Ok, from ASM's "Metals Handbook," 9th Edition:
7075 is more corrosion-resistant thant 2024 but worse than any other
The zinc is no help, but it's the copper that's the big problem, as it
is with 2024. However, the copper improves resistance to
So in terms of general corrosion, 7075 kind of stinks. 6061 is good
even in marine environments -- although some 5xxxx and 1100 are
Current Mil spec is 7075 - T6
The original design called for either a 6 or 7 series alloy. The 6 was
cheaper and easier to work with so that was what ended up being used.
The problem is that between corrosion and thread deformation the spec
was re-written to 7075 - T6 being the "correct" alloy to use.
I have shot both and other than knowing the alloy due to the makers you
couldn't tell any real difference. 6061 is still used by a few companies
and with the design of the AR the strength in Civilian use isn't an issue.
However if you plan on needing to depend on the rifle in real combat
where you may be using it as a club, hammer or whatever, the 7075 has
the edge with regard to wear and tear.
I have used both forgings and solid billet as a starting point.
With forgings you are limited as to what you can add/subtract.
With billet you can have fun. I machined in a solid trigger guard,
milled my logo in 3D on the side, and a few other tricks.
The only data in my ASM handbook is for anodized samples exposed to a
salt-air environment. Again, 2024 and 7075 came our worst. All others,
including 6061, did better.
There also is an anecdotal comment that anodizing does not improve the
stress-corrosion characteristics of 7075, and may make it worse.
I haven't looked recently, but that's what 0% forgings were going for
last I looked. The 30% TM ones I got for $45 in qty 5+, I think the
broached magwell is worth the $20.
One key thing is to have a lower parts kit when you start the machining
so you can test fit many of the parts as you go before you tear down
each setup. It's also helpful to have a regular factory AR for visual
sanity check reference, but you can use good pictures as well.
On the first one I did I grabbed the wrong drill and drilled the hammer
and trigger pin holes oversized. After staring at it and scratching my
head for a few minutes I re-drilled the holes a bit larger to give a
reasonable size for a bushing, grabbed a piece of brass rod, threw it in
the lathe and made a set of four bushings to bring the holes down to the
correct size. I assembled the lower with a set of anti-rotation links to
act as bushing retainers and all works perfectly, you can hardly even
see the bushings under the AR links.
"Ed Huntress" wrote >
You're wrong Ed , I've melted and cast 7075 in my home foundry . Now what
I can't do is heat-treat and forge it at home . I'm not sure what's
involved with forging , though I'm pretty sure Al is worked cold . Might
have to carry a billet up the road and see what my neighbor can do with his
trip hammer ... Heat-treat requires some expensive precision equipment
Neither would I . I'd toss it into the pile for ZA alloy casting . Ed ,
where did you acquire your knowledge about casting and alloys ? Some of the
stuff you've posted is directly opposite what experience has taught me .
Well, you may have gotten lucky, or you may have a casting with
sub-surface porosity and segregation. The closest casting alloy to
7075 is 713.0, and it has less than half as much copper as 7075.
And a fraction of the strength. If they could cast 7075 versus using
713.0, they surely would.
But I hope you got lucky.
Mostly as Materials Editor at _American Machinist_. I had to study
basic metallurgy for a couple of years to be able to handle the tech
papers coming in from Alcoa, U.S. Steel, and so on.
I'm hardly an expert but I know the sources. I'm very curious about
what the hobbycasting group is saying that's directly opposite. Does
it concern 7075? It's notorious for having lousy corrosion resistance.
There are some 7xxxx alloys that are much better, but not 7075.
As for copper in aluminum, it makes it extremely hot-short and prone
to porosity. That's why welding 2024 is not recommended except by some
specialized techniques. It cracks like crazy, and if it happens not to
crack today, it may in a couple of weeks, as the HAZ age-hardens.
Anyway, what is opposite?
Already been done. There are a few companies that already sell stainless
I did one out of 416 just to see what it took. It will be the only one I
ever do as well. It machined very well but even when I thinned areas
down to reduce weight it's still pretty hefty. Does make the .308 a lot
nicer to shoot though. I have been tossing around the idea of making one
out of steel though. Thinking of areas like the sides of the mag well
Anyone with a mid sized mill can handle the job. If you buy some guides
you can even use a good drill press!
Id not mind having a lower someday. Though given the prices of the
upper Stuff..it would likely remain a door stop.
ARs are quasi legal here in California..but they have to be neutered
with a 10 rd mag and a bullet button etc etc
Kali semi-auto guns are supposed to have "fixed or not readily removable
magazines" So the bullet button was born.
Instead of the normal magazine release there is a small release button
that requires the tip of a bullet or similar to depress.
Now it has "bearings".
I was examing some sort of German rifle and pretty much any sliding parts
had actual bearings, including the ends of torsion springs- they had
little metal sleeves acting as rollers. They must have had lots of spare
time to come up with all of that.
If a tool is used to remove the magazine..by California law..its not a
"detatchable magazine equiped weapon"
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The Deadly Bullet Button
Posted by Toni on September 8, 2012
Assault weapons are banned in California. However, gun manufacturers
have found a loophole that allows gun owners to easily convert a rifle
into an assault weapon. It is a feature known as a ?bullet button,?
that enables the firearm owner to use a bullet or other pointed object
to quickly detach and replace the weapon?s ammunition magazine. The
button is recessed, preventing finger manipulation. However, by the
use of something such as a bullet, or something that can depress the
recessed button, the rifle can be converted into a semi-automatic
One rifle being manufactured by Smith & Wesson is the MP150RC which
lists: a fixed magazine and bullet button, compliant for sale in
California. This weapon has a 16? barrel with a 10-round magazine clip
that conforms to California law. With the ?bullet button? allowing the
magazine to be easily detached and replaced enabling a quick reload
that California?s assault weapon law sought to ban.
The regulations banning assault weapons define a detachable magazine
as ?any ammunition feeding device that can be removed readily from the
firearm with neither disassembly of the firearm action nor use of a
tool being required.? A bullet or ammunition cartridge is considered a
tool. Magazines, or the storage areas that allow for repeat firing,
that can be removed by a normal push button in combination with
features such as a pistol grip and telescoping stock, are banned in
California. The law essentially requires magazines to be removed and
replaced with a tool, in order to slow down the process of reloading.
The sales of bullet button conversion kits in California are only part
of the problem since assault rifle manufacturers are now marketing
so-called ?California compliant? firearms with factory-installed
bullet buttons. California now has the potential to become flooded
with bullet button-equipped weapons that undermine California?s
assault weapons law.
SB 249 prohibits the manufacture, transfer, or possession of
conversion kits but does not address the growing problem of
factory-installed bullet buttons. Providing the necessary language to
prevent challenges is time consuming, therefore it has been suggested
that since regulations are allowing bullet button-equipped weapons,
the issue would be best addressed through the regulatory process.
Clearly, the bullet button/detachable magazine problem should be
fixed. For a detailed explanation of the bullet button, see the
YouTube video below.