I've been sucked into the world of Telestocks. buffers, crane stocks, etc.  The 2005 SEBR is a Bushmaster M4-style Carbine and I've been getting mixed answers as to the type of TUBE they use.

Anyone have pix of Mil-Spec vs. Non Mil-Spec?

What's the deal with Mil-Spec buffer tubes and Mfg. that DON'T use them?

The non-milspec versions are cheaper to make.  If you have a SEBR, its the cheaper version.

AFAIK Bushmaster does NOT use a mil-spec buffer tube.

Colt, LMT and Stag use Mil-spec buffer tubes.

The SOPMOD stock will only fit a mil-spec tube.

HS1's tube isn't mil-spec

It drives me nuts that the knock off companies started making non spec buffer tubes!

Funny how people will bash COLT for not using mil spec pin diameters, meanwhile they run around with all kinds of other non spec junk on their Bushmasters. hacko.gif

It goes kinda like this here...(at least the way I take it.)

Milspec tubes are slightly smaller in diameter because the blank is threaded and then milled to the correct diameter, making the entire tube slightly smaller than the threading itself.

Non milspec tubes simply have the threading cut into the tube, keeping the tube the same diameter as the threads.

Non-milspec stocks will generally fit on milspec tubes, but will be very sloppy.  Milspec stocks will not fit onto non milspec tubes.  (Although, I did catch a thread somewhere that someone used a screwdriver handle and various grits of sandpaper to "mill out" the hollow on a milspec stock to make a very snug fit on a non milspec buffer tube.)  As usual, YMMV.

Quoted: It drives me nuts that the knock off companies started making non spec buffer tubes! Funny how people will bash COLT for not using mil spec pin diameters, meanwhile they run around with all kinds of other non spec junk on their Bushmasters.

Interesting, but the flaw is that a Bushmaster owner can drop a different stock onto their spec receiver, while a Colt owner has a difficult time dropping in "spec" FCG parts to theirs.

Quoted: It goes kinda like this here...(at least the way I take it.) Milspec tubes are slightly smaller in diameter because the blank is threaded and then milled to the correct diameter, making the entire tube slightly smaller than the threading itself. Non milspec tubes simply have the threading cut into the tube, keeping the tube the same diameter as the threads. Non-milspec stocks will generally fit on milspec tubes, but will be very sloppy.  Milspec stocks will not fit onto non milspec tubes.  (Although, I did catch a thread somewhere that someone used a screwdriver handle and various grits of sandpaper to "mill out" the hollow on a milspec stock to make a very snug fit on a non milspec buffer tube.)  As usual, YMMV.

So although the outside is Wider/Fatter the inside of the tube should remain the same?  Which means I can install any form of BUFFER/SPRING combination and not run into any problems.  The problem will be when I try to shove a LMT SOPMOD Crane stock onto that wider non spec tube.

Dang cheap AR makers.  I can see why threading a tuber after the fact is WAY easier but a Military weapon needs to be as Mil-Spec as possible.

Now I need to learn up on FSB and A2 vs F-Marked and why Parkerizing under that is so important.

Is it a cost-saving measure? Yes. Is it such an annoyance? I say not, since you have some very good options.

There's plenty of very strong and inexpensive aftermarket telestocks that use the commercial tubes. I would say that the Cavarms M4 stocks, which use the commercial pattern tubes, are probably the best examples of M4 stocks on the market, milspec tube or not.

The only time when it'd be a pain is upgrading to a Crane/VLTOR/other exotic stock, where a new milspec tube will cost you all of  $30. Compare that to the costs associated with (for example..) having colt-spec firecontrol or takedown pin.

Though in this age of Stag/CMT stocks, my next build will have a milspec tube. But in the meantime, it's not such a big deal.

Quoted: It goes kinda like this here...(at least the way I take it.) Milspec tubes are slightly smaller in diameter because the blank is threaded and then milled lathe turned to the correct diameter, making the entire tube slightly smaller than the threading itself. Non milspec tubes simply have the threading cut into the tube, keeping the tube the same diameter as the threads. Non-milspec stocks will generally fit on milspec tubes, but will be very sloppy.  Milspec stocks will not fit onto non milspec tubes.  (Although, I did catch a thread somewhere that someone used a screwdriver handle and various grits of sandpaper to "mill out" the hollow on a milspec stock to make a very snug fit on a non milspec buffer tube.)  As usual, YMMV.

