View Full Version : Billet Upper and Lower Made Of 6061 Aluminum?
Clobbersauras
11-14-11, 17:50
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.
Clobbersauras
11-14-11, 20:41
^^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?
Clobbersauras
11-14-11, 20:46
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?
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.
http://img.photobucket.com/albums/v340/roguedemon/fb36f850.jpg
I will only use Larue or Vltor uppers. Being dimensionally accurate is much more important that material difference.
apexcncshop
11-14-11, 21:25
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...
misanthropist
11-14-11, 22:16
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.
Clobbersauras
11-14-11, 22:35
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.
ForTehNguyen
11-14-11, 22:58
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?
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
Travelingchild
11-15-11, 07:25
Seeing as some like to say aircraft grade this or that..
http://www.aircraftspruce.com/catalog/mepages/aluminfo.php
Buying a receiver made of 6061, especially made from a billet, is paying more for less and makes no sense
End of STORY!
This is why the military uses Forged receivers....
A beat to hell Mil Upper before restore/rebuild..
http://i210.photobucket.com/albums/bb201/trixiebud/CIMG3728.jpg
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
misanthropist
11-15-11, 12:22
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
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.
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.
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
Exactly right. I see no benefit to using the billet receivers on the market that are advertised as "precision" receivers, ever.
The standard lower and upper forging is fine.
Seeing as some like to say aircraft grade this or that..
http://www.aircraftspruce.com/catalog/mepages/aluminfo.php
"Aircraft Grade" is buzz term used to decive people.
Almost all types of aluminum can be called "aircraft grade".
Most of the lower grade AL is used in non structural applications such as seat mounts, cockpit panels, and other fixtures.
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.
I have to strongly disagree. Dry firing a lower without an upper or dry firing block won't distort a 7075 lower, but it will cause cracks. 7075 is stiffer and very much less ductile than 6061. If you understood the properties of aluminum alloys better, you would see that the difference between 7075 & 6061 do matter in this application. Trigger pin holes and receiver extension threads will last much longer when a lower is made from 7075. Where the receiver extension meets the body of the lower is a stress riser. 7075 will resist deflection better. 6061 will be easier to bend as that's what that alloy was developed for- tighter bends without cracking and weld-ability. Aluminum is a fantastic material but it's critical to choose the right alloy for the job.
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.
Few companies have the dies to forge AR receivers. If I understand it correctly, there are three sources of forgings. (Forgings are made from dies, not molds.) Most companies source the raw forgings from one of these companies and perform their own machining or sub-contract it out. If you check the prices of billeted receivers, you will see they cost more than most of the quality receivers machined from forgings, regardless of alloy type
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.
They may not be under stress from the chamber pressure, as all of that is contained within the barrel, barrel extension and bolt. But the upper does flex during firing and from the weight & leverage of the barrel. A 6061 upper is more likely to permanently distort where it must hold the barrel than one made of 7075. 7075 will also resist battering much better than 6061.
6061 is a great alloy for what it was developed for. But it offers zero advantages over 7075 for making AR receivers in performance or cost and more disadvantages than you can shake a set of KNS anti-rotation pins at
"Aircraft Grade" is buzz term used to decive people.
Almost all types of aluminum can be called "aircraft grade".
Most of the lower grade AL is used in non structural applications such as seat mounts, cockpit panels, and other fixtures.
You're correct that "aircraft grade" is nothing more than a buzzword. "Aircraft grade" doesn't mean it's certificated for use in aviation.
Just a note- While airline seats and flight crew seats are lacking in comfort, their frames and mounts are anything but low grade. We cannot risk having them breaking loose or the seat belts failing and having the seats and people flailing about when the aircraft encounters rough flying conditions
I have to strongly disagree. Dry firing a lower without an upper or dry firing block won't distort a 7075 lower, but it will cause cracks.
We're agreeing here, 6061 will distort. 7075 may crack, but I can't see it happening. I did a test with over 12,000 dry fires on a lower and there was no issues at all.
7075 is stiffer and very much less ductile than 6061. If you understood the properties of aluminum alloys better, you would see that the difference between 7075 & 6061 do matter in this application.
