Bushmaster - Commercial or Mil-Spec Buffer Tube


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heavyshooter
November 16, 2011, 07:20 PM
I have a Bushmaster Model #XM15-E2S. How do I know if the buffer tube is Commercial or Mil-Spec. I am trying to determine which Magpul CTR stock to order.

Heavy

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crossrhodes
November 16, 2011, 08:14 PM
Measure it...nominal 1.150 for milspec and 1.170 for commercial.

hirundo82
November 16, 2011, 09:36 PM
As much as I hate linking to "The Chart (http://img.photobucket.com/albums/v408/gotm4/chart.jpg)," it occasionally comes in handy. Bushmaster uses commercial buffer tubes ("reciever extensions") on their rifles.

Z-Michigan
November 16, 2011, 11:30 PM
It will be commercial spec unless they changed something VERY recently.

madcratebuilder
November 17, 2011, 07:08 AM
I have a Bushmaster Model #XM15-E2S. How do I know if the buffer tube is Commercial or Mil-Spec. I am trying to determine which Magpul CTR stock to order.

Heavy
The Shrubs use a commercial RE, buy a mil-spec stock and replace the RE with mil-spec. Adding a H buffer would be good for a carbine gas system.

heavyshooter
November 17, 2011, 07:11 PM
What is the benefit of Mil-Spec over Commercial?

Onmilo
November 17, 2011, 08:00 PM
Some commercial tubes use a cheaper grade of aluminum and are extruded rather than forged.
Commercial tubes can be thin in the walls which means they are not as strong and can bend more easily. I found this out the hard way, bending a commerical tube so badly the rifle would not function after dropping the gun off a bench and onto a concrete pad.

I use Mil-Spec diameter tubes on all my collapsing stock rifles now and prefer VLTORs as my first choice. HTH

mastiffhound
November 17, 2011, 08:39 PM
I have a newer bushy, same model, made less than a year ago. What I have noticed:

MP marked barrel.
F marked front sight.
My sr556 has a commercial tube for sure, and my stocks with the bushy are not interchangable. The bushy stock is too small for the ruger sr556. I have tried because I was bored one day.
My gas key is propery staked.
Shrouded firing pin in the bcg.
Chrome lined barrel of course.

I can't remember all the mil-spec stuff but all of these things seem to be important to everyone else. I like my bushy because it shoots soft and is pretty accurate.
All this has made me think that Bushmaster has upped their quality. Has anyone else picked up a new one recently?

Matthew Courtney
November 18, 2011, 12:55 AM
Several companies, including Bushmaster, let QC slide when trying to keep up with the rush after the 2008 election. Most have gotten their QC issues straightened out.

My Bushmaster .308 ORC purchased in May of 2010 was made in March 2010 and has been completely checked out. It is exactly what it is supposed to be.

OP,

Measure the tube. Just because bushies leave the factory with commercial tubes doesn't mean that is what you have.

average_shooter
November 18, 2011, 01:00 AM
I have a newer bushy, same model, made less than a year ago. What I have noticed:

MP marked barrel.
F marked front sight.
My sr556 has a commercial tube for sure, and my stocks with the bushy are not interchangable. The bushy stock is too small for the ruger sr556. I have tried because I was bored one day.
My gas key is propery staked.
Shrouded firing pin in the bcg.
Chrome lined barrel of course.

Can't speak as to the buffer tube, haven't checked mine with calipers, but mine's got to be about six or seven years old now and has all the same properties as far as I can tell. I did swap out the gas block for a low profile railed block though. MP barrel, staked key, etc., all good to go. I've read that Bushmaster isn't up to spec, but mine has worked flawlessly save for choking on crappy reloads I made when first getting into .223 reloading that would have jammed up any rifle.

Edit:

Curiosity got the best of me, so I grabbed the calipers, my tube measures 1.170" OD.

But to me this...:
...nominal 1.150 for milspec and 1.170 for commercial.

... does not jive with this:
Commercial tubes can be thin in the walls which means they are not as strong and can bend more easily.

I would think the 1.170" tubes would therefore be thicker than the 1.150" tubes. Unless the internal diameter is machined out larger in the 1.170" tubes, but that doesn't make sense to me as I would think buffers and springs would be overly loose then.

Can anyone educate me on this?

DBR
November 18, 2011, 02:28 AM
The real differences between milspec and commercial receiver extensions are:

milspec:
"impact extruded" one piece 7075-T6 aluminum-meaning forged. 7075-T6 is about 60% stronger than the more common 6061-T6.
Rolled threads that have nearly full engagement with the receiver threads. Rolled threads are significantly stronger than cut threads.
Proper hard anodized finish with dry lube inside.

