Hey all-

I bought a PSA AR lower and upper, on a good sale.
Fitting them together is pretty difficult. In order to get the takedown pins to slide through the lugs in the upper, I have to put the lower on the ground, lean on the upper, and then hold pressure downward while sliding the pin through.
To take it apart, I have to repeat the process.

I am not new to ARs. I tried a half-dozen uppers from different manufacturers. All are just as difficult. The PSA upper fits any other lower, without difficulty.

What would you do? Hog out the lugs on the upper until it fits smoothly and decide they are a dedicated pair?
Try different takedown pins from another manufacturer?
Shoot it with some hot ammo and hope it stretches into a more compliant shape?

Full disclosure: I already sent it back to PSA as "out of spec" and they replied "no problem found" and are sending it back to me. I appear to be stuck with it.

Bruce

I would put it in the safe and spend another $50 to get a properly working lower.

Save that for a rainy day when an out of spec lower is worth more than a paperweight.


Edit: If you'd rather make it work, I'd measure the takedown pins, see if they're slightly larger than others you've got, and start sanding them down until the receivers fit well to tell you how far out from fitting they are. That will determine if cutting into the receivers is a good idea, or if you're just stacked up against tolerances and .002" off the diameter of the pins is enough to get it working.

I had to take a wee off the left rear corner of my White Oak NM upper rear pin lug to fit my RRA NM lower. Just a wee.

Not on psa but I’ve met combos that need help. Shoot it first. After that Me if I had parts to swap would figure out if it’s both the upper and the lower or just one. Make sure you try the upper on the lower without the front pin to see if its length or the diameter. Then run a reamer through the part that's a problem till all works acceptable. If investing in a reamer is not possible (you will use it again) then just run a drill through there.At my house the start to that would be 6.5mm but if I needed a letter size they are cheap so I’d just go get what I needed.

This message has been edited. Last edited by: hrcjon,

I’ve got a DPMS that I have to use a hammer and punch to get apart...I just do that.....it shoots great and I use a hammer to get it apart....

quote:

Shoot it with some hot ammo and hope it stretches into a more compliant shape?

I would try that first, 400-500 rounds. It should loosen up at least some and may also leave some wear marks on the tight spots.

Hello,

I’ll give you some good advice rather than tell you how to spend your hard earned money.

Some lowers are tighter than others. It does not mean it is out of speech. My Aero Precision upper would not fit my RRA SBR lower. I knew this going in as RRA builds their lowers to be fit with uppers to get a tighter fit. Try this method. It may seem scary at first but works just fine. I have zero movement between my upper and lower and the more I shot it, the easier the pins became to remove. If your lower is in spec as stated, it should work on a PSA as well.



The following is from RB Precisions website. I use this method during assembly rather than removing metal from the lower receiver or the upper receiver lug. Works every time.

All of the Rock River Arms lowers are an extremely tight fit, they need to be worked in the following way :


For the love of God make sure there is no rounds in rifle and it is on safe, the hammer will need to be back in the cocked position!!! Our lawyers make us tell you that death is possible if this is loaded when you perform this, we like our customers please do not shoot yourself!

1. Assemble the front pivot pin to the upper.

2. Lubricate the rear lug completely with a light grease (best) or oil, lube the inside of the receiver also.

3. Ensure the rear takedown pin is completely out in the open position (detent is holding)

4. Slowly push the 1/2's together, they will stick (THIS IS NORMAL) it will most likely not close completely at first this is normal.

5. Open and close, repeat being careful to keep the halves aligned, do not slam them together but continue to use increasing force to fit together, when almost completely together use a nylon or soft rubber mallet to tap upper receiver into final position.

6. When they are seated (little to no gap between upper and lower) lightly tap the rear takedown pin into place. This will seem scary to a beginner but it is natural for a tight fit.

7. You may see some of the anodized removed from the rear lug at the corners, AGAIN, this is normal.

8. You may have some difficulty separating the upper and lower, with barrel up and rifle unsupported (hanging in the air) grasp the rifle by handguard and give a "smack" to the top of the buttstock, you may need to do this repeatable, usually 5-10 times will do the trick.


The guys at RB Precision are very helpful. THeir website has alot of good info too. Hope this helps!

quote:

What would you do? Hog out the lugs on the upper until it fits smoothly and decide they are a dedicated pair?

quote:

I tried a half-dozen uppers from different manufacturers. All are just as difficult. The PSA upper fits any other lower, without difficulty.

I would modify the lower if it is in fact determined to be the problem.
If the upper fits fine with all other lowers then don't mess with it.
Metal can be reshaped or removed if necessary.
It may require some refinishing though.
Good Luck

Somewhere long ago I came across the advice to insert the rear pin first before doing the front. It worked for me on a couple of tight fitting uppers. Especially if you use an 'accua wedge'.