My point was it is "good enough" and would last under normal use and circumstances. I understand the properties of aluminum plenty.
Trigger pin holes and receiver extension threads will last much longer when a lower is made from 7075. Where the receiver extension meets the body of the lower is a stress riser. 7075 will resist deflection better.
Again, we are on the same side I am agreeing 7075 is a more suitable material but 6061 can do the job. Not that it is perfect for the job, but can do it.
6061 will be easier to bend as that's what that alloy was developed for- tighter bends without cracking and weld-ability. Aluminum is a fantastic material but it's critical to choose the right alloy for the job.
Again, see response above.
Few companies have the dies to forge AR receivers. If I understand it correctly, there are three sources of forgings. (Forgings are made from dies, not molds.) Most companies source the raw forgings from one of these companies and perform their own machining or sub-contract it out. If you check the prices of billeted receivers, you will see they cost more than most of the quality receivers machined from forgings, regardless of alloy type
Yes, I am quite aware that few companies actually do pony up the cash for a die. I also am aware that it is a "die" but for sake of general understanding I replaced it with mold.
My point was that the pricing structure on a per piece cost basis is as follows in regards to the expense of the raw material used to manufacture the parts.
In an order of most to least expensive (raw materials):
7075 Billet
6061 Billet
7075 Forged
They may not be under stress from the chamber pressure, as all of that is contained within the barrel, barrel extension and bolt. But the upper does flex during firing and from the weight & leverage of the barrel. A 6061 upper is more likely to permanently distort where it must hold the barrel than one made of 7075. 7075 will also resist battering much better than 6061.
My point was the stresses are minimal in relative comparison. I personally can not see permanent disfigurement happening to the upper receiver and would be interested to find a way to quantify this.
6061 is a great alloy for what it was developed for. But it offers zero advantages over 7075 for making AR receivers in performance or cost and more disadvantages than you can shake a set of KNS anti-rotation pins at
Completely agreeing. It can be used, but 7075 is more suitable for the job.
...I personally can not see permanent disfigurement happening to the upper receiver and would be interested to find a way to quantify this...
I don't know that a 6061 receiver will deform from normal usage, but it will deform easier if or when extraordinary stresses are place on that area. Considering what I see on aircraft, I do not think 6061 is "good enough" for an AR receiver and is the wrong application for the alloy.
While 6061 may be cheaper to acquire than 7075, the bottom line is the lower receivers that cost the least and are within spec and of good quality are made from 7075 forgings, including (but not limited to) those offered by Aero Precision, LRB, Palmetto and Surplus Ammo & Arms
While 6061 may be cheaper to acquire than 7075, the bottom line is the lower receivers that cost the least and are within spec are made from 7075 forgings, including (but not limited to) those offered by Aero Precision, LRB, Palmetto and Surplus Ammo & Arms
Yep, forgings are the best and most affordable. You're just limited to what you can do based on the shape of the forging. So if you want outside the box stuff so to speak it requires use of trickery.
That's a good point. I'd love to try the new AX556 billeted ambidextrous lower, but it's more than I can afford at the moment. Matter of fact, it's the only billeted lower I find at all interesting
Clobbersauras
11-15-11, 17:52
Thanks for the responses guys. I appreciate it. This debate has, as I feared, devolved into a "7075 billet is a better material for the job" thread. I think we all agree that 7075 is better.
But....that is like saying that inconel is a better material for a muzzle brake, which it is. But it's not necessarily needed in "most" applications. Other lesser quality materials can be used that provide more than adequate performance.
The question I'm interested in answering: Is 6061 is a suitable material for this application? Will it's wear properties give good longevity to the system before parts start to fail?
This thread and others gives me the impression that this question has never really been put to the test. So far I haven't seen anything in this thread or others to prove that 6061 shouldn't be used. The only real data I have found is from a manufacturer of such a system and others who have shot it. So far, all the reports have been favorable.
Would someone please close this stupid ****ing thread/waste of bandwidth before I beat my head against the wall.
