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WoW!Buy a Norc and see how long it goes to failure then post about it on CGN, sit back and watch!
You luv 2 stir the pot eh???
Wonder if the police know about your package coming in custums?
LOL!!!
7075-t6 vs 6061-t6 in a lower receiver
- Thread starter Sgt.Begood
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You luv 2 stir the pot eh???
Wonder if the police know about your package coming in custums?
LOL!!!
Exactly. The main reason they went with 7075 was that back in the day 7075 was superior for forging. These days, with billet material, 6061 will outlast any Canadian shooting.
In fact, 6061 is more than adequate for most all firearm products. The guys running steel scope rings and bases are essentially wasting money.
Young's modulus is meaningless as far material "strength" goes, yield strength the number you look at. One of the people who tried to point that out in the thread is actually a materials engineer, btw.
The analysis also only looks at normal use and fails to consider the effects each method of processing has on the alignment of the grain structure of the material, whether or not it introduces fracture and/or stress point into the material, and what those things mean to the user in the event of catastrophic failure. Even with the same material, there are differences between a part that has been forged to shape vs. one that has been machined to shape from a billet (even a forged billet). You often don't see those differences when things are working as they should be (i.e normal firing). They show themselves when things go terribly wrong: Oh shizzle! I stuck my barrel a foot into the mud and didn't notice... KABOOM! Not a concern with a lower, but with an upper...
You're not going to see any difference under normal use, you're only going to see it if you blow your gun up in some terrible way. Engineering a product isn't about just looking at normal use (that's what amateurs do), its also about looking at every conceivable mode of failure and choosing materials and processes that minimize potential harm to the user when things go wrong, even when the cause is due to the user doing something stupid.
http://en.wikipedia.org/wiki/Failure_mode_and_effects_analysis
While that's true, it's not just a question of strength. Under a severe catastrophic failure, you're going to take all of those materials way past their yield points. Doesn't matter if its 6061 or 7075, forged or machined from billet, the material IS going to fail. And if it does, I'll take the a thinner forged 7075 upper over a thicker 7075 machined billet upper any day of the week. Even though it's weaker going by data sheet numbers.
Throttle_monkey1
CGN Ultra frequent flyer
Young's modulus only shows the amount of deflection per given load on the material within the elastic range. Most aluminums are around 70GPa, while steels are around 210 GPa, give or take a few GPa. Strength wise you're right, it's not a strength number, but it is important when designing a component and which material one should spec.
Yield strength tells us the point when the material has reached the end of its elastic range and begins to suffer from plastic deformation in tension. Since a catastrophic failure of an AR is a pretty much instantaneous single overload failure, yield strength is not the only factor to look at. Ductility and toughness are a few other material properties which come in to play.
Since on an AR the chamber pressure is contained by the bolt, barrel and barrel extension, the aluminum alloy used on the upper isn't that important as neither 7075 nor 6061 will contain a catastrophic failure. Look at the pressure during a failure. Do you think 1/8-1/4 inch of aluminum can contain it regardless of it being 6061 or 7075.
OP buy which ever upper & lower allow that's makes you happy.
Yield strength tells us the point when the material has reached the end of its elastic range and begins to suffer from plastic deformation in tension. Since a catastrophic failure of an AR is a pretty much instantaneous single overload failure, yield strength is not the only factor to look at. Ductility and toughness are a few other material properties which come in to play.
Since on an AR the chamber pressure is contained by the bolt, barrel and barrel extension, the aluminum alloy used on the upper isn't that important as neither 7075 nor 6061 will contain a catastrophic failure. Look at the pressure during a failure. Do you think 1/8-1/4 inch of aluminum can contain it regardless of it being 6061 or 7075.
OP buy which ever upper & lower allow that's makes you happy.
Actually, 6061 WILL contain a catastrophic failure. NEA has a gun that they repeatedly subjected to case head failures that ought to blow a receiver apart. It just bent instead of fracturing. They were able to bend it back and do it again several times IIRC.
Again I am not an expert on metallurgy but if you can't kill a 6061 receiver with repeated case head failures, any one of which would have shattered a 7075 receiver, I don't know what extreme conditions anyone is expecting 7075 to be necessary for.
6061 was good enough for Colt, and they only dropped it because of galvanic corrosion issues common to forged 6061. 7075 is the standard only because it forges well, not because the materials properties are more suited to the needs of the machine.
Again I am not an expert on metallurgy but if you can't kill a 6061 receiver with repeated case head failures, any one of which would have shattered a 7075 receiver, I don't know what extreme conditions anyone is expecting 7075 to be necessary for.
6061 was good enough for Colt, and they only dropped it because of galvanic corrosion issues common to forged 6061. 7075 is the standard only because it forges well, not because the materials properties are more suited to the needs of the machine.