I wouldn't mess with it. If it fits, you're GTG, regardless of difficulty. I'd rather have an extremely tight fitting receiver set than some of the sloppy combo's I've handled.

Shoot it and it'll loosen up to "juuust right"....

quote:

Originally posted by m499:
I wouldn't mess with it. If it fits, you're GTG, regardless of difficulty. I'd rather have an extremely tight fitting receiver set than some of the sloppy combo's I've handled.

Shoot it and it'll loosen up to "juuust right"....

This.
I'd at least shoot it before you do anything.

There was an old shooter that wrote for several gun magazines (can't recall his name) that said something to the effect of "any rifle that is loose in the stock will never be as accurate as it could be."

For this reason I bought a JP Enterprise pin that after you insert it, you tighten it with a allen wrench to pull the upper and lower tighter together, it improved my groups of my varmint gun by at least a 1/4".

I had a badly matched upper/lower once (CNC grease gun mag lower and a wonky Oly upper) that I thought was an alignment issue, but in fact it was a lower with a "high shelf" and an upper with an overly long rear lug. They were hitting before the holes could line up. Ended filing off a little from the bottom of the lug.

Have also had to elongate the rear pin hole on a lower to solve a similar problem. Gunsmithing rule #1 is "always alter the cheaper part first". In your case oddly enough, that might be the lower! But I can't think of a real good way to alter the lower, so I wouldn't. You might try chamfering the right side of the lower's real pin hole if it isn't already, that might help get it started.

We are talking PSA parts here, not a high end varmint gun or something else you might actually try to make a pain in the a** to maintain. There is nothing magic about fixing this. You can ignore it and then eventually the steel parts will wear the aluminum parts and it will get better. But I don't see any reason to have an upper and lower that can't be disassembled without special actions or tools. The answer is amazingly simple. Find the part or parts that are causing the interference and adjust them. Holes can be reamed, lugs can be filed, etc. etc. The idea that you have to have a hammer and punch to see exactly what's up with your jammed gun at the range would not be exciting to me.

Yep, do some measurements and a slight adjustment is what I’d do.

I never would have done this a few year ago, but after blending the grip and mag well on a $1600 pistol, I’d just fix your AR.

Lots of people pay lots of money to get very tight fitting receiver sets. Go shoot it.

My new Aero upper was a tight fit on my older Bushmaster lower, as in the pins didn't want to go in. I would have to lightly tap the pins in with a nylon hammer and use a bullet or a punch to get them out (especially the front pin). I've fired about 300 rounds through it now and it's loosening up some, to the point that I can usually operate the pins by hand now.

Give it a little time, and if that doesn't help then I'd second the recommendation to replace the lower and save this one for a time when they're a hot commodity again and somebody will be happy to get any lower they can lay their hands on.

quote:

Originally posted by 1KPerDay:
Lots of people pay lots of money to get very tight fitting receiver sets. Go shoot it.

"Tight" fitting receivers that are done right have concentric takedown pin holes. It comes from controlling the dimensions on the two halves and ensuring the lugs on the upper are the correct width and height, along with the pockets on the lower.

I have receiver sets that are very tight fitting. The pins still pop out with ease. Mega/Zev and the brands they OEM for are one of the receiver companies known for this tight fit.

This issue in the OP is not the same thing. For the takedown pins to be that tight there's a mismatch in the bore concentricity between the receivers. From the info in the OP it's likely in the lower. It could be the takedown pin bores cut too low, or crooked, or maybe the takedown pins are too thick, etc. Or a combination of tolerance stacking (which, according to TDP, shouldn't be a thing)

PSA has returned bad components as "in-spec" to people. Independent inspection has revealed issues with tolerance, assembly procedures, materials, etc. The fact that PSA said this receiver set was "in-spec" means absolutely nothing.

And FYI - the cheapest part that should be modified first, in my opinion, are the $2 takedown pins, not the receivers.

My two cents....( and that's what it's worth )….I'd go shoot it a bunch and if it was still too tight I would buy a couple of pins from different companies ( they're cheap) and try them out until I found one that fit better.
I would try hard to avoid drilling or "hogging" out holes on a gun. JMO...

PS: I have seen pins that were not quite straight....fwiw

Looks like I will just give it a 500 round break-in period, like it's a custom 1911

Thanks for all the replies.

Bruce

Like you just said, I would leave it alone for a while. If "I" had to do something about it. I would take a file to the take down pin/pins and not the upper and lower receiver. The take down pins are cheap and easily replaced.