Machining Question

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.

Which of 7075 and 6061 has better corrosion resistance when they are anodized?

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.

Could you machine one out of a stainless steel block?

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 though .

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 lowers.

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 for skeletonizing...

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

Gunner

What does that do to the weight???

It would center it nicely..and by the time folks get done putting all the lasers, launchers and other sundry bullshit on them...shrug...a steel lower really wouldnt be noticed too much.

Gunner

Bullet button?

Remove 333 to reply. Randy

Buy a 0% forging, make a mold from it using bondo (autobody filler) then make some machinable wax castings from that. Screw it up, just remelt the wax!

Remove 333 to reply. Randy

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.

Adds about 8 oz. to the bare lower compared to a "normal" lower.

nice save.

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"

Browse: Home / United States Takes The Gold! / Featured, News and Headlines / The Deadly Bullet Button 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 assault weapon.

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.

Laugh laugh laugh

Gunner