nheiny13 Posted April 6, 2014 Share Posted April 6, 2014 I have an upper and lower that fit VERY tight. When I try to mate them together the rear takedown pin doesn't go in since the upper can't come all the way down due them both being "oversize." They butt together at the bend at the back near the extension tube, preventing it from going down futher. What is the best way to fit these. The upper only needs to come down a couple of thousandths. Should I file down the areas that butt together or just file on the takedown pin hole in the upper making is slightly oblong so that the pin will fit. I'm leaning towards filing the pin hole. What do you guys think? Thanks Link to comment Share on other sites More sharing options...
Dan Sierpina Posted April 6, 2014 Share Posted April 6, 2014 I'd rather remove material from the radius on the upper. Leave the hardcoat for the pin. Can you tap the takedown pin in, with a small plastic hammer? Link to comment Share on other sites More sharing options...
Jaxshooter Posted April 6, 2014 Share Posted April 6, 2014 I would do the fitting on the upper. Link to comment Share on other sites More sharing options...
mpom Posted April 6, 2014 Share Posted April 6, 2014 I would look for a couple of extra pins, to find one that will allow go in completely without altering the receivers. If the interference is only a few thous, the variation in pins should allow you to find one slightly undersized and make it work. Link to comment Share on other sites More sharing options...
nheiny13 Posted April 6, 2014 Author Share Posted April 6, 2014 I'd rather remove material from the radius on the upper. Leave the hardcoat for the pin. Can you tap the takedown pin in, with a small plastic hammer? No it's too tight to even do that Link to comment Share on other sites More sharing options...
nheiny13 Posted April 6, 2014 Author Share Posted April 6, 2014 I would look for a couple of extra pins, to find one that will allow go in completely without altering the receivers. If the interference is only a few thous, the variation in pins should allow you to find one slightly undersized and make it work. It's actually probably closer to a few hundredths since I can look into the pin hole and see that the holes don't line up Link to comment Share on other sites More sharing options...
BitchinCamaro Posted April 6, 2014 Share Posted April 6, 2014 (edited) Like .02, or more like .07"? If you flip the assembly upside down on a table or bench, and put plenty of pressure on the trigger guard/grip area, are the holes in the thousandths range or still in hundredths? is the interference in the buffer area still in the range of thousandths? If it is, instead of filing or sandpaper, you may want to lap them together with a fine borepaste. Lube the front pin with plenty of oil, smear the interfering surfaces with JB or Iosso paste, and just pac-man the upper and lower receivers together a few hundred times until those surfaces mate perfectly. If the interference in those surfaces (just at those surfaces, not at the takedown pin misalignment) is much more than a few thou though, you may need heavier duty solutions. Edited April 6, 2014 by BitchinCamaro Link to comment Share on other sites More sharing options...
Mark Gale Posted April 7, 2014 Share Posted April 7, 2014 I would look for a couple of extra pins, to find one that will allow go in completely without altering the receivers. If the interference is only a few thous, the variation in pins should allow you to find one slightly undersized and make it work. It's actually probably closer to a few hundredths since I can look into the pin hole and see that the holes don't line up Are the upper and lower from the same manufacturer? Link to comment Share on other sites More sharing options...
jriggs Posted April 7, 2014 Share Posted April 7, 2014 I would take it to my gunsmith...can't see a basic upper/lower fitting costing more than $50 Link to comment Share on other sites More sharing options...
BBJones Posted April 7, 2014 Share Posted April 7, 2014 I would look for a couple of extra pins, to find one that will allow go in completely without altering the receivers. If the interference is only a few thous, the variation in pins should allow you to find one slightly undersized and make it work. It's actually probably closer to a few hundredths since I can look into the pin hole and see that the holes don't line up Are the upper and lower from the same manufacturer? This? What is the setup you are using? Is one part known to be in spec 99.99% of the time? I have never needed to mod either and usually you get sloppy fit vs so tight they dont fit together. I would attempt to try your upper and lower in different combinations. If I ever have one that seems tight or loose, I try them with a different upper/lower to see which part is the problem. The more you have to compare to the better. For a no non-sense and firm but not overly tight fit, I have settled on VLTOR MUR uppers on a quality milspec forged lower (LMT, DD, BCM, etc.). Beautiful thing when you know your build will go smooth before you even start. IMO a tight upper/lower fit is less important than a stiffer upper (ie MUR). Link to comment Share on other sites More sharing options...
nheiny13 Posted April 8, 2014 Author Share Posted April 8, 2014 I would look for a couple of extra pins, to find one that will allow go in completely without altering the receivers. If the interference is only a few thous, the variation in pins should allow you to find one slightly undersized and make it work. It's actually probably closer to a few hundredths since I can look into the pin hole and see that the holes don't line up Are the upper and lower from the same manufacturer? This? What is the setup you are using? Is one part known to be in spec 99.99% of the time? I have never needed to mod either and usually you get sloppy fit vs so tight they dont fit together. I would attempt to try your upper and lower in different combinations. If I ever have one that seems tight or loose, I try them with a different upper/lower to see which part is the problem. The more you have to compare to the better. For a no non-sense and firm but not overly tight fit, I have settled on VLTOR MUR uppers on a quality milspec forged lower (LMT, DD, BCM, etc.). Beautiful thing when you know your build will go smooth before you even start. IMO a tight upper/lower fit is less important than a stiffer upper (ie MUR). It is a Seekins IRMT-3 Upper and a Templar Armament billet lower. I would hate to file on and ruin a $300 upper, so now i'm leaning towards filing the lower to make it fit. And as far as different pins go, I don't think that will work as you can see from the picture that there is quite a bit interference. I also used a sharpie on the lower, Pac-man'ed them several times and you can see where the interference is. Link to comment Share on other sites More sharing options...
nheiny13 Posted April 8, 2014 Author Share Posted April 8, 2014 pics Link to comment Share on other sites More sharing options...
Finbox Posted April 8, 2014 Share Posted April 8, 2014 Does this lower work with all your other uppers and your friends uppers? If so send the upper back to seekins Link to comment Share on other sites More sharing options...
BBJones Posted April 8, 2014 Share Posted April 8, 2014 Does this lower work with all your other uppers and your friends uppers? If so send the upper back to seekins This is what I was getting at. Try the lower with other uppers and the upper with other lowers. You should see a trend as to which one does not fit. Link to comment Share on other sites More sharing options...
nheiny13 Posted April 8, 2014 Author Share Posted April 8, 2014 Well I ended up using the dremel to lightly and slowly take material off the back and the radius of the lower. They fit pretty good now. Link to comment Share on other sites More sharing options...
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