPPED LOWER RECEIVER.
Don’t have any other receivers I can try with since this is my first AR-15, nor do I have friends with any, but do you think I should take it to a gunsmith or do you think I should contact PSA first?
Contact PSA. Without others to test we wont be able to see if one is out of spec.
Hey guys, I had the same problem and I found that it’s the buffer tube at fault! If you unscrew it 1x the upper and lower will fit as it should. It does lead to another potential problem though. Now the buffer tube won’t latch to the retainer pin. Not sure how big of a deal this is, as this is my first AR, but I thought about grinding down the buffer tube. I have to find a metal grinder though, but I think it should work. Hope this helps.
Welcome to the forums @dwertle
Having the same exact problem with my 80% receiver that i built.
Tried matting it to an aero and psa upper and no magic. Tried pairing my older psa upper and lower to any of my other uppers and its flawless.
Im preety sure the pins are smaller on the older rifles. should i attempt a sand down? I dont mind trying, i can get new pins. And im learning to become my own smith but i wouldn’t want to void warranty either.
Since you have a different lower that fits, did you measure the pin diameter on that lower vs the 80% lower to see how different they are? I’m not aware that the diameter ever changed on an AR15 although differences in tolerance among manufacturers probably exists. I never had a problem swapping any of my uppers and lowers except for a couple of raw NFA 80% lowers that needed the radius where the deck meets the buffer tower reprofiled before a non- NFA brand upper could close on it.
Welcome to the forums @Hobbies77
AR-15 pin diameter and holes should be 0.250”. Tolerance like + 0.003 on holes, and -0.003 on pins (IIRC). I cannot recall the AR-10 diameter off the top of my head, but it’s larger.
If the buffer or buffer tube isn’t interfering, and the profiles match, look to the pocket where the takedown pin boss fits.
I had a batch of Anderson lowers that had been machined a little too far forward, and a MilSpec upper would not sit down-into the pocket. Irritating. It was just the back-corners that dragged a bit, but I had to relieve them, making another step I wasn’t counting on.
If you find that is the problem, and you have no way of milling the pocket, probably just filing the offending corners off the boss on the upper would “fix” it, and not affect the ability to put it on another lower.
It goes without saying (but I will anyway!) - this should be done only as a Last Resort - when you are Absolutely Certain that is the problem, and you have no other Recourse to fix it.
I’m NOT saying this is the problem - merely that it’s a POSSIBLE Problem.
I would look to the depth of the Buffer Tube first…