I know 7075 is the standard for AR uppers and lowers. But is this standard really needed to ensure the proper function and longevity of the rifle? Do the uppers and lowers need to be made of 7075 or is it just a waste of more expensive alloy? Would a properly coated and machined 6061 hold up just as well?
Your thoughts greatly appreciated.
From everything that I have read and experienced 7075 is far superior to 6061 in terms of strength and wear. Uppers and lowers seem to outlast almost every other component, so why skimp? At the most you would save what, $60 - $80 for an entire rifle?
I am of the opinion that the quality of the machine work is more important than the difference between 7 and 6 series aluminum.
That being said, you can get a Vltor upper which is made from a 7 series forging and is amazingly accurate in its dimensions. Perfect alignment to a DD RIS-II, and no windage correction needed when used with a Noveske barrel and a Short Dot in a Larue mount.
When you use parts which are dimensionally perfect, it’s much easier to zero your weapon.
^^That’s an interesting statement.
I’m just wondering about the typical wear points in the upper receiver and the pin holes in the lower. Is the use of 7075 just a hold out from an antiquated military spec?
It wouldn’t matter much to most consumers but it would matter greatly to the manufacturer where profit margins are thin. If using 6061 is cheaper with no loss in performance of the rifle, then it’s a sound business decision.
The 6 series is easier on the tooling too. Harder metals eat tooling like crazy.
This was my 50 yard zero target with 5.56mm TAP. No windage correction.
Next range trip I’m going to move to a 100 yard zero.
I will only use Larue or Vltor uppers. Being dimensionally accurate is much more important that material difference.
While it IS true that fit and finish are paramount, the rigidity of an upper made of 7075 is much greater than an identical design of 6061. The lower also benefits, ever look at the area where the receiver extension threads in? Thin cross sections like that gain significantly by being a superior alloy.
Sure a 6061 model will probably suffice in most situations but material costs and tooling life don’t warrant the compromise in my opinion.
Now Forged vs. Billet…
Interesting thread, from a Canadian perspective at least. Of course I have no idea what generated this question…
I suspect it is a non-issue but I struggle with this as well. Instinctively my reaction to the use of 6061 is bad.
However, properly treated, I wonder if the 6061 really gives up all that much?
My concerns may be more based in the fact that typically, companies that have used these materials have cut corners that really DO matter.
Much like the finish under the FSB…it may not matter at all from a user perspective, and simply be indicative of a company which, generally speaking, doesn’t give a shit. But if a company does everything else bang on, are you going to avoid them because they don’t think there’s a point to putting a finish on the barrel before they mount the FSB?
Anyway, hopefully some more materials-expert people will give their thoughts.
This has been nagging at me for a while. I’m hoping the quality of debate is better here and that members have some firm data or insights on this topic. We all know that 7075 is more durable, but is it really necessary in this application?
Its a buyers market. I would choose 7 series over 6 series, and forged over billet.
The only way I would take a 6 series billet over a 7 series forged, provided machining was equally high quality, was if the 6 gave me some feature I had to have. But I don’t think such a situation exists. I don’t even really see a significant cost difference between the two.
You can get a Vltor upper which is perfectly machined off of a 7 series forging.
Barrel steel…that’s amost another thread. If its 416, 416R, 4140, LW50, CMV or the like, everyone will have tons of reason to tell you why theirs is the best. Again, I think this comes down to what the finish manufacturer is doing, provided the blanks they get are of high quality.
Some of the material content effects how the barrel is machined, life of the tools use etc. If one barrel can be machined easier with a better finish, it may be a result in a better product and an improved price point.
the upper and lower arent the primary stress components. When a round is fired the bolt, barrel, and barrel extension take all all the force. The upper is essentially a housing to hold the barrel, gas tube, charging handle and bolt carrier group, thats why its made out of aluminum and not steel.
Maybe not primary, but still important.
There was a high speed video on YouTube where you could see the upper flex with each shot.
In theory, as long as any flex action was repeatable, it flexed the same and returned to te same position everytime, this wouldn’t effect group size in the short term. Over the long term, maybe there’s a fatigue issue. Again, just theory.
