AR15.Com Archives
 Lower Receiver ? regarding MIL-Spec and Commercial
eltice  [Member]
3/5/2011 8:50:19 AM
Good morning all. I am new to building AR-15's, so if this sounds like a dumb question, please go easy on me. I tried a search, but couldn't find anything, I may have done it wrong though.

I understand (at least I think I do) the difference(s) between MIL-Spec vs Commercial, but how do I know which receivers are what? I have looked at DPMS and RRA sites, but they don't clearly state what specs their receivers are machined to. Again, I may have missed it somewhere, but I even tried an internet search and was unsuccessful.

Thanks for any help!
Eric

edit to add: Main reason I am wondering is I see that there are MIL-Spec AND Commercial Buffer Tubes???
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NoZombies  [Team Member]
3/5/2011 8:53:33 AM
they should all be the same spec. RRA is a little tighter near the rear takedown pin
eric10mm  [Team Member]
3/5/2011 9:02:23 AM
Technically, no semi-auto lower is ever "milspec", but...

DevilPig  [Team Member]
3/5/2011 9:20:13 AM
Don't get too caught up on the whole milspec vs commercial thing...

Really the only things that are drastically different are the buffer tubes. If you have a milspec tube it will only accept milspec stocks and vice versa. The lowers will accept either commercial or milspec tubes. Not really a difference there.
Adirondack1  [Team Member]
3/5/2011 9:56:20 AM
Mil-spec in what regards?
Materials?
Surface finish?
Obviously the interior dimensions are different (I won't go into exactly how, and we all know why).

Some receivers are cast rather than milled from a forged billet.

There are only a couple suppliers of (blank) receivers out there and all of the major makers use them.
DevilPig  [Team Member]
3/5/2011 10:00:49 AM
Originally Posted By Adirondack1:
Mil-spec in what regards?
Materials?
Surface finish?
Obviously the interior dimensions are different (I won't go into exactly how, and we all know why).

Some receivers are cast rather than milled from a forged billet.

There are only a couple suppliers of (blank) receivers out there and all of the major makers use them.


I think the OP is just confused because he saw the two types of buffer tubes and extrapolated that to thinking that all AR parts are either commercial or milspec...

I could be wrong though
eltice  [Member]
3/5/2011 10:03:13 AM
More so with regards to dimensions.

My concern, and as someone pointed out, is that if I buy a mil-spec buffer tube, it won't fit in a commercial receiver, or vice-versa. Maybe it doesn't matter as long as the tube and butt stock match.

Originally Posted By Adirondack1:
Mil-spec in what regards?
Materials?
Surface finish?
Obviously the interior dimensions are different (I won't go into exactly how, and we all know why).

Some receivers are cast rather than milled from a forged billet.

There are only a couple suppliers of (blank) receivers out there and all of the major makers use them.


eltice  [Member]
3/5/2011 10:05:03 AM
This is exactly why I am wondering the differences.

Originally Posted By DevilPig:
Originally Posted By Adirondack1:
Mil-spec in what regards?
Materials?
Surface finish?
Obviously the interior dimensions are different (I won't go into exactly how, and we all know why).

Some receivers are cast rather than milled from a forged billet.

There are only a couple suppliers of (blank) receivers out there and all of the major makers use them.


I think the OP is just confused because he saw the two types of buffer tubes and extrapolated that to thinking that all AR parts are either commercial or milspec...

I could be wrong though


DevilPig  [Team Member]
3/5/2011 10:07:24 AM
Originally Posted By eltice:
This is exactly why I am wondering the differences.

Originally Posted By DevilPig:
Originally Posted By Adirondack1:
Mil-spec in what regards?
Materials?
Surface finish?
Obviously the interior dimensions are different (I won't go into exactly how, and we all know why).

Some receivers are cast rather than milled from a forged billet.

There are only a couple suppliers of (blank) receivers out there and all of the major makers use them.


I think the OP is just confused because he saw the two types of buffer tubes and extrapolated that to thinking that all AR parts are either commercial or milspec...

I could be wrong though




Well, like I said before the only parts (for the most part) on a basic AR that won't interchange are stocks and buffer tubes that aren't alike (ie: milspec with milspec and commercial with commercial). But either buffer tube will fit any receiver.
KBAD  [Team Member]
3/5/2011 10:09:02 AM

Originally Posted By eltice:
More so with regards to dimensions.

My concern, and as someone pointed out, is that if I buy a mil-spec buffer tube, it won't fit in a commercial receiver, or vice-versa. Maybe it doesn't matter as long as the tube and butt stock match.

Originally Posted By Adirondack1:
Mil-spec in what regards?
Materials?
Surface finish?
Obviously the interior dimensions are different (I won't go into exactly how, and we all know why).

Some receivers are cast rather than milled from a forged billet.