I think that its been stated plenty. 6061 PROBABLY would do the job. You know that its going to wear out faster than 7075 already. You don't have to even say its a guess. By how much? Who knows. Depends on how well its made and if there are no defects. Since I don't think anyone can tell you how long 7075 is going to last and by far the most tested I don't think your going to get the answer your digging for. The real statement made that I feel holds more weight is why would you want lower grade al for more? I think markm and other senior members have answered and you didn't get the answer you wanted. Hope that helps.
Clobbersauras
11-15-11, 18:46
Would someone please close this stupid ****ing thread/waste of bandwidth before I beat my head against the wall.
C'mon tell us how you really feel. Don't hold back.
misanthropist
11-15-11, 18:53
The real statement made that I feel holds more weight is why would you want lower grade al for more?
This is something I can answer: there is no domestic supply of ARs in Canada...or there wasn't really, until now.
There is now a company which offers a pretty solid AR, but with 6061 upper and lower receivers.
Typically Canadians pay around $2-3000 for a Daniel Defense or Colt.
The new ARs have been released for about a thousand bucks, including 12" FF rail. So as you can imagine there is a fair degree of interest.
Uppers and lowers based on 7075 forgings are common as dirt in the US. Here, they must be imported. If you have ever attempted to export guns from the US, you know that it's expensive and generally a pain in the ass. This goes for major components like uppers and lowers as well. So having a domestic supply means they are much, much cheaper.
So while in the US it would be paying more for less, in Canada it's paying less. The cost of the billet upper and lower here, relative to a forging, is much lower. So our situation is somewhat different.
At any rate, I think that the question has been answered about as much as it can be answered, unless anyone has historical information on the change from 6061 as used in the XM16e1 to 7075 used in later models.
Even then I am unsure if the information would be complete, as this assumes that the processes the uppers and lowers were put through were the same as NEA's process, which is probably not the case.
But whether that makes a significant difference, I couldn't say.
Clobbersauras
11-15-11, 18:59
I think that its been stated plenty. 6061 PROBABLY would do the job. You know that its going to wear out faster than 7075 already. You don't have to even say its a guess. By how much? Who knows. Depends on how well its made and if there are no defects. Since I don't think anyone can tell you how long 7075 is going to last and by far the most tested I don't think your going to get the answer your digging for. The real statement made that I feel holds more weight is why would you want lower grade al for more? I think markm and other senior members have answered and you didn't get the answer you wanted. Hope that helps.
I appreciate the members responses, but what I was hoping for was some data or first hand observations of 6061 upper/lowers that have been put through serious use and how they held up. Perhaps this information is just not available.
Misanthropist's post above clarified why I started this thread. I have no dog in that fight, and it's why I didn't specifically reference them. I was just trying to understand their decision to use that material.
If it's all our Canadian friends have a available, it's a case of "We've got what we've got". Although not ideal, 6061 will work well enough. Be careful when changing receiver extensions and barrels, threads cut into 6061 are soft and seem to have a limited number of times they can be torqued before they fail. Given a choice between a 6061 billet receiver and one molded from plastic, the superior choice is clearly the 6061 billet
This is something I can answer: there is no domestic supply of ARs in Canada...or there wasn't really, until now.
There is now a company which offers a pretty solid AR, but with 6061 upper and lower receivers.
Typically Canadians pay around $2-3000 for a Daniel Defense or Colt.
The new ARs have been released for about a thousand bucks, including 12" FF rail. So as you can imagine there is a fair degree of interest.
Uppers and lowers based on 7075 forgings are common as dirt in the US. Here, they must be imported. If you have ever attempted to export guns from the US, you know that it's expensive and generally a pain in the ass. This goes for major components like uppers and lowers as well. So having a domestic supply means they are much, much cheaper.
So while in the US it would be paying more for less, in Canada it's paying less. The cost of the billet upper and lower here, relative to a forging, is much lower. So our situation is somewhat different.
At any rate, I think that the question has been answered about as much as it can be answered, unless anyone has historical information on the change from 6061 as used in the XM16e1 to 7075 used in later models.
