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Discussion Starter · #1 ·
I've seem some posts where people say they want their upper and lower to come from the same manufacturer because they feel they will get a better fit.

So, how "modular" are AR parts? Or, more to the point, what parts do I need to make sure are from the same manufacturer? i.e. lower and upper, lower and LPK, etc.

Thanks
 

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If the parts are in spec, then they will fit. Just because the receivers are the same brand doesn't mean they will be a better fit.
 

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Discussion Starter · #3 ·
Thanks!
 

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Use caution when combining two animal themed brands. For example, the DPMS Panther does not get along well with a Stag.

But seriously, one thing to look out for are "non-standard" parts from Colt. You would think that Colt would be the gold standard, but over the years Colt has sometimes changed specs. In order to prevent easy conversion of a semi-auto civilian CAR-15 to a select fire M16, Colt came up with a larger hammer pin and larger trigger pin (0.170) on some production runs. Everyone else uses 0.154. Some Colts also have a different larger pivot pin. I have seen some NIB recent Colts at gunshows and have not been impressed with the upper/lower receiver fit. Some say receiver play is not a major factor in AR accuracy, but I don't like buying rattle traps. All of the Colt small parts and bolts that I have seen have been superb (if you know how to spot the size differences).

One company that takes great pride in their receiver fit is Rock River Arms. Their "regular" rifles and carbines have nice tight consistent fit (putting many other brands to shame) and their match rifles have extra tight fit. They also sell hand fitted upper and lower sets.
 

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CMMG or Tactical Inovations have no fitment problems with LMT.
 

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I like to get like parts because I'm weird like that. No real reason, other then not having to say a bunch of different crap when someone asks me what I've got.

Also, some manufacturers end up looking different then others, probably due to how they coat it. Every once in a while you'll find two companies who's upper/lower just DOES NOT match.
 

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If the parts are in spec, then they will fit. Just because the receivers are the same brand doesn't mean they will be a better fit.
Fit? Yes. Correct? Not so much. My last purchase had (now better) a FCG that was horrible. Under inspection the hammer had a serious "seam" down the center which had left marks down the center of the BCG after the first few shots.

UB
 

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Fit? Yes. Correct? Not so much. My last purchase had (now better) a FCG that was horrible. Under inspection the hammer had a serious "seam" down the center which had left marks down the center of the BCG after the first few shots.

UB
Well, then it sounds like that FCG would have been problematic, no matter WHAT brand of BCG it was paired with.

As long as your parts are in spec, they will be just as good as any other brand.

A great deal of different brands all come from the same factories, and just end up with different stamps/engravings on them.

There is no other difference.
 

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The AR that I recently built, using a Stag lower and RRA flat top upper, is a lot tighter than the Bushmaster that I bought that was built by Bushmaster! ;) I'm extremely pleased with the end product of my build!

W.R., BTW, you were right about that scope's being mounted too far rearward. I just moved it up as far forward as I could....much better! :)
 

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My rifle is CMMG Lower, LPK, and Upper. I just like to keep things the same. Resale value might also be better for a complete AR, rather than a Franken-rifle.
 
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