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Posted: 3/29/2012 4:48:34 PM EDT
Okay, so I finish my lower and test it 6 different ways to Tuesday, everything looks good. I purchased the upper from Rio Grande Arms (nice people, very helpful). So I go to mate the upper and lower and I can't get the take down pin to go through the upper. Looking through the hole, there's like a millimeter or less of metal where the upper should have just a hole. This is also evidenced by
the scuff marks on the upper resulting from my trying to push the pin through. They just won't meet. I've checked to see if there's something in the way, I've also tried without the BCG and they won't mate to allow the take down pin to go through then either.

It's not the hole size, that works when I took the lower apart to make sure. The pin goes through.

The lower is an Aim Surplus. The upper is Daniel's Defense.

I'm a complete noob here, so any ideas would be appreciated.
Link Posted: 3/29/2012 4:54:14 PM EDT
If the upper fit and the pins went through the upper and lower before you assembled it you might check this.

If you screw the stock tube in too far and it goes past the top inside edge of the lower it can cause the upper not to close all the way and the rear pin does not want to push through..
Link Posted: 3/29/2012 4:56:54 PM EDT
Here's one thing to try. Put a drop of nail polish (hers not yours) in the lower where the rear lug would hit. Close and open the upper and see if there's contact between the upper and lower. I would be surprised, but maybe. The upper and lower you have should be just fine.

I've never had to adjust the takedown or pivot pin holes in an upper so if that's necessary I'll leave it up to the experts to recommend alternatives.
Link Posted: 3/29/2012 4:59:04 PM EDT
Is it a complete DD upper... Or a stripped upper you were told was made by DD?

Aim surplus does not make lowers... You bought it from them? Brand?

It sounds like a tolerance stacking issue... One or the other is out of spec or they are both on opposite ends of the spec. Is rio grande a local outfit? Can you go back there and try swapping around uppers/lowers to indentify which part is the more likely suspect?

It happens occasionally... Random bad luck in the tolerance matching game... Ideally you would want them to swap your upper with another one as this will be easier and less paperwork... But if your lower is the out of spec part then contact Aim and I'm sure they will make it right.
Link Posted: 3/29/2012 5:24:35 PM EDT
I think I would try the upper and lower on other name brand lowers and uppers to try and get a handle if one part is out of wack or if it is just
tolerance stacking.

I assume from your description you are putting the front pin in and then the parts close but the rear pin doesn't clear with the hole?
other than the pin how do the two parts seem to fit?

It could be partly the front pin is whacked also

If the upper and lower seem to mate except for the hole I would go at the hole with a chain saw file. That would be the rear hole in the upper that is hidden as soon as you close the two halves. I am a function guy more than form. You might be surprised how little you need to remove to get things going. Cover any bare metal with poor mans anodizing. (sharpie!
Link Posted: 3/29/2012 5:35:34 PM EDT
I just assembled a new upper using a Daniel Defence upper and it is F'en tight on all of my lowers....not good fit tight but @#%^&& tight at the pivot pin. I wonder if they have a QC issue?
Link Posted: 3/29/2012 5:41:45 PM EDT
Originally Posted By GUNGUY148:
I just assembled a new upper using a Daniel Defence upper and it is F'en tight on all of my lowers....not good fit tight but @#%^&& tight at the pivot pin. I wonder if they have a QC issue?


I don't know if BCM uses the same upper manufacturer as DD does, but I just sent my BCM back because it also would not mate to several of my lowers. It came close on the S&W lower, but I still did not feel comfortable hammering the pin that hard so I contacted them about it. And don't get me wrong. I have had hard difficult to insert pins before, but this was a bit too much.
Link Posted: 3/29/2012 5:48:08 PM EDT
Originally Posted By H53EXPERT:
Originally Posted By GUNGUY148:
I just assembled a new upper using a Daniel Defence upper and it is F'en tight on all of my lowers....not good fit tight but @#%^&& tight at the pivot pin. I wonder if they have a QC issue?