Even then I am unsure if the information would be complete, as this assumes that the processes the uppers and lowers were put through were the same as NEA's process, which is probably not the case.
But whether that makes a significant difference, I couldn't say.
Right on dude. In that case I would gladly buy it. If it a third of the cost its still easier to manage. Other than the fact that you may worry in an hd situation. Realistically if you think about the hd portion imho your not going to be doing mag dumps. However I do understand the concern for durability.
On another note I hope that the Canadian government comes to understand the common sense of these scary black rifles. I think its completely asinine that you may only own the rifle for ranges yet your allowed to have any length barrel you may wish. Unless that changed recently which I heard it might. Then again I like many don't feel its right of the government to have any say in the legal purchasing of any firearm by an honest person. I also apologize for not being fully informed of your laws.
I appreciate the members responses, but what I was hoping for was some data or first hand observations of 6061 upper/lowers that have been put through serious use and how they held up. Perhaps this information is just not available.
Misanthropist's post above clarified why I started this thread. I have no dog in that fight, and it's why I didn't specifically reference them. I was just trying to understand their decision to use that material.
While this is merely speculation and know that I am not trying to state anything concrete I would guess that the company may have used this steel as a cheaper substitute for the pupose of having enough money to flood the Canadian market. It would make sense if this company is the only one selling ar 15s. Regardless if you agree or not it was a huge business advantage to dpms to have lower standards as it is faster to produce for less. Which is why o feel there ARE SO MANY. Of course us informed consumers know better but we all know that most ar owners are not.
misanthropist
11-15-11, 19:56
Just to be clear, there are many sources of ARs...just not much in the way of domestic ARs.
We can buy LMTs and DDs and so on...we just pay 2-3 times what you guys pay. And, frequently, the guns are in "export" condition which means no collapsible stocks, no muzzle devices...or sometimes it means they are intact...very difficult to predict that the US ITAR people will let us have.
Strange stuff, anyway.
6061 is a great alloy for what it was developed for. But it offers zero advantages over 7075 for making AR receivers in performance or cost and more disadvantages than you can shake a set of KNS anti-rotation pins at
Agreed. I'm not an engineer but have abused many products made from different grades of aluminum for the same application. If it's something that clamps/flexes, use 6-Series. If you use 6 and it has threads, they better be helicoiled or use a nut on the other side. If you want stiffness/strength and good wear use 7. This all leads me to believe that 6 is poor choice for an upper, lower or receiver extension.
the upper and lower arent the primary stress components.
I understand what you are saying, but what if you drop the weapon from a high place, step on it by accident, etc? I've seen many pics of broken receiver extension made of shitty AL. If you were to build a gun with a Colt RE and an inferior AL upper/lower, what would break then?
Suwannee Tim
11-15-11, 20:36
.... the rigidity of an upper made of 7075 is much greater than an identical design of 6061. .....
The rigidity of 7075 and 6061 are virtually the same. Don't take my word for it, look it up for yourself. The number you are looking for is the Young's modulus (http://en.wikipedia.org/wiki/Young%27s_modulus) or elastic modulus and is in the range of 10X10^6 PSI for aluminum, any alloy. Why do you waste our time holding forth on a subject you know nothing about?
Travelingchild
11-15-11, 20:54
"Aircraft Grade" is buzz term used to decive people.
You're correct that "aircraft grade" is nothing more than a buzzword. "Aircraft grade" doesn't mean it's certificated for use in aviation...
Actually agree with both, forgot to convey my sarcasm,
It ranks right up there with "tactical" in marketings.
MistWolf.. Boeing?
misanthropist
11-16-11, 00:24
The rigidity of 7075 and 6061 are virtually the same. Don't take my word for it, look it up for yourself. The number you are looking for is the Young's modulus (http://en.wikipedia.org/wiki/Young%27s_modulus) or elastic modulus and is in the range of 10X10^6 PSI for aluminum, any alloy. Why do you waste our time holding forth on a subject you know nothing about?
I am interested to hear further information on this subject from you if you have more thoughts on it.
I'll be buying one of the all-6061 ARs, anyway, so it's mainly a matter of interest for me. But I do like information.
