The Down Range Forum
Member Section => Tactical Rifle & Carbine => Topic started by: billt on January 01, 2012, 09:15:34 AM
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Is Colt the only manufacturer that uses Mil-Spec Buffer tubes? I ask because I'm thinking of going to the Vltor E-Mod Buttstock on my Bushmaster and Colt AR-15's. They came stock on my LWRC guns, and I really like the way they fit and feel. I don't want to replace the buffer tubes, springs, or Castle Nuts. I'm looking for a nice, easy off / on installation. No muss, no fuss, no cuss. I'm almost positive the Colts, (6920 & 6940 Monolith LEO Carbines), are Mil-Spec diameter tubes, and the Bushy's are Commercial diameter. I just wondered if there is a list of the different manufacturers, along with what size buffer tubes they use?
I was also thinking of going with one on my Rock River Arms LAR-9, 9 MM carbine, but I have no idea what they use on the 9 MM weapons, or if even Vltor makes one that would fit?? Also who has the best deals going on these things?
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Try the AR15 armory.com. They are friendly and helpful folks. The general AR thread will get you your answers.
FQ13
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I'd tell you to measure the end of the tube because Mag-Pul lists the differing sizes between the two on the website, but I can't tell the difference. The best bet is just to call Bushmaster up and ask.
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(http://i296.photobucket.com/albums/mm182/twyacht/Buffertube_Specs.jpg)
Amazon sells a gauge from Tactical Intent for like $1 or $2...
LMT, LWRC, Stag, M&P (Stag Clone), POF, Armalite, are all mil-spec lower receivers. DPMS, are commercial although they have done a great job confusing things now offering a mil-spec version..
I have heard Bushmaster's have both? ???
Not sure of Ruger, Olympic, and Para AR's,...quick call or google fu, may confirm, if someone doesn't already know (bafsu?)
The buffer, spring, and castle nut are all the same.
Put a caliper or real good tale of the tape, to check.
I have the VLTOR EMOD, mil specific, and it went on my mil-spec tube like a glove.
Good question,...and one that is important to avoid the wubble.... in picking a stock.
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I believe that Rock River uses commercial spec tubes on most of theirs.
A few more details on measurements from this magpul link:
http://cdn.magpul.com/downloads/Receiver_Extension_Comparison.pdf
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Thanks T.W. & Blackwolfe
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On my Bushmaster M-4 A-1, the Buffer Tube measures 1.165" about halfway out where the stock slides over it. But right in where it screws into the lower it measures 1.145". So I'm guessing I would need a Commercial Vltor E-Mod Stock, not a Mil-Spec?
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You are correct billt.
According to AR15.com,....Bushmaster is 99.9% Commercial tubed.
http://www.ar15.com/forums/t_3_12/442122_RE__Bushmaster_buffer_tube_mil_spec_or_commercial__.html
I also called my Black Rifle guy here at Guntech, Ft. Laud, and he confirmed standard Bushy tubes are indeed Commercial.
Don't forget a picture when you get the new stock... ;)
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Bill, I think Bravo Company might have somw specials on Vltor stocks right now.
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The easiest way to tell if your tube is commercial or mil-spec is to pull off your stock and look at the end of it. No need to measure diameter etc. If you look at the drawings that twyacht provided you can see that mil-spec tubes are flat/square on the end where commercial tubes have a slight angle. Also a commercial stock will fit on a mil-spec tube with a little slop but a mil-spec stock will never go on a commercial tube. Quite a few manufacturers use mil-spec besides Colt, Noveske, LMT, BCM and LaRue come to mind but I know there are others. The mil-spec tube is really a cheap upgrade since it's made from a much heavier gauge, thicker walled material than the commercial tubes. Thinner diameter and much thicker wall, lots more strength for $30-$40.
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If there is .015" difference at the thread diameter, (1.170 / 1.185), how can they both fit into the same lower?
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If there is .015" difference at the thread diameter, (1.170 / 1.185), how can they both fit into the same lower?
As far as I know the only difference is in the shaft diameter, not the threads. I only purchase Mil-Spec tubes for all my builds (at least 25 different brands of lowers) and I've removed commercial tubes and installed Mil-Spec tubes in their place many times as well.
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Diameter doesn't mean that much if you allow for varying percentages of thread contact.
To use a common thread for an example, according to the chart in the "Machineries Handbook"
(27th ed. pg 1737 )
A 1/4 - 20 thread Class 1a has a major diameter of 0.2489 with a .0011 allowance.
But a Class 3a has a major diameter of .2500 with .0 allowance
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A 64th on the diameter of a fine thread like that would make a big difference I would think. Unless that drawing is incorrect. I can see a difference in the tube diameter where the stock itself fits on, but not in the thread size. That's what I noticed when I miked the tube on my Bushy. It was smaller at the threads, larger further down the tube.
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What's made me always assume the thread is the same regardless is I've never seen a castle nut specified as Mil-Spec or commercial, they just sell castle nuts.
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First off, I'm not an AR guy and don't own one and have never seen the buffer tube on one.
This is from the AR something or other...
The biggest differences between the two tube types are: 1) The buffer tube diameter itself 2) The diameter of the threads in relation to the diameter of the tube.
Mil-Spec: On the mil-spec buffer tube… the threads at the front are actually a larger diameter than the rest of the tube itself. In manufacturing, a large tube is used and threads lathed as normal. Next, the rest of the tube must be milled down to the military specified diameter. I’m guessing this step requires more work / precision… and costs more.
Commercial-Spec: In manufacturing, you begin with a tube that matches the final tube diameter. The threads are cut into the front end with a lathe just like any other threaded pipe. I imagine this to be just like the copper water pipe used in my house.
