What kind of rifle is it? If you go to Magpul's website you can print out a diagram that you can use to measure your buffer tube.

I'm willing to bet you've got the commercial buffer tube but you still want to measure it.

 

You need good calipers to measure. However, there are visual clues. The Mil-Spec tube is downsized from the tops of the thread screws. The rear most threads of the Mil-Spec tube will be slightly truncated. A Mil-Spec tube will be square in the back end. A Commercial tube will be the same diameter at the tops of the threads and along the tube and will usually have a slight 5 degree angle at the back end. If you put a Mil-Spec slider on a Commercial tube it can jam or cause damage. If you put a Commercial slider on a Mil-Spec tube, it will be even more loose than normal. That is why they must match.

 

You don't necessarily need calipers, but they do help.

All you need to do is measure the outside diameter of the buffer tube across the width of the tube. Commerical tubes are 1.170 and mil-spec tubes are only 1.140. Surprisingly, three-hundredth of an inch make a world of difference in the stock fit!!

Good luck...

 

http://www.magpul.com/pdfs/technotes/ctr/buffertubeid.pdf

 

What brand rifle do you have?


Or you could always refer to "THE CHART!!!"

 

does any body have a pit that compares side by side. ive seen it but i cant find it.

 

ok i used the calipers i have and got 1.169 so thats close enought to be a commercial tube.

is there any benifit of one over the other?

 

ok i used the calipers i have and got 1.169 so thats close enought to be a commercial tube.

is there any benifit of one over the other?

Benefit of milspec tube is that you'll have more options as far as stocks go...

 

measure it.

 

does any body have a pit that compares side by side. ive seen it but i cant find it.

ask and ye shall receive.......mil-spec on right

benefits of the mil-spec tube are strength, and more choices of the kewl stocks.

 

why on earth did someone decide we needed two different tubes? it does seem like it would be slightly cheaper to machine the commercial tube and im sure that is why. but for such a modular rifle it seems retarded to add a part that makes it less modular.

 

why on earth did someone decide we needed two different tubes? it does seem like it would be slightly cheaper to machine the commercial tube and im sure that is why. but for such a modular rifle it seems retarded to add a part that makes it less modular.

Some manufacturers will do anything to save a buck, and the un-educated AR buyer only discovers these things after his purchase.
The commercial sized extension is just one of the ways.

 

Some manufacturers will do anything to save a buck, and the un-educated AR buyer only discovers these things after his purchase.
The commercial sized extension is just one of the ways.

well at least the stock i want comes in a commercial one also.

 

but to me the commercial tube makes more sense. its easier to manufacture and has got to be cheaper or else they wouldn't have ever made them. and there doesn't seem to be any benefit to the mil-spec besides stock choice.
i guess the commercial could be a tad heavier due to it being larger in diameter but i doubt its that much of a difference

 

Yes, there is a difference, other than cosmetics.

from a FAQ on arfcom

Q: What is the difference between the Mil-Spec and the Commercial Receiver Extensions ('buffer tube')? Who uses what?
A: The commercial tubes are slightly larger in diameter where the stock slides, but slightly smaller in diameter when it screws into the receiver. Either can be installed on standard lowers, with the Mil-Spec one actually having the stronger interface (more surface area of the threads engage the receiver).

Mil-Spec ( 1.148" outer diameter): Colt, LMT, CMT (Stag, S&W, CMMG), VLTOR
Commercial (1.168" outer diameter): Everyone Else (Bushmaster, RRA, DPMS, Olympic, etc.)

Think about it for a sec, why would the military add a machining step if not necessary for the best result?

 

Yes, there is a difference, other than cosmetics.

from a FAQ on arfcom



Think about it for a sec, why would the military add a machining step if not necessary for the best result?

very good point but it is ran by the government and lets just say they aren't the best at streamlining things but the military probably is better then the other branches of the gov. but it still makes me wonder

can someone measure the outside of the threads on a mil spec tube for me? just curious in the actual difference in measurements.

 

There are quite a few differences between Milspec & Commercial Buffer Tubes.

• Mil Spec
• 7075T-6 forged aluminum
• 7.25" Long
• 1.14" OD
• .073" Outer wall thickness
• Squared End

• Commercial
• 6061T-6 extruded aluminum
• 7.8" Long
• 1.17" OD
• .085" Outer wall thickness
• Tapered End

 

Haha, Looking at getting a Magpul CTR for a current build project. Trying to find out which one I should get. BOSS has been very helpful. But I google milspec buffer tube and lo and behold what shows up!!! XDTALK!!

Current build can get whatever I want. But I'm also buying a M&P15T very soon. I can't find out if that has a mil-spec or a Commercial. From someone's post on here it has a commercial. Is that true? How hard is it to replace it....

 

buying a M&P15T very soon. I can't find out if that has a mil-spec or a Commercial.

s&w uses milspec size

 

I'm also buying a M&P15T very soon. I can't find out if that has a mil-spec or a Commercial. From someone's post on here it has a commercial. Is that true? How hard is it to replace it....

its not hard at all. just get a stock wrench and maybe a torch to heat it up.

turn the castle nut counterclockwise until it breaks loose. (heating it up a bit helps just don't over do it) carefully rotate the castle nut until you can remove lift the plate under it up so the rear take down detent spring doesn't go flying.

after you have the castle nut backed off and the plate lifted back put your thumb on the buffer spring Detent (there is s spring uder it as well and it will go flying if you don't hold it down) then twist the receiver tube off

take the plate and castle nut off the old receiver put it on the new receiver thread the new receiver tube on to the lower once it reached the point of the buffer spring detent push it down and thread it over it. until the the tube and plate are lined up then tighen everything up. and either locktight or stake the castle nut

but the M&P should have a Mil Spec tube.