A slight overcharged load is peanuts, it doesn't produce a severe KABOOM. Plug the barrel half way with mud, a cleaning rod, or large debris close to the chamber, and then fire a full charge load. Neither of those materials will just bend, they will split and/or fracture. The question is does the receiver just split, does it separate into a few low velocity pieces or separate into dozens of small high velocity projectiles. While this may not be a big concern for a civilian rifle that will spend it life either in a safe or on a nice clean range and will never see have this happen, it is a concern for a rifle that a soldier may pick up the rifle off of the battle field and try to fire at an advancing enemy. If it blows up, does it kill him, severely injury him, or does he walk away with minor injuries? The material choice and how it was processed will determine that.
IIRC there was a plugged barrel test, which resulted in an expanded, but not shattered, receiver. But I will have to confirm that.
Throttle_monkey1
CGN Ultra frequent flyer
I would like to see the test results and parameters of the test. If you find a link, can you post it for me?
Even with a simple over the beach test the upper on the Colt AR failed catastrophically, with fragments hitting the shooter's helmet.
If you build your upper thick enough, it could contain a failure, but this topic has devolved from the OP. he should feel comfortable buying and upper or lower in 6061 or 7075.
Even with a simple over the beach test the upper on the Colt AR failed catastrophically, with fragments hitting the shooter's helmet.
If you build your upper thick enough, it could contain a failure, but this topic has devolved from the OP. he should feel comfortable buying and upper or lower in 6061 or 7075.
It was ridiculous. Due to the "atmosphere" around here they decided not to release it. They don't share my excitement for displaying destruction I guess.
Having seen the results first hand, as well as having been prone beside my friend when his Diemaco blew apart taking his eye with it, I can say that their results were phenomenal. Showcasing damage or failures is often something that a company that makes anything is leery about. Especially when it'll likely lead to conjecture and the usual gong-show of detractors. Probably not worth it in the end.
All I can say is this.. has ANYONE here seen an AR suffer a catastrophic failure that "bent" vs fracture & spall? Pretty impressive. Especially when you have experienced the extreme opposite effects. They've subjected receivers to several blowouts that have destroyed carriers, bolts internals, mags (etc) each time. One receiver was used for MULTIPLE failures.. just hammered back into shape and BCG replaced.
Having seen the results first hand, as well as having been prone beside my friend when his Diemaco blew apart taking his eye with it, I can say that their results were phenomenal. Showcasing damage or failures is often something that a company that makes anything is leery about. Especially when it'll likely lead to conjecture and the usual gong-show of detractors. Probably not worth it in the end.
All I can say is this.. has ANYONE here seen an AR suffer a catastrophic failure that "bent" vs fracture & spall? Pretty impressive. Especially when you have experienced the extreme opposite effects. They've subjected receivers to several blowouts that have destroyed carriers, bolts internals, mags (etc) each time. One receiver was used for MULTIPLE failures.. just hammered back into shape and BCG replaced.
I find the NEA Kaboom pretty odd actually, as Dave claimed at the time the barrel extension apparently did not fail although the receivers did fail, and it would appear he hasn’t changed that stance. I am no expert but after some extensive internet research, yeah I know, I have yet to find a 7075 forged receiver fail like this. From what I could find, which was quite a lot, every instance of a 7075 receiver failing was in conjunction with the barrel extension failing.
So I could only conclude that a forged 7075 receiver is strong enough to contain a Kaboom unless the blast is so great the barrel extension fails. Bolts, carriers and mags all destroyed but NOT the receivers. In fact I would say the AR was designed to fail in this exact way, containing the blast and releasing out the mag well, typically peeling the carrier like a banana. I have seen the same peeled carrier as the NEA kaboom, but never with bulged receivers.
So, if someone would like to show me a forged 7075 receiver that has failed, but the barrel extension has remained in tact I would be very interested.
I am of the opinion that forging the receiver is important.
So I could only conclude that a forged 7075 receiver is strong enough to contain a Kaboom unless the blast is so great the barrel extension fails. Bolts, carriers and mags all destroyed but NOT the receivers. In fact I would say the AR was designed to fail in this exact way, containing the blast and releasing out the mag well, typically peeling the carrier like a banana. I have seen the same peeled carrier as the NEA kaboom, but never with bulged receivers.
So, if someone would like to show me a forged 7075 receiver that has failed, but the barrel extension has remained in tact I would be very interested.
I am of the opinion that forging the receiver is important.
Throttle_monkey1
CGN Ultra frequent flyer
Forging is important, that's why it's done. It adds strength when you align your grains properly. Dave Mcfaul- can you pm me more info on the testing and results?
I won't repost it, but am genuinely curious to see it from a scientific and engineering standpoint. It's what I do for a living, although not with firearms.
I won't repost it, but am genuinely curious to see it from a scientific and engineering standpoint. It's what I do for a living, although not with firearms.
First picture that came up on "AR Kaboom" google image search:
I don't know that the barrel extension is fine, but there's no obvious information to suggest otherwise.
Similar pic.
So I would say that while 7075 receivers MAY contain a lot of failures, they don't necessarily contain any failure short of one severe enough to blow up a barrel extension.
Sorry no, that's not something that I'd be able to provide.