There, now that's better.

Quoted: Colt, LMT and Stag use Mil-spec buffer tubes.

Add Vltor to that list as well.

F-marked FSB is good becuase it means it GOES with a flat-top upper.  Colt for example will have an F-Marked FSB.  Using an A2 FSB on a Flat-Top upper is cheap.  This is becuase the FSB will be ever so slightly lower than what it needs to be if you have an A2 carry handle on top?

All that sound about right?  Just drop me a +1 or something please.  

Quoted: Interesting, but the flaw is that a Bushmaster owner can drop a different stock onto their spec receiver, while a Colt owner has a difficult time dropping in "spec" FCG parts to theirs.

Ah!  But that was the upside!  At least until BUSHY started making large pin inerds!

You could ONLY have true COLT parts in your Colt!

Yep it is a pain in the ass.

I love my colt(s), and my RRA.
I hate the Deer on Stag lowers so I purchased a few RRA Lowers, LPK, and one RRA M4 style stock only to find out that they are Non-Spec......

I thought I was good to go with all RRA stuff, but they cut through Anodized Layers to make M4 feedramps and Use Non-spec tubes.......

I still like RRA I just wish I would have known before buying.

So all in a nutshell, If I decided that I wanted to replace my Colt M4 stock with an M4 stock other than a Colt stock what would be my choice. A stock that I would be able to reuse my buffer and spring?

I don't believe the problem is with the buffer and spring.  The ID is correct, it is the OD and the radius on the slide rail that is different.

As long as you use Carbine lenght spring and buffer in carbine tubes your good to go.  Same for Rifle.

Does this topic applky to carbines only, or are their similar differences between mil-spec and non-mil-spec rifle buffer tubes?  

Quoted: Quoted: It goes kinda like this here...(at least the way I take it.) Milspec tubes are slightly smaller in diameter because the blank is threaded and then milled lathe turned to the correct diameter, making the entire tube slightly smaller than the threading itself. Non milspec tubes simply have the threading cut into the tube, keeping the tube the same diameter as the threads. Non-milspec stocks will generally fit on milspec tubes, but will be very sloppy.  Milspec stocks will not fit onto non milspec tubes.  (Although, I did catch a thread somewhere that someone used a screwdriver handle and various grits of sandpaper to "mill out" the hollow on a milspec stock to make a very snug fit on a non milspec buffer tube.)  As usual, YMMV. There, now that's better.

better, but wrong... you can not turn the tube because the raised keyway that kkeps the stock from turning and has the lock pin holes in it would get in the way - big time.

After the tube are threaded and the forward section turned, they are cut with a shaper machine the "shaves" or "planes" the tube with a rounded cutter... the process takes three passes and you can see on LMT tubes where the cuts do not fully blend smooth leaving those two slghty raised ridges along the length of the tube at 11 and 2

Quoted: better, but wrong... you can not turn the tube because the raised keyway that kkeps the stock from turning and has the lock pin holes in it would get in the way - big time.

You don't say.

Quoted: Is it a cost-saving measure? Yes. Is it such an annoyance? I say not, since you have some very good options. There's plenty of very strong and inexpensive aftermarket telestocks that use the commercial tubes. I would say that the Cavarms M4 stocks, which use the commercial pattern tubes, are probably the best examples of M4 stocks on the market, milspec tube or not. The only time when it'd be a pain is upgrading to a Crane/VLTOR/other exotic stock, where a new milspec tube will cost you all of  $30. Compare that to the costs associated with (for example..) having colt-spec firecontrol or takedown pin. Though in this age of Stag/CMT stocks, my next build will have a milspec tube. But in the meantime, it's not such a big deal.

The real down side is that the aftermarket tubes are weaker, it seems odd, that the one with *more* material woudl be weaker, but in most cases they are... if you check the dimensions of the extrusion used to make the tubes, you will see that there is not enough material (in most suppliers) to get a full profile thread peak -- the little point top of the threads are mising.

Aftermarket tubes have a habit of the threads failing and pulling out od the receiver under heavy (albeit unusual and unintended) loads.