Tubing is measured by it's ID which is constant (to a point) and can have a tolerance OD of "x" depending on size and the wall thickness can have a tolerance of "y"!. These two variables can effect the strength of the tubing involved. From what I can tell, the threaded portion is common to both diameters which explains why there is only one castle nut available.
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To me the Commercial sized tube just makes more sense based on that. I've never heard of anyone breaking either.
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Are there two different buffers and springs available or are they interchangeable?
Just curious as it would seem that the ID is more critical than the OD for operation. The OD of the buffer tube would effect different stocks that would fit I'd expect. The other thing I can see is that the Mil-Spec tube has a slanted ass end to it to more closely match the shoulder angle of a stock.
Correct me if I'm off here...
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You would think someone would manufacture a sleeve of some type that would make up the difference between the 2. They sure seem to have issues standardizing the simplest of things with these rifles.
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Again, I don't know squat about these guns but my SIL just did an AR10 build starting with an Armalite lower. He bought a bunch of stuff only to find that none of it fit properly and after numerous returns and speaking with whomever he bought the lower from, he ended up having to buy nearly everything from Armalite to complete the build.
His cost to build was more than he would have paid for a stock Armalite with a flattop upper, less the bull barrel he used.
He was pretty pissed at that point.
Nice rifle but it's not a plinker by any means. Damn thing weighs nearly 15 pounds.
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Tim, First off, the buffer spring.
The difference in is between Rifle length, or carbine length, both the spring, and the buffer it's self are different.
(want to buy a rifle length buffer and spring ? )
Second, Armalite.
pretty much everything about Armalite is proprietary, Your SIL would have been much better off going with DPMS since their AR internals are pretty much one size fits all, less expensive, and have a much better chance of being compatible with other "AR" after market products.
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Second, Armalite.
pretty much everything about Armalite is proprietary, Your SIL would have been much better off going with DPMS since their AR internals are pretty much one size fits all, less expensive, and have a much better chance of being compatible with other "AR" after market products.
Well, he knows that now but after dropping 1600 bucks on a build, he's gonna be hard pressed to get his money back!
This is kind of typical for him though. He's always looked at the end before he realizes where he should begin and generally he's making the wrong choices. Thankfully, he's my daughters problem, not mine!
BTW, I call him my SIL but they're not married...
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Are there two different buffers and springs available or are they interchangeable?
Just curious as it would seem that the ID is more critical than the OD for operation. The OD of the buffer tube would effect different stocks that would fit I'd expect. The other thing I can see is that the Mil-Spec tube has a slanted ass end to it to more closely match the shoulder angle of a stock.
Correct me if I'm off here...
The buffers and springs are standard as well. I have seen buffer tubes folded in half before and do know that the mil-spec are much stronger with a thicker wall even though they are slightly smaller in O.D. If you have a commercial tube and you just use your rifle for recreation etc. then it's probably never going to be an issue unless you want some higher end stock that is only made in a mil-spec version like a sopmod or some of the vltor models. I don't see why you'd ever do a build with a commercial tube when the price really isn't that much different. For as much as some accessories and parts cost I wouldn't think twice about spending an extra $15 or so upfront. If I ever end up with a rifle I plan to keep thats the first thing I do as well. I like all my stuff to be uniform and I usually have a stock or 3 laying around in a parts box so I want all my stuff the same. I think just as important as the tube though is that the castle nut is properly staked. If you have a commercial tube and an unstaked castle nut now is the time to change it and properly install a mil-spec tube.
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Again, I don't know squat about these guns but my SIL just did an AR10 build starting with an Armalite lower. He bought a bunch of stuff only to find that none of it fit properly and after numerous returns and speaking with whomever he bought the lower from, he ended up having to buy nearly everything from Armalite to complete the build.
His cost to build was more than he would have paid for a stock Armalite with a flattop upper, less the bull barrel he used.
He was pretty pissed at that point.
Nice rifle but it's not a plinker by any means. Damn thing weighs nearly 15 pounds.
AR-10's are an entirely different animal, 2 distinct types with almost nothing interchangeable between the 2. There are other manufacturers that use the Armalite pattern, I think Knight's/Stoner and LaRue if I remember correctly and the other style is the DPMS/CMMG and others. You can tell by the way the receiver is shaped at the rear but I don't mess with either platform.
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All of the above mentioned is why I don't want to change the buffer tube. I just want a simple slide off / slide on installation. Otherwise your looking at opening up a Pandora's Box of problems. Stuck Castle Nuts, tubes and springs that either don't match, or else won't run correctly, etc. I just want to replace the stock, nothing else. If it ain't broke, I don't want it "fixed".
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All of the above mentioned is why I don't want to change the buffer tube. I just want a simple slide off / slide on installation. Otherwise your looking at opening up a Pandora's Box of problems. Stuck Castle Nuts, tubes and springs that either don't match, or else won't run correctly, etc. I just want to replace the stock, nothing else. If it ain't broke, I don't want it "fixed".
I guess you answered your own question then. As long as the stock you want is available in a commercial model then you're good to go. If the stock you wanted was a mil-spec only stock then you should buy the complete assembly so you have everything you need. You really don't have to worry about springs, buffers, castle nuts etc. though since they are all standard size with the only difference being rifle or carbine and the weight of the buffers.
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If you look at the Magpul reference, it shows that the commercial tube has truncated or flat threads and the milspec tube has threads that have a well formed peaks. I imagine that the commercial buffer tubes were developed, because they are probably cheaper to manufacture.
http://cdn.magpul.com/downloads/Receiver_Extension_Comparison.pdf