AR-15 Upper holes don't line up w/lower pins

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rwl1955

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I finally decided to finish my NES AR and ordered a upper receiver from a Western Ma. gun shop. Picked it up Saturday and when I got home and tried to mate them up a no-go I installed the upper and pushed the front pin in and couldn't get the rear pin thru. I've installed another upper on the NES lower and no problem so it's the upper receiver. Called the gun shop and told them to order me another one and they told me to bring it to show them. I'm not happy. The barrel is stamped BFI, 1-9 twist. Anyone else have this problem?
 
Tolerances between different manufacturers, some of them can be pretty hard to push in initially, I've had some that I had to gently tap in and out with a rubber mallet the first few times till they worked in but I've never had a combination that was so far off you couldn't get the pin thru. Could also be just that is was made wrong.
 
Have you tried setting the rear pin without the front pin engaged?

If you can do that, how does the fit look up around the buffer section of the lower?

I have had a few, that when new where an incredibly intimate fit.
 
I had the same issue with my ar a few months ago. Tolerances were extremely tight. I had to partially put the rear pin in first then push the front pin all the way in. I then took a rubber mallet to slowly tap the rear pin the rest of the way. I then kept pushing the rear pin in and out to loosen the hole. Make sure you use one hand to clamp the upper receiver to the lower receiver

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How far off is "Off" ?
Way off as in you can only see half the pin through the hole or are you a couple of file strokes from glory?
 
I had this happen with a rifle I assembled for my cousin. It was a Spike's lower with a PSA upper. I believe the issue occurs when both parts are at the extreme tolerance range in opposite directions. The one I worked on couldn't be assembled without seriously hammering the rear pin through, and then I was afraid galling would occur, but even if it didn't, you would've needed a hammer and punch to disassemble it, which is unacceptable inmo. I ended up setting it up in my mill and with a 1/4" end mill and milled some clearance on the side that was causing the interference. I only had to remove a few thousandths to get it to work as it should. It was no big deal really, and certainly wasn't worth mailing the upper back, and then waiting for resolution.
 
Upper and lower are no good, I'm incredibly busy but pm me and I'll be happy to get rid of both of them safely. Seriously good luck sounds like they fit..............in my hands
 
I had this problem in a JP .308 once. The factory made it right (by parts replacement, not hackery) immediately and without hassle.

Don't let someone pass off a gunsmith hack like enlarging the hole. You need a new upper and/or lower.
 
I've had this happen so many times I now have a .251 reamer in my tool box. If that doesn't clear up the problem then either the upper or lower are way out of spec. I ream the upper holes to .251 if that doesn't work I do the lower also. If your looking for a tack driver don't do this and buy a high quality matched set. Reaming to .251 is not the best solution. I only do it for non-match rifles.
 
radioman said:
I've had this happen so many times I now have a .251 reamer in my tool box. If that doesn't clear up the problem then either the upper or lower are way out of spec. I ream the upper holes to .251 if that doesn't work I do the lower also. If your looking for a tack driver don't do this and buy a high quality matched set. Reaming to .251 is not the best solution. I only do it for non-match rifles.
Click to expand...

What is wrong with that? The Mil-spec print calls for .251 +/- .001
 
I just went through this with Davidson manufacturing upper. I can't get the upper to close if I install the front pin and try to pivot it close.
I have to install the upper onto the lower and then push the pins in. I don't mind much makes for a very snug fit. I think it's the kinda crappy finish myself.
 
radioman said:
I've had this happen so many times I now have a .251 reamer in my tool box. If that doesn't clear up the problem then either the upper or lower are way out of spec. I ream the upper holes to .251 if that doesn't work I do the lower also. If your looking for a tack driver don't do this and buy a high quality matched set. Reaming to .251 is not the best solution. I only do it for non-match rifles.
Click to expand...

You do realize that the fit between upper and lower has nothing to do with accuracy, right?
 
Terminator03 said:
You do realize that the fit between upper and lower has nothing to do with accuracy, right?
Click to expand...

Not true, if it's rattling like a coconut in a freight car it's not going to do accuracy any good. The rifle needs to fit solid together to be accurate. A small amount of in spec play is no problem. Enlarging the holes beyone .251 is no way to get accuracy. Also I find people building tack drivers don't like Mickey mousing their rifles. Enlarging holes beyond.251 is for people who want to go to the range now not next month when the new lower/upper comes in.
 
7.62x39 said:
What is wrong with that? The Mil-spec print calls for .251 +/- .001
Click to expand...

I've used the .251 reamer about a dozen times now. Not once have I had the reamer drop through the hole without taking aluminum off. So if .251 is in spec I've never seen it. In the real world the holes pick up burrs and other contaminants during manufacturing. I start with a .250 reamer and many times that solves the problem. Other times I'll go to .251 but I will not go any further. If the person wants to go more they can do it outside my shop as I won't be a part of that.
 
Is it possible the lower has one of those tensioning screws meant to take out the slop between upper and lower, and the screw is too far out?


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radioman said:
Not true, if it's rattling like a coconut in a freight car it's not going to do accuracy any good. The rifle needs to fit solid together to be accurate. A small amount of in spec play is no problem. Enlarging the holes beyone .251 is no way to get accuracy. Also I find people building tack drivers don't like Mickey mousing their rifles. Enlarging holes beyond.251 is for people who want to go to the range now not next month when the new lower/upper comes in.
Click to expand...

We aren't talking about making it sloppy as you are suggesting. Enlarging the hole by .001-.003 is hardly going to make a rifle that otherwise would need a hammer to assemble "like a coconut in a freight car". I'm speaking as someone who was a machinist for a decade, as well as a tool and fixture designer for much longer than that. If you are super worried that it's going to affect accuracy, adding one of those silly plastic wedges can fix that, or a tension screw. I still maintain that all things relative to accuracy happen in the upper assembly itself though, with the exception of having a nice trigger versus a gritty mil-spec.
 
Aaron[MA];5477128 said:
Is it possible the lower has one of those tensioning screws meant to take out the slop between upper and lower, and the screw is too far out?


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Click to expand...

That's actually a fair point, although I haven't seen too many lowers come standard with that screw, unless they are custom billet versions.
 

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