For any accuracy based upper, I would only use a Vltor receiver. Of course the trade off is cost and weight over a standard forging. But you get what you pay for…
7075 aluminum has a harder surface than 6061 Especially when anodized, 7075 has a much harder surface. With 6061, threads are softer which makes them easier to cross thread and will distort at a lower torque. Trigger pin holes will wallow out faster
While 7075 is harder than 6061, machine tool life is still good When machined before heat treating, aluminum alloys are very easy to machine. Even after heat treating, aluminum is a breeze to machine compared to steel
7075 is stiffer than 6061 During firing, 7075 will flex less than 6061. 7075 also is less ductile and less prone to bending
Receivers made of 6061 are billets I do not know of any 6061 receivers that are machined from forgings. Billet receivers cost more and pound for pound are weaker than forged.
7075 is a better alloy for making forgings Receivers are made from 7075 forgings because they cost less, have greater strength, are more rigid, offer greater durability of threads and trigger pin holes, than any receiver made from 6061, not because of some antiquated material specification
Buying a receiver made of 6061, especially made from a billet, is paying more for less and makes no sense
Seeing as some like to say aircraft grade this or that…
End of STORY!
This is why the military uses Forged receivers…
A beat to hell Mil Upper before restore/rebuild…
7075 is a significantly superior material I have used and machined both 6061 and 7075 tool wear is almost a non factor when using either material. Also, we find 7075 easier to machine because it is less gummy than the 6061. However, 7075 sells for less with the scrap man due to it being less pure than 6061.
7075 Mechanical Properties
Hardness, Rockwell 53.5
Ultimate Tensile Strength 83000 psi
Tensile Yield Strength 73000 psi
Elongation at Break 11 %
6061 Mechanical Properties
Hardness, Rockwell 40
Ultimate Tensile Strength 45000 psi
Tensile Yield Strength 40000 psi
Elongation at Break 12 %
I’m assuming this is why Clobb asked the question here:
http://northeasternarms.com/platforms-1
Asking the question on Canadiangunnutz will at best get you jumped by the NEA fanboys, and banned at worst.
For me, the question is answered above by a combination of what mistwolf and mrwetwork posted. It may not be required, but why use parts made from 6061 billet, when you can have 7075 forgings for not much more. Looking at those figures, I mean wow!
Regards.
Mark
Actually, that question has been asked on CGN. No bans were instituted.
I know because the discussion occurred in my thread, where I started talking about the NEA guns, back before the project was common knowledge.
I commented on this exact issue myself, and said that I had a hard time taking 6061 when 7075 was the standard. I consider it a step down in materials strength and whether it matters or not, I don’t like it.
And nobody gave me a hard time about it at all.
And Greentips (owner of the site for those who don’t know) talked about it extensively, and said he’d rather have 7075. He did not seem interested in banning himself afterwards but it is difficult to say for sure.
At any rate, I am interested to hear continued debate on 6061 vs 7075, but I don’t think there is all that much of a debate. 7075 is preferred. 6061 is probably adequate and I believe that older Colts were made of 6061.
But I would take 7075 if I could. There is always the option of swapping out the upper, of course.
But it frustrates me that NEA has chosen to go with 6061, even if their reasoning is correct. Their position is that their engineers have determined that 6061 is a good material for their demands, and that 7075 is unnecessary and I don’t doubt that they have a point. But I have a hard time taking a step down in materials strength, necessary or not.
Thread hijack…
It’s not so much asking the original question, but calling out a forum sponsor when they respond with the marketing BS and outright garbage that I have seen posted on CGN probably will. But that would, and has, happened on TOS and other similar forums too.
Do you think they would get away with some of their replies here, or better yet, forums like LF?
I’m not interested in turning this thread into a CGN/NEA bashing exercise, as quite frankly I would never purchase one of their rifles, and I don’t care how other people choose to spend their money, but I do have a severe allergy to BS.
End of thread hijack.
Regards.
Mark
Assuming that the firearms are used exactly as intended there is no issue with 6061. For example… dry firing a complete lower receiver that is made of 7075 will result in almost 0 deformation of the metal between the FCG and the bolt catch. Whereas with 6061 there will be immediate deformation in 10-15 fires. The metal there is only ~.093 thick. Does that affect the performance? No, there is plenty of clearance on both sides and if you dry fire with it in complete rifle configuration the firing pin/bcg limit the hammer from smacking that wall.
Also, from a production aspect when making these out of billet it costs you roughly 100% more to manufacture from 7075 than 6061. Most companies do not have the coin to make a mold for 7075 forgings.
My favorite thing about the AR-15 is that most of the parts are not under heavy stress. It is a very smooth system. The upper receiver really is just a housing to allow the bcg to move about. As is the buffer tube. There are no real extreme forces going on there. The most extreme forces are in the chamber, through the gas port and into the gas block where they start bleeding off.