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Discussion Starter · #1 · (Edited)
OK...I tried to put my new upper on my last lower this morning...and the take down pin to the rear didn't want to go in all the way...
I got off work thinking to grease the heck out of it, but I tried my beater AR-15 lower on it my little brother put 1000 rounds through on and the take down pin on that one went in with a tight fit. It had some lube on it but it went in all the way.

Thing is both lowers had the same lower parts kits from UTG and both uppers are PSA ones. How did it fit? The SS Beater AR-15 (God I love saying that and having one!) fit with a tight fit on the problem lower the CHF barrel one didn't want to fit on.

Can any one explain to me what happened? I'm glad it happened as now I got all my AR-15s in shooting capability. (Thanks to the back up troy back up sights I found!)

The pin on my last lower would go in 3/4 of the way, my guess it didn't make it through the second hole or leaving part of the take down pin sticking out. The take down pin had to be hammered out side ways with a punch to get it out, I pounded some what with the punch but covered the take down with a thick cloth to see if it would fit, but not to hard and it didn't move at all.

For restoring my back up parts, think I'll go with some UTG back up sights, affordable some people I know who use them say they are great. Or maybe magpul ones, (metal).
 

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I take it you mean take down pin and not detent pin. Anyways tolerance stacking can cause this. One part is at the very high end of tolerance and the other is at the very low end of tolerance. Check to make sure your trigger and safety are installed properly also.
 

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I've cured this issue by running a .250 drill bit by hand through the upper lug that was a problem. Only needed to do it on two and it was the front lug on both. You only need to remove a minimal amount of material.
 

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Discussion Starter · #5 ·
I take it you mean take down pin and not detent pin. Anyways tolerance stacking can cause this. One part is at the very high end of tolerance and the other is at the very low end of tolerance. Check to make sure your trigger and safety are installed properly also.
Um yeah...just testing peoples knowledge base...yeah that's it! Safety and Trigger work fine.

I've cured this issue by running a .250 drill bit by hand through the upper lug that was a problem. Only needed to do it on two and it was the front lug on both. You only need to remove a minimal amount of material.
I was thinking about doing that, I probably will if I want to put it on another upper in the future.
 

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Did you try the beater upper in your lower and visa versa? How do you know the problem is the pin that will not go in? Could be the front hole is off and that would make the rear not line up . I suggest letting someone with a little more experience look at it before going any farther .

Sent from my LM-K920 using Tapatalk
 

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I have had this same issue with PSA blem lowers... little bit of fine grit sandpaper in the holes took off just enough, but thats the risk with blems stuff. :)
 

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I had the same problem when building my 6.8. Aero upper receiver with a sharps rifle co. lower receiver. The upper fit good on my dpms lower I use for my 5.56. It has since broken in but the rear take down pin is a little tight. The sharps lower is a bit out of spec.
 

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Discussion Starter · #9 · (Edited)
Did you try the beater upper in your lower and visa versa? How do you know the problem is the pin that will not go in? Could be the front hole is off and that would make the rear not line up . I suggest letting someone with a little more experience look at it before going any farther .

Sent from my LM-K920 using Tapatalk
Front pin was ok. I just found it odd. I guess it was the tight for the both unused upper and lower, the one used for a year (lower and upper) I swapped them with, worked. The upper went on very tight but it needed only some extra force to get the lower and upper to fit. It is however, is a very tight and nice solid fit.

One thing I did wrong was have my front troy BUS wasn't properly locked down and and it was off by a bit where it was just off enough to throw it off the front to rear sight alignment. I thought my Troy BUS was bad but saw the horrible job mounting it. I'm still investigating who did it. :geek:
 

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I recently had a similar issue with an assembled cosmetic blem lower from PSA. The rear take down pin would go through both sides without an upper installed, but would not go through the far side wall with an upper installed. I tried multiple uppers, 4 total, all with the same issue. When the pin was pushed in slowly, without an upper, it would hit the edge of the hole in the far side wall and there was enough play that it would move over into the hole. Sent it back to PSA and they sent sent a replacement lower, no explanation.
 

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Some things are strange: I hand one lower that both the original 5.56 upper and a 6.8 SPC upper fit but a .22LR upper did not want to go. I did the.250 on the upper rear and it then worked. I have two other lowers that don't want to accept the uppers unless put the uppers on flat (verses front pin then back pin) which then go on easily. Go figure! I discovered this quite by accident and "fiddling" with them.
 
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