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.
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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.
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 typeQuote:
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.
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.Quote:
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.
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
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
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.
My point was it is "good enough" and would last under normal use and circumstances. I understand the properties of aluminum plenty.
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.
Again, see response above.
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
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.
Completely agreeing. It can be used, but 7075 is more suitable for the job.
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
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
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.