...Boeing?
Once upon a time, in Long Beach California. Built C-17s and MD-11s. Of course, when I hired on, it was McDonnell-Douglas. Later, we were bought out by Boeing. Currently working at ATS in Washington on 737s flown by Southwest Airlines
"Aircraft Grade" is buzz term used to decive people.
Almost all types of aluminum can be called "aircraft grade".
Most of the lower grade AL is used in non structural applications such as seat mounts, cockpit panels, and other fixtures.
Similar to the "mil-spec" term always being thrown around. Kinda like "these dpms parts will fit in a colt so they must be mil-spec!"
Suwannee Tim
11-16-11, 04:42
I am interested to hear further information on this subject from you if you have more thoughts on it.
I'll be buying one of the all-6061 ARs, anyway, so it's mainly a matter of interest for me. But I do like information.
The stiffness of an item depends on two things, it's dimensions and the Young's modulus of the material. The Young's modulus of ALL aluminum alloys is ten million PSI, it will vary slightly from alloy to alloy but only slightly. Ten million PSI for the softest 1000 series aluminum to the hardest 7000 series. Same with steel, the modulus of steels is thirty million PSI. Again, it will vary slightly with the alloy but not to any significant degree. Same with most any other metal and most other non-metals.
Something else, I am highly skeptical of the assertion that the anodized surface of 7075 is much harder than that of 6061. I want to see some test results. This is, after all, the internet where folks will make up a "fact" and where folks who have no idea what they are talking about talk about it anyway. I occasionally try to embarrass such "experts" but it usually doesn't work.
Clobbersauras
11-16-11, 07:28
^^So if I understand you correctly, the anodizing process may uniformly set the surface hardness of both types of aluminum?
Something else, I am highly skeptical of the assertion that the anodized surface of 7075 is much harder than that of 6061.
As long as it is true mil-spec hard coat it can not be any different. It has to meet the requirements regardless of the material underneath it.
The stiffness of an item depends on two things, it's dimensions and the Young's modulus of the material. The Young's modulus of ALL aluminum alloys is ten million PSI, it will vary slightly from alloy to alloy but only slightly. Ten million PSI for the softest 1000 series aluminum to the hardest 7000 series. Same with steel, the modulus of steels is thirty million PSI. Again, it will vary slightly with the alloy but not to any significant degree. Same with most any other metal and most other non-metals.
Something else, I am highly skeptical of the assertion that the anodized surface of 7075 is much harder than that of 6061. I want to see some test results. This is, after all, the internet where folks will make up a "fact" and where folks who have no idea what they are talking about talk about it anyway. I occasionally try to embarrass such "experts" but it usually doesn't work.
Be skeptical all you want. Years of experience has shown me that anodized 7075 is more resistant to fretting, abrasion and elongation of holes than anodized 6061 or anodized 2024. You can also "Young's modulus" all you want, but there's a reason why high stress aircraft parts are made from 7075 instead 6061 and there is a reason why some parts must be forged or extruded instead of cast, machined from a billet or bent
misanthropist
11-16-11, 16:13
For the record, the position of the manufacturer is that 7075 makes superior forgings, but that 6061-T6 makes better milled parts.
Additionally, receiver walls are thicker on their 6061 receivers than on a standard 7075 receiver.
As I have tried to keep clear, this is entirely outside my field of expertise. I will say that the manufacturer has a lengthy history of successful aerospace manufacturing including, I believe, work on the landing gear of the F18.
They are also partnered up with Troy, who has traditionally built quality parts in my view.
And, finally, the guns are warranteed for life. So either the manufacturer is shrewdly assessing the milquetoast performance demands of the average AR owner and knows that virtually nobody even takes up Vulcan on their warranty (I am assuming Vulcan warranties their guns) so they sure won't be wearing out something half decent, or they aren't worried that there will be an issue.
I guess I will just measure the ID of the pinholes and so on periodically and report back every few thousand rounds if there's anything interesting to note.