And somehow, the buffer-tube on my Olympic Arms is bigger than the other "normal" two

Quoted: And somehow, the buffer-tube on my Olympic Arms is bigger than the other "normal" two

There is no spec for aftermarket tubes, as above different sullies of the extrusion end up slightly different sizes...

SO question, why in the heck isn't the mil-spec, the originally designed version, the easier one?  Why was it designed the way it was?

Quoted: Quoted: And somehow, the buffer-tube on my Olympic Arms is bigger than the other "normal" two There is no spec for aftermarket tubes, as above different sullies of the extrusion end up slightly different sizes...

Different enough to have to beat a Cav Arms and Bushmaster slider off with a hammer?




ETA: I never actually took the hammer to the Bushy slider, but I could tell by the way it started to go on I would've gotten the same result had I forced it.

Quoted: SO question, why in the heck isn't the mil-spec, the originally designed version, the easier one?  Why was it designed the way it was?

Because it's more expensive to make.

That said, I have 3 RRA 6 pos. stocks that I love.

WIZZO

Quoted: The real down side is that the aftermarket tubes are weaker, it seems odd, that the one with *more* material woudl be weaker, but in most cases they are... if you check the dimensions of the extrusion used to make the tubes, you will see that there is not enough material (in most suppliers) to get a full profile thread peak -- the little point top of the threads are mising. Aftermarket tubes have a habit of the threads failing and pulling out od the receiver under heavy (albeit unusual and unintended) loads.

Has this shown itself to be a problem? I haven't ever heard of a buffer tube of any make fail this way, but I do suppose it is possible. I would sooner expect the tube itself to tear before the threads would strip and disengage.

notice I said heavy, unintended, abuse... yes I have seen the break: falling from vehicles, being used as some sort of step for climbing, etc -- the average user need not worry about it.

Quoted: SO question, why in the heck isn't the mil-spec, the originally designed version, the easier one?  Why was it designed the way it was?

well... keep in mind to have an item in spec, you most likely have to make it that way, measure twice, cut once -- This is opinion only, but I would imagine as a designer that the intention was to be able to make all tubes, regardless of supplier, the same size, ensure that they are round and that the bore is concentric with the CL of the rifle.

Quoted: notice I said heavy, unintended, abuse... yes I have seen the break: falling from vehicles, being used as some sort of step for climbing, etc -- the average user need not worry about it.

So in these same situations, milspec tubes survived? Hmm, good to know.

I've yet to get my lower, and discussions like this have convinced me to go Mil-Spec as much as I can. I love "industrial strength" stuff. If Mil-Spec is stronger, I'm all for it.

GL

Quoted: Quoted: notice I said heavy, unintended, abuse... yes I have seen the break: falling from vehicles, being used as some sort of step for climbing, etc -- the average user need not worry about it. So in these same situations, milspec tubes survived? Hmm, good to know.

Well... I have seen milspec tube break too, but the ratio is far in favor of the aftermarket giving up the ghost. Keep in mind as Zakk talked about, these aftermarket tubes can run 0.0015 difference, this difference also determines what percentage of thread cut you are going to get...

Look at the thread of some after market tubes... some look good, others you will see have the tops of the thread peak missing (in some cases, as much as 50%), you will also see that some have threads that are inconsistant around the tube -- getting deep and shallow in the cut as they go around.

With a milspec tube, you are assured that the treads are cut to full profile and are consistant, that they are square to the CL and the buffer bore is inline with the rest of the rifle.

What about the wall thickness of the tube itself?

My milspec CMT tube from Eagle Firearms looks to have thicker tube walls than my bushmaster tube, which is exactly the opposite of what I was expecting!

It also has much better threads, and fits my Bushmaster receiver better than the factory tube did.

Quoted: What about the wall thickness of the tube itself? My milspec CMT tube from Eagle Firearms looks to have thicker tube walls than my bushmaster tube, which is exactly the opposite of what I was expecting! It also has much better threads, and fits my Bushmaster receiver better than the factory tube did.

I take that you are saying the milspec tube fits the receiver better? This is what I have been saying, the threads are a better engagement... as for the wall thickness, this is a bit of an illusion, the milspec appears thicker because the threads are cut full profile and that is what you are really looking at when you gaze into the open end...

