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Basic
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Basic
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Posted: 11/26/2012 11:12:48 AM EST
Ive been doing some research and am wondering about Mil-spec lowers. I found a couple of internet discussions about Mil-spec lowers being a little loose fit. Most of these discussions were a couple years old. Is this still the case now?
Do the Mil-spec lowers fit better with same brand uppers? I realize some people on this forum will criticize that the way the lower fits is not a factor to concern yourself with. I understand this point. I have never owned nor shot a Mil-spec rifle.
I am preparing to buy a Mil-spec rifle and am curious about what to expect. Again im not saying that this is an important factor in deciding,I would just like some input from experienced AR enthusiasts. Thank you in advance.
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Link Posted: 11/26/2012 11:20:13 AM EST
A "TRUE" mil-spec lower you will not own without a tax stamp and 20K. So now that we have that established a civi lower one brand will fit slightly different than another. Take for instance an LMT lower vs a Aero Precision lower they will have slight variations not huge but still qualify as a mil-standard like lower.

But most lowers are made close to the mil standard but some manufactures make them with tighter tolerances to allow for tighter fit and no rattle like RRA.
Rattle is not anything to be worried about it can be fixed by an O ring or accuwedge if it bothers you.
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Link Posted: 11/26/2012 11:43:25 AM EST
Most should fit fine with little or no play. like the above poster said, you can buy o-rings or wedges to eliminate any play
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Link Posted: 11/26/2012 11:59:26 AM EST
For the most part, it's hit or miss regardless of manufacturer. And is some cases, it will loosen up over time. Doesn't matter if the lower and upper are the same manufacturer or if they are mixed.
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Link Posted: 11/26/2012 12:16:54 PM EST
It's all about tolerance stacking. If the upper and lower are both at the extremes, you will either get a super tight fight or a really loose one. I just buy multiple lowers and uppers now so I can mix and match. I've only got one set that's so tight I need to use something to push out the pins. The rest are not too tight nor too loose.

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Link Posted: 11/26/2012 12:30:52 PM EST
ok thanks, thats more or less what i was expecting. The functionality of the rifle is the most important. i just didnt want an oh sh!t moment when it seems that it fits a little loose.
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Link Posted: 11/26/2012 1:39:41 PM EST
Oddly, there seem to be almost as many posters complaining about(too) tight fitting uppers/lowers.

As long as the two parts stay together, they're good to go.
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Link Posted: 11/26/2012 1:54:53 PM EST
Originally Posted By KILLERB6:
Oddly, there seem to be almost as many posters complaining about(too) tight fitting uppers/lowers.

As long as the two parts stay together, they're good to go.


As an interesting aside and perhaps as a testament to the adaptability of the AR beyond what most people feel is prudent to do, there have been the occasional reports of people complaining that their AR is functioning, but doing so unreliably, particularly with regards to feeding problems.

Further examination then reveals that the user has in fact mated an SP1-style "big hole" .370 pivot pin upper with a standard .250 pivot pin lower without any shims or bushings, but simply assumed it was "plug and play."

~Augee
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Link Posted: 11/26/2012 1:59:25 PM EST
Originally Posted By EdgecrusherXES_45:
A "TRUE" mil-spec lower you will not own without a tax stamp and 20K. So now that we have that established a civi lower one brand will fit slightly different than another. Take for instance an LMT lower vs a Aero Precision lower they will have slight variations not huge but still qualify as a mil-standard like lower.

But most lowers are made close to the mil standard but some manufactures make them with tighter tolerances to allow for tighter fit and no rattle like RRA.
Rattle is not anything to be worried about it can be fixed by an O ring or accuwedge if it bothers you.


That is why I like RRA Lowers.
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Link Posted: 11/26/2012 3:43:21 PM EST
Originally Posted By Augee:
Originally Posted By KILLERB6:
Oddly, there seem to be almost as many posters complaining about(too) tight fitting uppers/lowers.

As long as the two parts stay together, they're good to go.


As an interesting aside and perhaps as a testament to the adaptability of the AR beyond what most people feel is prudent to do, there have been the occasional reports of people complaining that their AR is functioning, but doing so unreliably, particularly with regards to feeding problems.

Further examination then reveals that the user has in fact mated an SP1-style "big hole" .370 pivot pin upper with a standard .250 pivot pin lower without any shims or bushings, but simply assumed it was "plug and play."

~Augee


OK, you got me: I was being somewhat facetious with my slop comment; should have said as long as an upper and a lower that were meant to be together stay together...
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Link Posted: 11/26/2012 5:43:55 PM EST
Do mfgs give these specs or will it just take some digging to find out?
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Link Posted: 11/26/2012 5:45:20 PM EST
Originally Posted By Augee:
Originally Posted By KILLERB6:
Oddly, there seem to be almost as many posters complaining about(too) tight fitting uppers/lowers.

As long as the two parts stay together, they're good to go.


As an interesting aside and perhaps as a testament to the adaptability of the AR beyond what most people feel is prudent to do, there have been the occasional reports of people complaining that their AR is functioning, but doing so unreliably, particularly with regards to feeding problems.

Further examination then reveals that the user has in fact mated an SP1-style "big hole" .370 pivot pin upper with a standard .250 pivot pin lower without any shims or bushings, but simply assumed it was "plug and play."

~Augee

Will the mfgs have these specs readily available or will it take some digging to find out?
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Link Posted: 11/26/2012 5:51:50 PM EST
I think your bigger problem is finding a lower that's in stock.
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Link Posted: 11/26/2012 7:42:34 PM EST
Originally Posted By Dethtoll:
Ive been doing some research and am wondering about Mil-spec lowers. I found a couple of internet discussions about Mil-spec lowers being a little loose fit. Most of these discussions were a couple years old. Is this still the case now?
Do the Mil-spec lowers fit better with same brand uppers? I realize some people on this forum will criticize that the way the lower fits is not a factor to concern yourself with. I understand this point. I have never owned nor shot a Mil-spec rifle.
I am preparing to buy a Mil-spec rifle and am curious about what to expect. Again im not saying that this is an important factor in deciding,I would just like some input from experienced AR enthusiasts. Thank you in advance.


My .02 - The Industry Forum on AR15.com has several reputable vendors each with their own sub forum. Troll around and read some of the reviews - that's what helped me make my decision as to who's parts I purchased several years ago. FWIW, There are several lower mfg that make "mil spec" lowers that have been mated up with various other mfg "mil spec" uppers without issue, so you really don't have to stick with the same vendor for the upper and lower.

GL.
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Link Posted: 11/27/2012 4:09:49 PM EST
ok i'll give that a shot.
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Link Posted: 11/27/2012 4:18:16 PM EST
Mil-Spec for the gap between upper and lower:

1. With the upper receiver attached to the lower receiver, and the pivot pin and takedown pins in place,
perform the following test:
(a) Apply hand pressure to push the upper receiver as far to one side as possible.
(b) Attempt to insert a 0.020 inch thickness gage between the pivot pin lugs or the upper and lower
receivers.
(c) If the thickness gage penetrates to the pivot pin at all accessible locations, repair by replacement of
the upper receiver (see (b) below) or replacement of rifle is required.
2. If the rifle fails the above test, remove the upper receiver and install a "NEW" upper receiver and perform
the test again.
3. If the rifle now passes the above test, it shall be considered serviceable and continue in use.
4. If the rifle fails the test with a new upper receiver, this failure shall be considered a shortcoming. This
shortcoming requires action to obtain a replacement rifle. Once a replacement has been received,
evacuate the original rifle to depot for overhaul.
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