There are only a couple suppliers of (blank) receivers out there and all of the major makers use them.


You're thinking is correct. It just matters that the stock and tube are both either milspec or comm. A milspec or comm buffer tube will work with any lower...just make sure you get a stock matches the buffer tube.

niteghost  [Team Member]
3/5/2011 10:12:58 AM
If your talking dimensionally, I believe the only thing that you should be concerned about is the buffer tube. The diameter of a mill spec and commercial spec buffer tube is different. If you get a mil spec buffer tube you need a stock that will fit it and vise verse. I am sure that dimensions and tolerances differ from manufacture to manufacturer and mill spec can be referring to several different things like the materials used, manufacturing process, tolerances ect. My general rule of thumb is this, I don't mix match uppers, lowers and LPK's. If I buy a RRA lower then I use a RRA upper and LPK. A lot of people will say there no need in that and I would agree with them, that's just my way of assuring that I end up with a good finished product.
DVCAPI  [Team Member]
3/5/2011 1:19:30 PM

Originally Posted By niteghost:
If your talking dimensionally, I believe the only thing that you should be concerned about is the buffer tube. The diameter of a mill spec and commercial spec buffer tube is different. If you get a mil spec buffer tube you need a stock that will fit it and vise verse. I am sure that dimensions and tolerances differ from manufacture to manufacturer and mill spec can be referring to several different things like the materials used, manufacturing process, tolerances ect. My general rule of thumb is this, I don't mix match uppers, lowers and LPK's. If I buy a RRA lower then I use a RRA upper and LPK. A lot of people will say there no need in that and I would agree with them, that's just my way of assuring that I end up with a good finished product.

The main difference in LPK's is the quality of the roll pins. As to upper/lowers a 'Billet' upper looks better matched to a 'Billet' lower. Other than that it's just the finish and whether it matches the other part. You can take 100 lowers from any manufacturer and find some will be closer to spec than others, not every slug gets stamped like every other slug. The real problem comes when the tolerances start to stack up.
HS2  [Team Member]
3/5/2011 3:24:26 PM
OP,

Milspec and commercial buffer tubes will both work on any lower receiver since the threads are the same. Personally, I'd recommend a mil-spec tube.

As to the lower receiver... they are all made to the same basic spec, so there is no 'commercial' lower. They are all interchangeable, although there are certainly differences in overall fit and finish.
eltice  [Member]
3/5/2011 5:55:39 PM
Thanks everyone for the input. You guys have helped clear things up a bit.....at least until I start trying to put the lower together. :)
niteghost  [Team Member]
3/5/2011 7:55:51 PM
Originally Posted By eltice:
Thanks everyone for the input. You guys have helped clear things up a bit.....at least until I start trying to put the lower together. :)


Here is a great "how to" guide to help you put your lower together.

altopwescap  [Member]
3/5/2011 10:12:33 PM
A true Mil Spec AR lower is marked M-16 has a shelf and extra pin hole for the automatic sear. As far as the threaded hole for the extension/ buffer tube, they are all one standard or mil spec thread size. As for the lowers the rear area of the cutout at the selector hole can take several configurations. High shelf, low shelf, Dias ready, semi only (Colt variants that are not cut out at the selector hole) to name a few.
warpig8654  [Team Member]
3/6/2011 2:22:11 PM
Originally Posted By altopwescap:
A true Mil Spec AR lower is marked M-16 Property of US Gov't has a shelf and extra pin hole for the automatic sear. As far as the threaded hole for the extension/ buffer tube, they are all one standard or mil spec thread size. As for the lowers the rear area of the cutout at the selector hole can take several configurations. High shelf, low shelf, Dias ready, semi only (Colt variants that are not cut out at the selector hole) to name a few.


Parrandero  [Member]
3/8/2011 10:00:09 PM
Originally Posted By Adirondack1:
Mil-spec in what regards?
Materials?
Surface finish?
Obviously the interior dimensions are different (I won't go into exactly how, and we all know why).

Some receivers are cast rather than milled from a forged billet.

There are only a couple suppliers of (blank) receivers out there and all of the major makers use them.


Who makes a cast receiver these days?
Effenpig  [Team Member]
3/8/2011 10:04:33 PM
I know DPMS does. Not sure who else though

ETA: nevermind, I misread the catalog. They offer milled from billet and forged lowers

Don't forged lowers start with a cast though?
warpig8654  [Team Member]
3/8/2011 10:18:15 PM
Originally Posted By Effenpig:
Don't forged lowers start with a cast though?


Forged receivers start as a raw forging.
458winmag  [Team Member]
3/8/2011 10:22:06 PM
Originally Posted By Effenpig:
I know DPMS does. Not sure who else though

ETA: nevermind, I misread the catalog. They offer milled from billet and forged lowers

Don't forged lowers start with a cast though?


No,
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