Gunzilla - Yes I was trying to say that the CMT tube fit better. In fact MUCH better, with little or no slop. I understand what you are saying about how the complete threads would make the tube look thicker as well - that makes sense.

I am VERY impressed with the CMT product.

For me it was always price..well over $125 for a mil-spec telestock assembly..double if its a Colt.Now stag offers an assembly thats esentialy a CMT.Eaglefirearms in colorado has them..stag but we know stag+CMT..for $85 with a 9mm buffer and they are cheaper as you down grade the buffer.I know between both the inside legnth and diameter are the same.Colt machines the extensions from forgings while Bushmaster uses solid aluminum extrusions.Maybe the difference in size wich is minute has to do with how thw forgings and extrusions come already in the general diameter and shape.

Anyone ever actually the mic the thicknesses?

Quoted: Anyone ever actually the mic the thicknesses?

yes... but there is no need to really:
OD minus ID = X
X divided by 2 is wall thickness

Quoted: For me it was always price..well over $125 for a mil-spec telestock assembly..double if its a Colt.Now stag offers an assembly thats esentialy a CMT.Eaglefirearms in colorado has them..stag but we know stag+CMT..for $85 with a 9mm buffer and they are cheaper as you down grade the buffer.I know between both the inside legnth and diameter are the same.Colt machines the extensions from forgings while Bushmaster uses solid aluminum extrusions.Maybe the difference in size wich is minute has to do with how thw forgings and extrusions come already in the general diameter and shape.

Check out above for a description of how they are made... oh, one place where you can see a difference in who makes what the best is to take your rifle, hold it by the handguard straight out in front of you, muzzle up and drop it on a concrete floor a few times...

Quoted: Does this topic applky to carbines only, or are their similar differences between mil-spec and non-mil-spec rifle buffer tubes?

The "buffer tube" on rifles is part of the stock itself.

Quoted: Quoted: Does this topic applky to carbines only, or are their similar differences between mil-spec and non-mil-spec rifle buffer tubes?   The "buffer tube" on rifles is part of the stock itself.

Negative.

Quoted: Quoted: Does this topic applky to carbines only, or are their similar differences between mil-spec and non-mil-spec rifle buffer tubes?   The "buffer tube" on rifles is part of the stock itself.

No it isn't.

Though I am still looking for this 'Buffer Tube', all my ARs only seem to have Receiver Extensions....

I know one maker that uses extruded material to make buffer tubes. The material is considerably oversized and either turned or milled down, depending on whether it's a standard length or carbine buffer. Why do they use commercial specs? I have no idea.

After talking to my sources, It was explained to me that Colt sued the government for releasing the Technical Data package for the M4 out to bidders. Everyone was forced to return the Data package and threatened with legal action if they used any of the information relating to Colt's proprietary design changes.

This meant that nobody could manufacture Flattop parts to Flattop specs, except Colt.

This forced the aftermarket to stay with the origonal A2 specifications rather than the "F" height FSB and the Flattop carry handle, or just make up something out of the blue.

Apparently, later legal action may have changed that situation, but the commercial specs were already established.

I'll know more about the buffer tube later, someone with a history as far back as the origonal Armalites is being interrogated.

I'm just guessing, but the commercial diameter carbine buffer tube may have been another legal dodge to avoid a lawsuit from Colt.

Quoted: This forced the aftermarket to stay with the origonal A2 specifications rather than the "F" height FSB and the Flattop carry handle, or just make up something out of the blue.

Well I'll be a sonuva.  Good to know.  So this is why most detachable carry handles have the rear sight down a notch and why the FSB is slightly lower on an A2 over F-marked.  Does anyone know the tech specs as far as height difference on the FSB?

This thread got me thinking, so I got out a couple of stocks I had stashed away, a vernier caliper, and a Bushmaster carbine. I took a few photos and some quick measurements.

The aluminum stock on my carbine has always rattled. I recently read another thread about stopping the rattle, but I also remembered reading THIS thread. I compared the two extra carbine receiver extensions I had lying around, and I noticed that one of them has a noticeable step before the threaded portion. The main part is thicker, but it was apparently turned down to a smaller dimension to facilitate threading. This tube came with a Fiberite stock (bottom example in photo below).



