quote:

Originally posted by RNshooter:
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.

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

It's unfortunate that you have the upper/lower fit issue and PSA won't deal with it. IMO the lower's machining is out of spec, and there's really no way around that.

The 500 round break in works for tight 1911 because the slide and frame rub against each other during cycling. This rubbing slowly polishes the high points of contact.

No such sliding action exists while cycling an AR15. The only cycling action you will be doing is pushing the pins in and out. However, it is possible that the recoil process might expand the holes in the receiver{s) or bend the pins. I wouldn't cycle the AR in hopes that something in the fit changes. I would take the AR to my trusty gunsmith, and see what he recommends.

We have steel pins impacting a (softer) aluminum part. Over time recoil will definitely improve the situation. But there is no reason for waiting what might be a long time. The tools to fix this are readily available, cheap and easy to use. I wouldn't tackle the takedown pins as was suggested(a steel round part hard to modify) but you could measure a few to see if there is a decent variation of size and pick one on the small size. Grab a reamer (or appropriate drill) or get your gunsmith to do it for you and adjust the the thing). I've had to do it a number of times.

If you built the lower - check to see that the buffer tube is not putting pressure on the upper receiver. IE, back the buffer tube out one thread and re-tighten the castle nut. Then check the fit again.

Always willing to learn. But in a properly assembled lower the buffer tube is located by the need to hold the buffer retainer. There is simply no way for the buffer tube to put pressure on the upper.

quote:

Originally posted by hrcjon:
Always willing to learn. But in a properly assembled lower the buffer tube is located by the need to hold the buffer retainer. There is simply no way for the buffer tube to put pressure on the upper.

The buffer retaining pin's hole can be placed too far forward or be oversized. Just as placing it too far back can lead to a short installation of the receiver extension and allow the gas key on the BCG to strike the lower receiver, often resulting in broken gas key screws.

Or, as you noted, the lower can be assembled incorrectly.

The number of out of spec lowers in people's hands is quite larger than you'd expect.

I am not a machinist or a gun smith but this is my .02: like others have said, I’d shoot it some and see if anything loosens up. Next I’d try some lapping compound on the holes and see what that does. I think I’d try that before a reamer or drill...

SB

quote:

The buffer retaining pin's hole can be placed too far forward or be oversized.

OK never heard of that ever (oversized wouldn't matter) but easy enough for RNshooter to see if the buffer tube is threaded so far into the lower the upper could hit it?

It is a complete lower assembled by PSA. The extra effort to squeeze the upper and lower together is more of an annoyance. I sent it back to be checked mostly out of an overabundance of caution, this being a bangstick, and all.

My comment about a "500 round break-in period like it's a custom 1911" was meant to be ironic, being that this is an extremely down-market AR. Shooting it shouldn't make it "wear in" but I'm not losing a whole lot of sleep over it. Heck, I may mortar it on the ground a half-dozen times to see if that helps.
Lowers are cheap enough. Pity they didn't want to fix it.

Bruce

quote:

Originally posted by hrcjon:

quote:

The buffer retaining pin's hole can be placed too far forward or be oversized.

OK never heard of that ever (oversized wouldn't matter) but easy enough for RNshooter to see if the buffer tube is threaded so far into the lower the upper could hit it?

Oversized holes can let the retaining pin escape forward of the lip of the receiver extension, or require the extension to be installed deeper than it should be. This is the type of tolerance stacking that the TDP is designed to eliminate, but as we all know "mil-spec" is now just a phrase and no guarantee of a company actually following specs.

Yes, it should be apparent if the receiver extension is causing an issue with fit. You'd also notice the tail of the carrier contacting the top or face of the buffer more than it should. Depending on exact part geometry this might not stop the halves from coming together if the carrier can still push the buffer out of the way off fillet/chamfer edges.

Retaining pin holes that are too far back also have a tendency to cause broken retaining pins, as the buffer contacts the pin during operation (which it should not do). It's always a good idea to inspect the face of your buffer for damage that would result either from the retaining pin or (more commonly) a burr on the tail of the carrier from machining the retaining pin slot.

I’ve owned at least 20 AR15 rifles, most of them builds with different manufacturers lowers and uppers. Tight pins that require a punch and a hammer are unacceptable to me. These are gunsmith builds and sometimes need some gun smithing.

Put the front pin in, remove the rear pin completely out of the gun, snap the two halves together, use a flashlight and look into the rear take down pin hole. It will be plainly obvious that you have some tolerance stacking issues and you can easily see that a few thousandths worth of aluminum in the upper are protruding into the hole. A round file and 4-5 strokes, just enough to knock off a tiny fraction of metal, and you’ll be able to snap in a rear take down pin with proper finger tight pressure and no tools needed.

Me personally? It’s a 5 minute repair, easy to fix, and makes the gun much more enjoyable to know that everything fits and functions perfect without tools needed for disassembly. The AR15 in my uses should be easily field serviced with no tools needed for take down. If you want to build a precision varmint type build, then living with ultra tight pins might be preferable.

If it goes together with some hand pressure I wouldn't call it out of spec.

I helped a buddy with a build last week using Aero upper and lower, with all the small parts coming from Aero.

The pins are quite tight. That is what he wanted. I prefer them to be easy to take apart. In my experience with normal use, it doesn't take very long for pins to become quite easy to slide in and out. Fresh anodizing can be a little rough on somewhat sharp edges.

Put a little dab of grease on each pin and before too long I suspect they will slide easily.

I'm in Las Vegas. I can take some measurements if you think it will help you figure out where the interference is before adjusting anything.

quote:

Originally posted by vinnybass:
I'm in Las Vegas. I can take some measurements if you think it will help you figure out where the interference is before adjusting anything.

Here is the only correct recommendation. Without knowing where the interference is there is no way of knowing what to fix.

quote:

Originally posted by vinnybass:
I'm in Las Vegas. I can take some measurements if you think it will help you figure out where the interference is before adjusting anything.

Thanks, Vinny. I am waiting for it to be returned. I will definitely shoot it a bit before breaking out the files. I appreciate the offer and will reach out, if I decide to go that route.

Bruce