View Full Version : Mil-Spec Buffer tube ?
I looked up the spec for the buffer tube, 1.147. I measured mine at 1.150. Used a Vernier Caliper. I would think this is Mil-Spec. Any thoughts?
http://m4carbine.net/showthread.php?t=101
First post in that thread - good info, aside from just the dimensions.
SilverBullet432
08-12-13, 20:48
commercial tubes have a slanted back and they measure 1.168, i think you're ok
There are always variances in the tubes, so 1.15 may be a little tight, but it is fine. Commercial tubes are usually 1.17 inches and slightly larger.
Thanks for the info and thought's.
commercial tubes have a slanted back and they measure 1.168, i think you're ok
That's not always true - there are many commercial tubes with flat backs, unfortunately, and I believe there even a couple oddball "milspec" diameter tubes with slanted backs.
K.L. Davis
08-13-13, 11:20
That's not always true - there are many commercial tubes with flat backs, unfortunately, and I believe there even a couple oddball "milspec" diameter tubes with slanted backs.
True Dat! The only thing you can 100% sure of with an angled back is that it will harder to stand on end.
Good point. I ran across one or two (I think it was Iraq) and I was never able to narrow down where they came from. I have yet to see anymore of them since.
That's not always true - there are many commercial tubes with flat backs, unfortunately, and I believe there even a couple oddball "milspec" diameter tubes with slanted backs.
SilverBullet432
08-13-13, 17:45
That's not always true - there are many commercial tubes with flat backs, unfortunately, and I believe there even a couple oddball "milspec" diameter tubes with slanted backs.
Hmm interesting! I guess everyone likes to do their own thing then?
sinlessorrow
08-13-13, 18:37
Easiest way to tell is the threads.
Mil spec threads will be raised above the RE which commercial threads are generally inset in the RE.
But know this not all RE's are equal. Alot of manuf. who claim milspec are not extruded 7075.
The Threads measure the same as the receiver tube.
sinlessorrow
08-13-13, 23:35
http://ar15.co.za/wp-content/uploads/2013/04/Mil-Spec-vs-Commercial-Buffer-Tubes.jpg
Thanks again for all the information. I checked the ends of the receiver tubes and they are flat(square),as in the photo from sinlessorrow. I noticed that in the photo it had 1.148 as mil-spec. other places say 1.147. Must be a little variance allowed.
sinlessorrow
08-14-13, 11:46
Thanks again for all the information. I checked the ends of the receiver tubes and they are flat(square),as in the photo from sinlessorrow. I noticed that in the photo it had 1.148 as mil-spec. other places say 1.147. Must be a little variance allowed.
Did you check the threads as well?
as said, threads are the best/easiest way to tell. Mil has threads pressed on. The commercial tubes have the threads cut into the metal.
as said, threads are the best/easiest way to tell. Mil has threads pressed on. The commercial tubes have the threads cut into the metal.
That is true for all real milspec tubes, but be careful...there are milspec diameter tubes on the market that have cut threads, and I would be willing to bet if you search hard enough you could find commercial diameter tubes with rolled threads.
That is true for all real milspec tubes, but be careful...there are milspec diameter tubes on the market that have cut threads, and I would be willing to bet if you search hard enough you could find commercial diameter tubes with rolled threads.
I'd be willing to bet no one rolls threads on to the receiver extension, mil-spec of otherwise. I suppose it's possible, the min pitch diameter of the threads is the same as the min tube diameter, but it's not cost effective or required.
I'd be willing to bet no one rolls threads on to the receiver extension, mil-spec of otherwise. I suppose it's possible, the min pitch diameter of the threads is the same as the min tube diameter, but it's not cost effective or required.
You might want to call up Colt and tell them they're doing it wrong.
sinslessorrow,
Yes I measured the threads(post# 11),they are the same as the tube. Also they look as though they are cut into the tube. I'm not a machinist though.
sinlessorrow
08-14-13, 15:06
sinslessorrow,
Yes I measured the threads(post# 11),they are the same as the tube. Also they look as though they are cut into the tube. I'm not a machinist though.
Then you have a commercial RE.
Thanks again for all the information. I checked the ends of the receiver tubes and they are flat(square),as in the photo from sinlessorrow. I noticed that in the photo it had 1.148 as mil-spec. other places say 1.147. Must be a little variance allowed.
Variances ? Correct. My Colt shop drawings indicate the mil-spec extension tube specification is 1.145 - 1.150 .... I imagine most consider 1.148 because it's the midpoint of the specification and takes into account manufacturing variances.
This, along with the variances in the stock bore diameter (which can "stack" with variances in tube diameter) is why some stocks are tighter or looser then others on a given tube.
P
I had to add true milspec uses a 70 series aluminum alloy not a 60 series alloy.FYI
I had to add true milspec uses a 70 series aluminum alloy not a 60 series alloy.FYI, Close to twice as strong.
I'd be willing to bet no one rolls threads on to the receiver extension, mil-spec of otherwise. I suppose it's possible, the min pitch diameter of the threads is the same as the min tube diameter, but it's not cost effective or required.
Median PD for a 2A fit is 1.1429"
Median PD for a 3A fit is 1.1450"
The Mil-spec tube is made the diameter it is for the purpose of rolling the threads during manufacture.
albatrossarmament
09-20-13, 07:02
That's not always true - there are many commercial tubes with flat backs, unfortunately, and I believe there even a couple oddball "milspec" diameter tubes with slanted backs.
Just as a note of reference. I did have 2 examples of mil-spec diameter tubes with "slant backs" in my possession at one time. The problem is, when using them with mil-spec M4 stocks (from BCM) the "slant back" tube would hang out of the rear of the stock about 1" when collapsed. If I remember correctly, they also wouldn't close completely on a VLTOR stock with the rubber buttpad.
The back story is, I bought two Armalite lowers from gunbroker. They were gunsmith builds using all Armalite parts. I got them cheaper then I could have built them myself. Upon receipt, I was pissed because I thought I had commercial tubes because they had "slant backs". Upon further inspection I found that they were mil-spec diameter. Called Armalite, and they said that there was a batch made for them that came in that way and they were quarantined. Armalite had no idea how I ended up with two of them. They immediately sent me out two correct tubes, and from there I was good to go.
Point being, weird variances exist as manufactures try to re-invent and "improve" on proven specs.
K.L. Davis
09-20-13, 19:21
I'd be willing to bet no one rolls threads on to the receiver extension, mil-spec of otherwise. I suppose it's possible, the min pitch diameter of the threads is the same as the min tube diameter, but it's not cost effective or required.
I have seen first hand, tens of thousands of milspec tubes made with rolled threads... and I know the shop I was in is not the only shop that rolls in threads.
K.L. Davis
09-21-13, 10:25
Old post... https://www.m4carbine.net/showpost.php?p=415&postcount=1
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