Why is there a difference between commercial and mil-spec buffer tubes?

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kiltmonkey

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A few months ago I bought a PWS AR from Questar and I found out its buffer tube is mil-spec. This meant that I can't use the commercial Magpul CTR stock I already have.

I know that there's a difference with the width and the ends between the commercial and mil-spec buffer tubes. My question is why is there a difference? Why isn't there just one type of AR buffer tube?
 
Bingo,

Manuf costs......

For the most part they are the same dang thing.... cept one says "mil-spec" and costs four times as much.... and not cross compatible.

Someone on here resently had a nice blurb talking about the manufacturing process between the two tube and could clearly explain why it is cheap to manuf a comm tube over a mil tube. (Not that that helps very much)
 
The mil-spec tubes generally have turned threads that are 'full-form' as opposed to commercial tubes that generally have roll-formed threads that are 'topped'.
The mil-spec tube uses a special cutter to shape the 'body' whereas the commercial is as forged/extruded. (*note* extruding is a form of forging although usually forging refers to stamped between two dies )

There is a rumor (possibly a myth) that at some point there were commercial tubes made with the buffer hole extruded and an end cap welded on the end, although I have never ever seen an example or any evidence of this. If it were true, it would be glaringly obvious as when you anodize welded aluminum, the weld sticks out like a sore thumb as the colour is different.

As such, the difference in strength between a mil-spec and a commercial is marginal at best and if you were to ever break either one, you're using your gun wrong ;)

Short answer - commercial is cheaper to make.
 
Tubes can be made several different ways.
I've seen extrusions that where threaded and spot welded on the ends for commercial tubes.

Materials are also an issue. I've no idea why in this day and age people don't use MilSpec tubes.
 
I've seen extrusions that where threaded and spot welded on the ends for commercial tubes.
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Do you know who (company) made them and how long ago? If you say you've seen it, I'm inclined to believe you but I've never seen such an animal.

I've no idea why in this day and age people don't use MilSpec tubes.
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Because they are more expensive and most commercial guns come with commercial tubes ;)
 
The only reason commercial tubes were made was to lower manufacturing costs.

A milspec tube is made to a larger diameter to begin with, the threads are then cut (I believe some are rolled also) and the rest of the tube is planed down with a special tool. You can usually see lines running down the tube from this.

Commercial tubes are not planed down. They are made slightly larger final diameter so that the threads can be rolled into them as is.

Thus, although they are booth threaded the same, milspec tubes have thicker/deeper threads.
 
Thus, although they are booth threaded the same, milspec tubes have thicker/deeper threads.
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Then you dont understand how a thread specification works. If milspec and commercial threads were different one of those specs would not screw into the lower. The threads MUST be within a few thou of each other in order to be compatible.

A thicker or deeper thread is not the same and would result in two parts that would either not screw together or would be excessively sloppy. If milspec threads are really thicker and deeper then that would represent an inferior thread fit and we should all be clamoring for commercial spec parts.

Having cut many hundreds of threaded parts manually I can tell you that a difference of a couple of thousandths of an inch can be the difference between being able to screw parts together or not.

A difference of .002" will make no practical difference in the strength of that thread system.
 
Somewhat related question:

If I run into the problem of buying a gun (NEA) with a "commercial tube", but want to use a mil-spec stock on it, can I just change the tube out and re-install all of the other existing parts (buffer, spring, etc) inside of the new "mil-spec" tube?
 
Suputin said:
Then you dont understand how a thread specification works.....
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I guess I should of said the threads are higher… I would have thought you would have known that… here is a picture to illustrate, booth tubes screw in to any receiver, but look the dimensions on the threaded ends are different… you can also see on the milspec tube the threads appear to stick out and on the commercial tube they appear to be even with the rest of the tube…

Buffertube_Specs.jpg
 
The commercial tubes are bigger so it's quite normal that the threads are lower, how else are they going to fit into a lower receiver?
 
Mr. Spectacular said:
Somewhat related question:

If I run into the problem of buying a gun (NEA) with a "commercial tube", but want to use a mil-spec stock on it, can I just change the tube out and re-install all of the other existing parts (buffer, spring, etc) inside of the new "mil-spec" tube?
Click to expand...

Yes
 
If you cut threads into a tube you weaken it. Milspec starts with a thicker threaded tube, and cuts off the excess weight from the unthreaded portion. Commerical spec starts with a larger diameter tube and just threads its. Less machining, but you wind up with different dimensions for the whole unit.
 
lol, what's not to feel safe about?? If you break either you're doing something wrong with your rifle. It's an aluminum tube, not a jack handle ;)
 
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