The other 'extra' stock I had was another aluminum one (center example in above photo), not as nice in appearance as the one that came with my Bushmaster. This one has a tube that does not step down like the one that came with the Fiberite one. The receiver extension on my carbine is like this, as well. Like I said, I took a few measurements:

The one on the weapon has a diameter of 1.145"

The tube on the extra aluminum stock measures 1.152"

The stepped tube from the Fiberite stock is 1.180" where the stock slides, and is turned down to 1.152" at the threaded portion.

At this point I tried switching a couple pieces around. I removed the buttstocks from their respective tubes and attempted to swich them. The Fiberite stock went onto the straight tube just fine, but the aluminum stock didn't want to slide onto the stepped tube, and I wasn't about to force it. I put them back the way they originally came, taking note that the Fiberite stock had NO play or rattle, while the aluminum one had quite a bit of looseness to it, just like the one on the rifle.

Looking at the photo below, you can see a small gap where the tube slides into the aluminum stock, on the left, while the Fiberite stock on the right  fits tightly, with no rattle. You can also see the stepped tube on Fiberite stock:



Another thing I noticed was the dimension from the end of the slot to the rear of the receiver extension/buffer tube. It's obvious in the next photo:



The tube on the left is the one that came with the Fiberite stock. The slot ends approximately 0.330" from the end of the tube. The one on the right came with the aluminum stock. The dimension from the end of the slot to the end of the tube is greater by 0.110", or 0.440".

I had trouble with this one and I had to modify the aluminum stock to make it work properly because the tube actually protruded from the buttstock in the retracted position. That's just a bit off-topic here, and is a story for another time.

I just wanted to share my findings here. Hopefully we can determine exactly what a so-called 'milspec' carbine receiver extension really is. Anyone else have some photos that would help clarify this? Is my Fiberite stock milspec, or are both of these pieces considered non-spec?

(edited to correct photo references)

Quoted: I know one maker that uses extruded material to make buffer tubes. The material is considerably oversized and either turned or milled down, depending on whether it's a standard length or carbine buffer. Why do they use commercial specs? I have no idea. After talking to my sources, It was explained to me that Colt sued the government for releasing the Technical Data package for the M4 out to bidders. Everyone was forced to return the Data package and threatened with legal action if they used any of the information relating to Colt's proprietary design changes. This meant that nobody could manufacture Flattop parts to Flattop specs, except Colt. This forced the aftermarket to stay with the origonal A2 specifications rather than the "F" height FSB and the Flattop carry handle, or just make up something out of the blue. Apparently, later legal action may have changed that situation, but the commercial specs were already established. I'll know more about the buffer tube later, someone with a history as far back as the origonal Armalites is being interrogated. I'm just guessing, but the commercial diameter carbine buffer tube may have been another legal dodge to avoid a lawsuit from Colt.

The commercial, or aftermarket tube diameter came about as no more than ease of manufacture. When Jerry Drasen was making the first commercial knock-offs of the telescoping stock, he used a 1.170 extrusion to save manufacturing cost... this became the fe facto aftermarket standard, but there really is no commercial spec and they can range quite a bit... but it had nothing to do with legal issues at all, just cheaper to make.

The Mil-Spec is  1.150 +0/-0.005, it is achieved by cutting an extrusion down. The cutting is done with a shaped cutter that planes or shaves off material, this is done is three passes and you can get an idea of how it works by looking at an LMT tube; their cutter does not quite line up perfectly and leaves two slight "ridges" down the length of the tube at eleven and one o'clock. One thing to think about with these tubes is that the threads are 1.1875, the aftermarket extrusions do not have enough material to get a full thread and they are weak there... if you look at an aftermarket tube, you will see that the threads are not "full", the tops of the threads are flat where there was not enough material to make the full profile.

Choate decided to make up for this by using a 1.1875 extrusion, but still did not shape or cut the tube, so they have yet a third (oversized) tube for their stocks.

It seems this comes up about once a week... Oh and btw, you may want to check your source on the flat-top thing there

Gunzilla-

Excellent intel. Thanks! That explains a lot.

wp

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