I don't know if BCM uses the same upper manufacturer as DD does, but I just sent my BCM back because it also would not mate to several of my lowers. It came close on the S&W lower, but I still did not feel comfortable hammering the pin that hard so I contacted them about it. And don't get me wrong. I have had hard difficult to insert pins before, but this was a bit too much.


Interesting....Also there is no doubt in my mind that it will only get worse as the panic sets in and factories massively ramp up production. I know last go around some shotty machining was commonplace
Link Posted: 3/29/2012 6:01:27 PM EDT
[Last Edit: 3/29/2012 6:02:00 PM EDT by RGIFFOUR]
Try tipping the upper forward and up abit.. once you get the pivot pin in totally the upper should tip back and align with the rear takedown..

Try without the BCG and sometimes the hammer being UP (not cocked) may cause issues with hitting the BCG..

I have one from them from January and it was a little tight.. they were using BAF/FN forged uppers from Ranier at the time.. (has a square box on the side)..

Mine was a DD barrel assembled into the upper receiver for like $470.. (like yours probably)..

Try working the front pivot pin in and out on your lower also.. mine was sticking as it was new build as well on a PSA lower...

Link Posted: 3/29/2012 6:06:21 PM EDT
It's called tolerance stacking.

It's a common occurrence but very frustrating.

Sometimes it's a matter of trial and error until you get a good fit.

Ironically, the "tight fit" is more out of spec than a loose or easy fit (meaning that both upper and lower are very close if not dead on the blueprints)
Link Posted: 3/29/2012 7:58:00 PM EDT
Thank you all.

Tomorrow, I'm going to pull the buffer tube back just a bit to see if that's the problem. Then I'll try nail polish as suggested as it can't hurt. Then I'll call aim and Rio Grande and talk to each.

I'll let you know the results.

Jim
Link Posted: 3/29/2012 9:51:46 PM EDT
[Last Edit: 3/29/2012 9:53:55 PM EDT by Obo2]
if your buffer tube was screwed in that far wouldn't the buffer fly out because the pin would have to be entirely pushed in?
sometimes after you get the front pin in you just got to try and wiggle the upper around on the lower to get the takedown to fit.
I hate cs i would just bust out the file if it wouldn't fit. Maybe just make a smaller pin that way your not filing a more expensive part.
Link Posted: 3/30/2012 2:03:08 AM EDT
if your buffer tube was screwed in that far wouldn't the buffer fly out because the pin would have to be entirely pushed in?


No. You would be surprised how little the tube has to be screwed in past the lower when it begins to interfer with the upper closing.
Link Posted: 3/30/2012 2:34:50 AM EDT
I ran into a similar problem on a build back about a year ago. It turned out that the rear lug on the upper was machined just barely out of spec. I ended up using a file and slightly filed the sides of the lug, not the bottom, until it fit. Now that upper/lower is the best fitting matched pair I own and fits like a glove. I touched up the lug with an aluminum black pen from birchwood casey and the rest is history. Just make sure where it is a tight fit before you start filing (not grinding, it won't take much filing to correct)
Link Posted: 3/30/2012 6:06:31 AM EDT
J3 was correct. I unscrewed the buffer tube one rotation and the upper and lower mated perfectly. And the buffer is still snugly in place. Thank God something told me not to use loctite or this would have been a bigger issue. Thank you, J3. And thanks to everyone who replied. I am now the proud owner of my first black rifle. I've got a couple of things coming in the mail to put on it, so no pics for now. But I will post them in another thread as soon as they arrive.

As to addictive? Yep. I'm already trying to decide on the caliber of my next one!

Jim
Link Posted: 3/30/2012 8:46:31 AM EDT
Originally Posted By EvilPooky:

As to addictive? Yep. I'm already trying to decide on the caliber of my next one!
Jim


All of them.

I'm glad to hear it was something simple. I'll have to remember that one.
Link Posted: 3/30/2012 10:31:20 AM EDT
It's always nice to have a simple fix for our issues. I was lucky on my recent build. The upper and lower fit perfectly, not even room for an accuwedge to fit in, absolutely no wiggle.
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