6061: further thoughts and new information

I only partially agree...$300 is alot of money to some people. No slight meant against NEA here...but I'd like to see people get what they can afford and if that means Norc than so be it. If they can pony up for an NEA than great...or how about only $200 more and then an LMT...see where I'm going with this? AR's have a huge price range...
 
Hawkmoon,

No worries, I'm pretty sure this thread is full of comments that were posted in the heat of the moment. If we lost sleep about what people posted on the net we would all be insomniacs. As I also work shifts, I already feel like an insomniac some of the time anyway.

At least misanthropist managed to keep his head, and the whole point of this thread was to get some information from NEA to allow people looking to purchase an AR to do so using as many facts as they feel necessary.

Regards.

Mark
 
misanthropist said:
I was really surprised how fast the response was; I had expected to get on here today and say, "I would like to ask everyone to be patient and not interpret a bit of a wait as stalling".

I thought it would be a week before I heard back and I thought the answers would be possibly vague enough that I would have a lot of follow-up work to do and that I would have to pry a bit.

But the answers are pretty complete and direct. I may have some follow up stuff but in general the response was better than I had hoped.
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So lets see the Q&A...
 
This is one of the most informative, level headed (for some) thread that I've seen in some time. Very interesting.

I've also noticed that since the thread began that NEA has changed the barrel steel spec from 4150 to 4140CMV.

NEA have made some interesting choices with their rifles and certainly seem to be offering good value for the money but I do wonder why they've made some of the choices that they have.
 
Leg said:
This is one of the most informative, level headed (for some) thread that I've seen in some time. Very interesting.

I've also noticed that since the thread began that NEA has changed the barrel steel spec from 4150 to 4140CMV.

NEA have made some interesting choices with their rifles and certainly seem to be offering good value for the money but I do wonder why they've made some of the choices that they have.
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Where did they change it to 4140 CMV? It looks like they clarified it was 4150CMV as opposed to plain 4150.
 
4140cmv

Claven,

It's now up on their web page under the barrel description.

Misprint?

Guess we'll see when misanthropist posts the specs.

Regards.

Mark
 
The error was on my part. Somewhere along the line there was a misprint and I carried it on. They are in fact 4140 CMV as confirmed by our blank supplier. I updated our specs as soon as I confirmed, not when Misant was to post his answers.
 
For material strenght, engineers usually look at "yield strength", which material starts to deform plastically, not the Young Modulus.
 
Also, almost all steels have virtually the same modulus of elasticity, at around 210 GPa. You're right MUGEN. Having a high UTS is pointless if your yield strength is low.

Fatigue strength, toughness, red hardness, hardness, malleability and ductility are just a few of the things one needs to consider in barrel material. NEA hasn't reinvented the wheel, and I believe their selections in materials used in their AR to be sound.
 
MUGEN said:
For material strenght, engineers usually look at "yield strength", which material starts to deform plastically, not the Young Modulus.
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obviously true, but if I am understanding things correctly, the Young's Modulus should give an idea of the general stiffness or rigidity of the material. My concern is not really that the 6061 would actually fail, but how it would hold up during normal usage. I think that can be represented well by examining the response of the aluminum to loading.

But I am not an engineer.
 
misanthropist said:
obviously true, but if I am understanding things correctly, the Young's Modulus should give an idea of the general stiffness or rigidity of the material. My concern is not really that the 6061 would actually fail, but how it would hold up during normal usage. I think that can be represented well by examining the response of the aluminum to loading.
.
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Young's modulus does indeed express stiffness, as elastic deformation vs. applied load so long as you remain within the elastic limit, but I am scratching my head as to how that could possibly reflect anything about practical performance in an application like a rifle. The only measure that matters is, when you applied a load to it did it break (or bend)?
 
Been reading quite a bit about this, and Young's modulus, in my understanding, in basic terms measures elasticity.

So if you took a fore end rail made from 6061 and one of 7075 and stuck each end on a block of wood, and stepped on the middle of each rail, you could use this.

Or if you grabbed each end of the rail and tried to stretch it, you could use this.

What Young's modulus doesn't measure, is if you took those same two rails and smacked them against a rock, which one would come out of it better.

I think that can be represented well by examining the response of the aluminum to loading.
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A BCG travelling back and forth inside the upper, doesn't load it.

It's not the same as the load placed on an aircraft wing.

This is my understanding but like yourself, I'm not an engineer either.
 
BattleRife said:
Young's modulus does indeed express stiffness, as elastic deformation vs. applied load so long as you remain within the elastic limit, but I am scratching my head as to how that could possibly reflect anything about practical performance in an application like a rifle. The only measure that matters is, when you applied a load to it did it break (or bend)?
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I don't know. I am reliant in this regard on other engineers to whom I spoke while looking in to this subject.

But I will be the first to admit that I don't know how accurate a description that is. I am not in any position to argue with engineers about any of the following:

a) what the most relevant description of stress loading on a material is

b) how much stress an AR upper is subjected to

c) how close a 6061 upper will come to exceeding the limits of the material

I don't know. I spoke to a number of informed people about this before writing anything on the subject at all, because I was concerned about it.

The general feedback I received was, "if you have a problem, it will be that the 6061 wears too quickly in the pin holes". Nobody was concerned about ultimate strength or catastrophic failure.

But as I say I am only synthesizing the information I received. I am not a materials engineer. I am not a firearms designer. I am a guy who has shot a lot of guns, a lot, and writes about things. That's it.
 
Farmboy said:
Been reading quite a bit about this, and Young's modulus, in my understanding, in basic terms measures elasticity.

So if you took a fore end rail made from 6061 and one of 7075 and stuck each end on a block of wood, and stepped on the middle of each rail, you could use this.

Or if you grabbed each end of the rail and tried to stretch it, you could use this.

What Young's modulus doesn't measure, is if you took those same two rails and smacked them against a rock, which one would come out of it better.
Click to expand...

I believe this to be a pretty good description as well, based on my understanding of the information I was given.
 
Youngs modulus describes as you said stiffness. On a stress-strain diagram it relates to the linear part of the curve, below the yield point. It describes how much load it takes to deform the material (elastic deformation only). 6061 and 7075 are both aluminums and their modulus of elasticity is around 70 GPa. Steels are around 210 GPA. This will vary a GPa or two depending on alloying elements and heat treating.

So although the density of aluminum is approx 1/3 that of steel, it will. Deflect 3 times more than steel if the same sized specimen was subjected to equal loading. So it's lighter but deflects more.

Now hitting it against a rock and it surviving would be a function of hardness and toughness.
 
Throttle_monkey1 said:
Now hitting it against a rock and it surviving would be a function of hardness and toughness.
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What you need to be looking at here is Yield Strength and Ductility. You would need a stress-strain curve for each alloy. Another way of putting it is by looking at the alloy's ability to absorb mechanical (kinetic) energy up to the point of failure.

A quick and dirty lab test would be to prepare two identically sized samples of both alloys, anodize them using the NEA process, and then destructively test both samples using the charpy method.

Let me save you the anticipation though... the difference between the two will be, for all practical intents and purposes, negligible.
 
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