M&P 14 sport receiver extension 6061 or 7075 aluminum

[modelbuilder56]

Hello all,
I'am new here so excuse me if this has been asked before. I contacted Smith and Wesson and they could not tell me the answer. I know the diameter of the "buffer tube" is 1.145 which makes it mil spec but what trouble me is if it is 6061 aluminum and not 7075, does anyone know for sure?

that should have read M&P 15 not 14 sorry

thanks

 

[Rastoff]

I'm no metallurgist, but I gotta ask, does it really matter? I have no idea what any of my buffer tubes are made of and none have failed.

 

[MichiganScott]

I find it totally irrelevant. Besides, specifications change.

 

[modelbuilder56]

It might be relevant if you drop your rifle on the receiver extension and it breaks because it is the weaker 6061. 7075t6 is 66% stronger than 6061 and the "buffer tube" is actually under quite a bit of stress. I find it odd that S&W can't provide this information when alot of the other manufacturers do.

 

[Rastoff]

Weaker is relative. Again, I'm not a metal guy, but there is a balance between strength and flexibility. I've seen super strong materials break where a more flexible piece didn't.

I have no idea what my buffer tubes are made from. Probably the weaker stuff because I didn't pay a premium for them. I have slammed them on the ground intentionally during demonstrations to show some others how the AR functions and why it was made the way it was. None have been damaged or bent through my usage. Of course, it's not nearly as hard use as actual combat.

If you don't have confidence in the tube that comes with the gun, it's easy to swap it out.

 

[cyphertext]

I believe the S&W to be 7075, and this is why. I have two rifles, the Sport and a CMMG Quebec. Both have "milspec" lowers, with "milspec" receiver extensions. However, the extensions are different, so I am pretty sure I have one that is truly milspec, and one that is milspec dimensions.

The difference is that the 6061 extensions are typically thicker. On my CMMG, right after the threads, there is a ridge where the tube gets thicker...

My S&W does not have this ridge. It is smooth and the tube is the same diameter, except the threads seem to protrude from the tube a little...

Pictures are examples found on the net, not actual pictures of my rifles...

 

[ChattanoogaPhil]

My S&W does not have this ridge. It is smooth and the tube is the same diameter, except the threads seem to protrude from the tube a little...
.

It's my understanding that mil-spec threads are rolled, resulting in the tube metal being displaced and pushed up for the threads. Commercial tube threads are cut and is why the tube has to be slightly larger in diameter. It seems odd that you could have tubes with identical diameters but one with threads taller than the diameter of the tube.

 

[cyphertext]

It's my understanding that mil-spec threads are rolled, resulting in the tube metal being displaced and pushed up for the threads. Commercial tube threads are cut and is why the tube has to be slightly larger in diameter. It seems odd that you could have tubes with identical diameters but one with threads taller than the diameter of the tube.

It might be an optical illusion more than anything. Or, it was almost midnight when I looked at it last night.

 

[modelbuilder56]

Thank you all for your input.

What I have learned so far from others is that the threads on a mil spec diameter extension are a little larger than the tube itself because after they are cut the tube is machined to the proper diameter making it 1.145 inches. I have also heard the interior color of the 7075 t6 tube is gray vs. black for the 6061t6 tube. I have a new BCM 7075t6 tube and it is indeed gray inside and the tube on the M&P 15 inside is black. I have a Colt 6920, DDM4v7 and this is my 2d M&P 15 . Out of all of my rifles I must say the M&P 15 is my favorite simply because the 1/9 twist shoots the lighter grain bullets more accurately. I have owned AR's for over 30 years but not until recently have I really understood their workings.
Just checked the interior color of the DD and Colt tubes and they are black so I do not think the color check is a way to discern the type of aluminum.

 

[ChattanoogaPhil]

Thank you all for your input.

What I have learned so far from others is that the threads on a mil spec diameter extension are a little larger than the tube itself because after they are cut the tube is machined to the proper diameter making it 1.145 inches. I have also heard the interior color of the 7075 t6 tube is gray vs. black for the 6061t6 tube. I have a new BCM 7075t6 tube and it is indeed gray inside and the tube on the M&P 15 inside is black. I have a Colt 6920, DDM4v7 and this is my 2d M&P 15 . Out of all of my rifles I must say the M&P 15 is my favorite simply because the 1/9 twist shoots the lighter grain bullets more accurately. I have owned AR's for over 30 years but not until recently have I really understood their workings.
Just checked the interior color of the DD and Colt tubes and they are black so I do not think the color check is a way to discern the type of aluminum.