Suwannee Tim
11-16-11, 16:34
Be skeptical all you want. Years of experience has shown me that anodized 7075 is more resistant to fretting, abrasion and elongation of holes than anodized 6061 or anodized 2024. You can also "Young's modulus" all you want, but there's a reason why high stress aircraft parts are made from 7075 instead 6061 and there is a reason why some parts must be forged or extruded instead of cast, machined from a billet or bent
Regarding the anodized coating of 7075 versus 6061, I'll buy "some harder" or even "considerably harder" but I have a hard time with "much harder". I need to see some numbers there. You raise the issue of stress, I was addressing stiffness which is a different issue which is characterized by the Young's modulus. I have no basis for an opinion on the longevity of a 7075 forged receiver versus a 6061 machined receiver. I find it very plausible that a 7075 receiver will outlast 6061 by a good margin.
Clobbersauras
11-16-11, 17:58
Interesting posts guys. Thank you for taking the time to post your thoughts.
For the record, the position of the manufacturer is that 7075 makes superior forgings, but that 6061-T6 makes better milled parts.
Additionally, receiver walls are thicker on their 6061 receivers than on a standard 7075 receiver.
As I have tried to keep clear, this is entirely outside my field of expertise. I will say that the manufacturer has a lengthy history of successful aerospace manufacturing including, I believe, work on the landing gear of the F18.
They are also partnered up with Troy, who has traditionally built quality parts in my view.
And, finally, the guns are warranteed for life. So either the manufacturer is shrewdly assessing the milquetoast performance demands of the average AR owner and knows that virtually nobody even takes up Vulcan on their warranty (I am assuming Vulcan warranties their guns) so they sure won't be wearing out something half decent, or they aren't worried that there will be an issue.
I guess I will just measure the ID of the pinholes and so on periodically and report back every few thousand rounds if there's anything interesting to note.
So you think due to the hardness of 7075 its a pain to mill much like its a pain to cut tile? Like it causes tiny stress fractures in the al? It makes sense that 6061 would probably stress less under the impacts of a drill bit. I guess for something like that it seems logical. Tungston wouldn't make very good recievers I suppose considering its claim to be a very tough metal. Not just because of the weight.
After researching early pre-full scale military adoption of the M-16 I came across this site:
http://retroblackrifle.com/
Among the bits and pieces of historical info that the gentleman has collected is the supposed reason that Colt switched to 7075. Supposedly the hot and wet jungle environment would/did corrode the 6061 at a high rate in the front receiver pin area. There were supposedly cases of the front "Ears" of the receivers corroding all of the way through.
It is a good read, and definitely worth digesting...
--->APB
Suwannee Tim
11-16-11, 20:28
6061 and 6065 do not stand up well to corrosion.
misanthropist
11-16-11, 20:36
So you think due to the hardness of 7075 its a pain to mill much like its a pain to cut tile? Like it causes tiny stress fractures in the al? It makes sense that 6061 would probably stress less under the impacts of a drill bit. I guess for something like that it seems logical. Tungston wouldn't make very good recievers I suppose considering its claim to be a very tough metal. Not just because of the weight.
I really would not know, I am just relaying comments by the manufacturer.
I am primarily a guy who shoots guns. I don't know particularly much about what they are made of, or why.
To make the historical/developmental information easier to find I dug about and found the sight linked through the previous one I had linked to:
http://www.thegunzone.com/556dw-5.html
At the top the the page the reasons are detailed for the change of materiel.
This site is a metric TON of quality info on the developmental/political history of the 5.56.
It is basically a blow by blow of how everything came to be. The gentleman's name who put it all together is Daniel E. Watters - and he did a bang up job of it..
Clobbersauras
11-16-11, 23:35
^^thank you for those links.
I really would not know, I am just relaying comments by the manufacturer.
I am primarily a guy who shoots guns. I don't know particularly much about what they are made of, or why.