Commercial:
Usually extruded 6061-T6 alloy which is weaker than proper 7075-T6 alloy.
Cut threads that are weaker and only engage the receiver threads 60-70%
Unknown anodized finish.
Pressed on, swaged or welded end cap.
Usually no inside lube treatment.

Commercial tubes may be completely adequate for most civilian uses but they are not the same as real milspec parts for hard use.

Onmilo
November 18, 2011, 10:27 AM
Thinner side walls in a tube that externally measures 20 thousanths over the mil-spec tube will not cause any noticable degree of slop to the buffer or receiver spring.
20 thousanths is 14 microns greater than one half of a millimeter.(.020"=0.514mm)
A manufacturer can extrude a tube to any thickness & diameter desired or specified.
In the great big world half a millimeter it isn't much, but the thinner commercial tubes will bend or even collapse under a heavy stress load.

One of the reasons the cut threads on a commercial tube will only engage 60% of the receiver threads is because you can't cut deep threads on a thin tube.

1911crazy
November 24, 2011, 08:32 PM
this may be a stupid question but what part of the gun is the buffer tube
and how expensive is a mil-spec buffer tube

kwelz
November 24, 2011, 09:33 PM
The reciever extension/buffer tube is the part the stock attaches to.
Price is about the same.

DBR
November 25, 2011, 04:37 PM
A real milspec buffer tube would be a Colt "forged" part part. They cost about $60. A good quality mil sized part can be bought from Bravo Company. IIRC they are around $30.

Z-Michigan
November 25, 2011, 08:38 PM
A real milspec buffer tube would be a Colt "forged" part part. They cost about $60. A good quality mil sized part can be bought from Bravo Company. IIRC they are around $30.

I don't believe anyone including Colt is making a forged buffer tube, even though it's my understanding that forging is one of two methods compliant with the TDP (mil-spec). All the quality tubes I know of are made by the impact extrusion method, which is similar but not identical (and is quite different from the conventional continuous extrusion method used for most or all commercial-size tubes). The BCM, LMT, Daniel Defense, and Stag mil-spec (CMT) tubes are to my knowledge made by this method and are the correct size, as of course is the Colt. The quality of the BCM and LMT tubes is equal in all respects, and LMT adds a dry-lube film that can be a plus for smooth operation of the stock. The Spike's tube is the correct size and I expect it's made by an approved method but I don't know that for sure. The DSA mil-spec size tube is made out of 6061 aluminum and is not forged or impact extruded, but is instead basically a commercial style tube made to the mil-spec size, only. I could be wrong about any one of these as hardly anyone but a few industry types at another forum know anything about these details or talk about it, so my sources are limited.

DBR
November 25, 2011, 09:45 PM
Go here and look down the page:
http://www.specializedarmament.com/catalog/AR_15_Parts-4-0.html

You will see that there are two types of receiver extension offered: extruded and forged.

As I understand it "impact extruding" is a form of forging.

Look here: http://en.wikipedia.org/wiki/Impact_extrusion

And here: http://en.wikipedia.org/wiki/Forging

HavelockLEO
November 26, 2011, 12:26 AM
The last Bushmaster I had, about 2 years ago, had a commercial tube and I dont believe anythings changed in that time.

taliv
November 26, 2011, 12:51 AM
But to me this...:
...nominal 1.150 for milspec and 1.170 for commercial.

... does not jive with this:
Commercial tubes can be thin in the walls which means they are not as strong and can bend more easily.

I would think the 1.170" tubes would therefore be thicker than the 1.150" tubes. Unless the internal diameter is machined out larger in the 1.170" tubes, but that doesn't make sense to me as I would think buffers and springs would be overly loose then.

Can anyone educate me on this?

i believe you are correct. the reason the commercial tubes are larger diameter is because they are thicker, not thinner.

the ID on both types is the same.

1911crazy
November 29, 2011, 06:12 PM
The reciever extension/buffer tube is the part the stock attaches to.
Price is about the same.
the buffer tube attaches the forend to the upper receiver right ?

kwelz
November 29, 2011, 07:00 PM
the buffer tube attaches the forend to the upper receiver right ?
:confused:

Huh? That is the barrel nut. The buffer tube is the tube the recoil spring and buffer are contained in. It is also where the stock attaches

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