Google- mil-spec receiver threads rolled.. and see what you find.

 

[modelbuilder56]

http://www.google.com/url?sa=t&rct=...=9tCWwDycP0zUsrHtHo2FeQ&bvm=bv.64507335,d.cWc
Tube diameter according to Pat Rogers is 1.150 with the thread diameter at 1.875 having the threads cut in with a lathe.

 

[ChattanoogaPhil]

There 18 bazillion hits for how mil-spec receiver extensions threads are rolled, not cut. How did you manage to find this dude blogging about a partial PM from someone else that he says he read?

 

[modelbuilder56]

First let me say that all I was looking for was an answer to a question Smith and Wesson couldn't answer and I thought someone here might have one. I called them and they told me they didn't know, two weeks ago I emailed them with no response at all. I don't want to ruffle anyone's feathers here as this rifle is a very fine rifle indeed. It is a tool that I use to protect myself and my families lives with and I would feel more comfortable knowing what the components are made from.
That google search is from Lightfighter tactical .com and that"guy" is Pat Rogers from EAG tactical and BCM so I think I would trust their information more so than non professionals who can blog about anything they wish.

 

[ChattanoogaPhil]

No ruffled feathers at all. I'm just curious as to what the real answer is, just like you.

 

[cyphertext]

This should add to the confusion...

On my Sport, the threads are flat, on the CMMG, they are peaks...

I don't have a clue what I have!

 

[cyphertext]

Also wanted to add...

After looking again today, both of my tubes have the ridge like in the picture above. It does not go all the way around the tube and is only there on one side.

So, both of my tubes look the same, with a ridge back behind the threads, but one has flat threads and one has peaked threads.

 

[ChattanoogaPhil]

Confusion is what Forums are all about.

Got an e-mail into BCM to see what they have to say.

Dan at LaRue Tactical just told me they roll the threads, not cut. I asked him if he was certain of it, he said yes. So I give that a 50/50 accuracy rating . The reason I doubt these type guys who answer the phone is they are likely to just want to get you off the phone. A while back I tortured the poor guy at Yankee Hill until he told me they got their BCGs from Stag and they were not necessarily HPT/MPI. Hey, that costs $5 extra.

 

[modelbuilder56]

Confusion is what Forums are all about.

Got an e-mail into BCM to see what they have to say.

Dan at LaRue Tactical just told me they roll the threads, not cut. I asked him if he was certain of it, he said yes. So I give that a 50/50 accuracy rating . The reason I doubt these type guys who answer the phone is they are likely to just want to get you off the phone. A while back I tortured the poor guy at Yankee Hill until he told me they got their BCGs from Stag and they were not necessarily HPT/MPI. Hey, that costs $5 extra.

I knew I would get positive response from this forum and I thank you. I purchased my first sport over a year ago and recently got this one. I knew the tube was of mil spec diameter last year when I changed stocks but until recently I didn't know they could be made from either the 6061 or 7075 material. I'am not in any way a "mil spec" junkie, I don't care if my BCG is a semi auto profile, twist rate is 1/9 and barrel is not chrome lined, I do however have the need to know what materials my rifle are made from.

 

[ChattanoogaPhil]

Well... BCM is at least trying to answer. And I really appreciate the clarification of "buffer tube"

The non-answer was...

Q: Are your mil-spec receiver extension tube threads cut or rolled?

A: Hi Phillip

Here are the full specs of the BCM Milspec Receiver Extension (Buffer Tube) 6 Position.

Milspec Receiver Extension (Buffer Tube)

-----------
My reply was...

Thanks, but that does not answer the question.

ARE THE THREADS ON THE MIL-SPEC RECEIVER EXTENSION TUBE ROLLED OR CUT?

---------

We'll see.

 

[modelbuilder56]

Just off the phone with the good folks at DD, they told me their threads are cut with a machine, possible some cut and some roll? This still doesn't answer the material question though I have a BCM tube and before I start wrenching I thought I'd ask here.

Not taking anything away from BCM but they assemble rifles from bought components where some manufacturers actually machine parts in house like DD but I know they don't make everything in house .