Touche salesman! I'm that way too for the most part unless I'm talking precision rigs. Substandard material and flex is your enemy in that case as tolerances are tighter. Barrel Harmonics are also pretty funky variations I don't like to think about.
misanthropist
11-18-11, 09:22
Regarding the corrosion resistance of 6061 vs 7075:
I was just pointed to an interesting test carried out by researchers at the University of Hawaii. The full paper is here:
https://www.corrdefense.org/Technical%20Papers/COMPARISON%20OF%20ACCELERATED%20CORROSION%20TESTS%20TO%20CORROSION%20PERFORMANCE%20IN%20NATURAL%20ATMOSPHERIC%20ENVIRONMENTS.pdf
They have carried out fairly thorough corrosion tests on a number of materials, including 6061-T6 and 7075-T6.
It appears to me from this testing that 6061 is in fact LESS prone to corrosion that 7075, at least in the form that it was tested.
I wonder if the issues with 6061 receivers in Vietnam were related to the fact that they were forged 6061? I am told it does not forge well.
...I wonder if the issues with 6061 receivers in Vietnam were related to the fact that they were forged 6061? I am told it does not forge well.
"Colt switches from 6061 T6 aluminum forgings to 7075 T6 aluminum forgings upon suggestion by Gene Stoner. The earlier forging were found to be prone to intergranular exfoliation in the humid climate of Vietnam. Thin areas of the receiver, such as the area around the front pivot pin hole, could completely corrode apart within as little as three months."
6061 is prone to this type of corrosion when used for forgings or extrusions
misanthropist
11-18-11, 15:49
This leads me to further wonder whether billet 6061 would have been sufficiently resistant to corrosion to make this a non-issue.
Clobbersauras
11-18-11, 19:24
After reading your link and considering the rest of the information posted in this thread, I don't disagree with your thoughts.
I think the fact that Stoner originally used 6061 somewhat minimizes the pin hole and threading concern. It wasn't until corrosion issues were experienced that the receiver material was changed. I didn't read of any other issues associated with the material other than corrosion.
misanthropist
11-18-11, 19:34
Just for the sake of ultimate clarity, I am not taking a position here...my suppositions are just that.
I do not know if my guess about billet 6061 receivers being immune to the Vietnam corrosion issue is correct. It's just a theory.
I don't work for NEA and my information has come either from just questioning them as a long-time customer or from public forums in which related questions were asked.
It's the affects on the granular structure during the forging process that makes 6061 susceptible to corrosion from intergranular exfoliation. A part cut from a billet still has it's normal resistance to corrosion
misanthropist
11-19-11, 02:55
That is my impression...I am beginning to think that the manufacturer of these guns has valid reasons for selecting 6061.
No doubt they do not have ready access to forgings, but have nearly unlimited access to 4 or 5 axis mills, and it's easier for them to do billet than anything else.
Maybe they actually have legitimately selected 6061 as the best material for their application after all.
That is entirely speculation on my part and I will just get one and spec it regularly to see how it holds up. A very interesting question IMO.
Suwannee Tim
11-19-11, 20:11
The most important factors in material selection is price and availability. If you can't afford material X it doesn't matter how good it is. If you can't get material X it doesn't matter how good it is. 6061 is commonly available in a large selection of shapes. In the majority of applications there are several materials that will give satisfactory, if not optimum service. This is true of AR uppers and lowers for the majority of users.
misanthropist
11-20-11, 13:50
I am sure I'm the only person still fixated on this thread but I would like to update, for the record, that the manufacturer of the guns mentioned in this thread has contacted me and advised that they do not use 4140 barrel steel, and when I went back to look for the spot I thought I saw that information, I could not find it, so I clearly got something wrong there.
They have described their barrels as "4150" to me. I apologize for getting my wires crossed and posting incorrect data.
4140 isn't a bad choice for barrels, just not quite as good as the 4150 CMV specified for the M16/M4 by the .mil. 4140 has been used for barrels with great results for many years. Matter of fact, the creme de la creme barrel for a FAL is the bullseye marked VCL140 hammer forged barrel made by Styer for the StG58. It's made of 4140
misanthropist
11-20-11, 17:23
True - a lot of .30 rifles have been built with 4140. But I incorrectly implied, because I believed, that NEA were using 4140.
And in the interest of not making the internet any dumber than it already is I thought I'd better clear that up.
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