Even if I could, I was not present at the time of testing an have only witnessed the end results and reviewed the procedure.. And since I'm neither an engineer nor a metallurgist my opinion would only be speculation anyways. I am of the opinion though that there would be a lot of people in the industry that would be interested in the results. 6061 seems to have an unwarranted stigma in the industry for this specific application so a lot of practical testing hasn't been done. But keep in mind that the industry standard for billet material for accessories like rails, sights, etc is 6061. And they make receivers out of plastic, so you have to decide if you honestly think its a liability based on facts or voodoo curses.
As to the other point I would be willing to bet that regardless I the material if the force is such that the barrel extension is going to fail and blow apart the receiver must also. That extension has to go somewhere and path of least resistance is out the sides.
That is actually the picture Dave first provided when he posted the NEA Kaboom. IIRC the receiver extension did fail, the crack is right at the top where the receiver split. Not sure about the second picture…
And, yes, naturally, if a barrel extension fails the receiver must fail to give way to the barrel extension… I would venture a guess that it is actually the barrel extension causing the receiver to fail in most kabooms… this is pretty much the point I was trying to make.
I know it is one hell of a statement to make, perhaps why I have not done it sooner, but you have to admit I do have a bit of a point… the 6061 billet receiver is flexing where as a 7075 forged receiver would show no signs of damage in the similar situation.
WoW!
You luv 2 stir the pot eh???
Wonder if the police know about your package coming in custums?
LOL!!!
I've been know to stir on occasion
I'm sure they know ....... doesn't bother me cauz I love having my package inspected.
Maybe that is so...to be honest I have no information on the pic and am purely going on what I can see. I would guess Dave got it the same way I did: googling.
I definitely don't disagree that you have a point - that may be the case. I'm not sure whether it is or not.
By googling "AR15 kaboom barrel extension" I did find this account:
http://www.quarterbore.com/ar15m16/ar15kaboom.html
Which appears to indicate a receiver destruction without destroying the BE, and a similar failure is seen here:
http://www.m4carbine.net/showthread.php?t=91251
After more research I have noted comments such as this one:
which imply to me that this failure is not necessarily uncommon. Locating these instances only took about a minute, so I would say they can't be THAT rare (for kabooms which are inherently uncommon to begin with).
The metal characteristics are interesting academically but ultimately a red herring. 6061 is a lower spec. It's place in the market is for the low end comercial product.
I don't see any point in going with a 6061 lower. Sure it's billet and an excellent price for billet. But so what? A forged 7075 lower is abouT $10 more. If the billet lower offered ambi or something more then I could see it. But let's face it the price difference in the long run is minimum. Unless you're trying to make a super cheap build with the cheapest ok parts you can find. Even then Norinco has that locked up.
So where does the 6061 billet lower fit? Not the cheapest, not middle or high end. Cheap go Norc with 7075 forged. Middle go Aero, Palmetto armory etc with 7075 forged and excellent finish. High end there are 7075 billet and forged with ambi featured and perfect finish.
When they first came out the $1000 North American AR was a great idea. But now it's not such a big deal. They need to adapt to stay afloat. Add ambi features for build upgrades and go 7075. If sticking with 6061 then offer the extra features. Right now I don't see where they fit in the market other than as a complete rifle package.
As the statement regarding the usual detractors has already crept into this thread, I should mention most of us are only detractors because there are flaws. Most of us followed the NEA stuff from the beginning with nothing but high hopes and support. Unfortunately the end result wasn't what was hoped for. If the product was what was expected we wouldn't be detractors we would be customers.
In all fairness the NEA AR along with Norinco helped bring down the priced of higher quality stuff in Canada. The decision to go 6061 however was penny wise and pound foolish. Marketing clearly wasn't looked at with this in mind. That as a company was short sighted.
I don't see any point in going with a 6061 lower. Sure it's billet and an excellent price for billet. But so what? A forged 7075 lower is abouT $10 more. If the billet lower offered ambi or something more then I could see it. But let's face it the price difference in the long run is minimum. Unless you're trying to make a super cheap build with the cheapest ok parts you can find. Even then Norinco has that locked up.
So where does the 6061 billet lower fit? Not the cheapest, not middle or high end. Cheap go Norc with 7075 forged. Middle go Aero, Palmetto armory etc with 7075 forged and excellent finish. High end there are 7075 billet and forged with ambi featured and perfect finish.
When they first came out the $1000 North American AR was a great idea. But now it's not such a big deal. They need to adapt to stay afloat. Add ambi features for build upgrades and go 7075. If sticking with 6061 then offer the extra features. Right now I don't see where they fit in the market other than as a complete rifle package.
As the statement regarding the usual detractors has already crept into this thread, I should mention most of us are only detractors because there are flaws. Most of us followed the NEA stuff from the beginning with nothing but high hopes and support. Unfortunately the end result wasn't what was hoped for. If the product was what was expected we wouldn't be detractors we would be customers.
In all fairness the NEA AR along with Norinco helped bring down the priced of higher quality stuff in Canada. The decision to go 6061 however was penny wise and pound foolish. Marketing clearly wasn't looked at with this in mind. That as a company was short sighted.
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