AR15.Com Archives
 What "type" of buffer tube do I have?
skunk-ape  [Team Member]
3/3/2010 6:42:09 PM EST
I am looking at a Magpul CRT stock
I have a S&W M&P 15 and I have left the stock alone.

If I understand right this stock from Magpul



should go right onto my buffer tube.

but here is the question on the site I don't understand how to answer


This Magpul CTR mounts on Military Specification AR15/M16 carbine receiver buffer tube (including Colt, CMT, LMT, Vltor, Stag and similar manufacturers). It does not include buffer tube, buffer, or butt pad. The stock uses a standard sized pin to lock into the holes of your existing buffer tube. While the pin is the same size as the standard CAR stock it is supported on the sides 4x as much as the standard CAR latch.

Note: There are two types of buffer tubes (receiver extensions) in common use: Mil-Spec and Commercial. If you have a Commercial buffer tube on your rifle, make sure you order the Commercial CTR.


I hope one of you know this..


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JSharp  [Team Member]
3/3/2010 6:53:15 PM EST
The diameter of the mil-spec buffer tube is 1.14"
The diameter of a commercial buffer tube diameter is 1.17"
shiky  [Team Member]
3/3/2010 6:58:40 PM EST
i THINK the M&P uses a commercial tube, but i'm not sure
joesrcool  [Member]
3/3/2010 7:03:07 PM EST
Mil-spec, positive
UGA02  [Member]
3/3/2010 7:03:13 PM EST
14point5  [Team Member]
3/3/2010 7:14:47 PM EST
If you have a factory built S&W M&P-15 rifle that you have not tampered with, it has a mil-spec stock.

If you bought it second hand, measure it...
paradox87  [Member]
3/3/2010 8:43:21 PM EST
Originally Posted By 14point5:
If you have a factory built S&R M&P-15 rifle that you have not tampered with, it has a mil-spec stock.

If you bought it second hand, measure it...


Correct, my M&P15 has a mil-spec tube.
shrikefan  [Team Member]
3/3/2010 10:17:53 PM EST
Hint: a lot of times a mil spec stock will go on a commercial buffer and be a nice snug fit.
CWDraco  [Member]
3/4/2010 1:06:25 AM EST

Originally Posted By shrikefan:
Hint: a lot of times a mil spec stock will go on a commercial buffer and be a nice snug fit.


Hint: Wrong. Most times when a person tries to install a Mil-spec stock on a Commercial tube the stock gets stuck in one spot and requires a hammer to move it. There are times when a poorly made mil-spec stock is slightly wider, and / or a poorly made commercial tube is slightly thinner, and those two make a tight fit..but that is rare. When dealing with a Mil-spec Magpul, you best hope that Commercial tube was made smaller or you will be the proud owner of a fixed stock.

Also Magpuls diagram is old. Manufactures have now changed how they make tubes.

Things to look for now when you can not measure it.
1) Look at the picture of the mil-spec. Notice the wide threading behind the tubes threads. This is a good sign of a Mil-spec stock.

2) Run your finger over the threads and tube. If the threads are even with the tubes body, its a Commercial, if the threads are raised its a Mil-spec.

Commercial tubes are made the same diameter as the receiver and the threads are cut into it.
Mil=spec sized tubes are smaller and the threads need to be rolled, meaning the metal is crushed / shaped into threads,
This is why / how both threads are nearly the same, but the tubes are completely different diameters.

There are a lot of commercials with straight backs and there are Mil-specs with lower lips and threading that stops dead (no wide lead threads).
skunk-ape  [Team Member]
3/4/2010 3:52:35 AM EST

Originally Posted By paradox87:
Originally Posted By 14point5:
If you have a factory built S&R M&P-15 rifle that you have not tampered with, it has a mil-spec stock.

If you bought it second hand, measure it...


Correct, my M&P15 has a mil-spec tube.

thanks to all of you!
yep, it looks like my stock M&P is the mil-spec for sure.


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