Aluminum AR Parts...

what exactly would you be gaining from an aluminum trigger group in the first place?.. and if youre reducing the mass of the hammer you have to significantly increase the weight of the spring

i dont think theyd last long at all, it would also result in needing a much heavier spring, couldnt be polished as smooth meaning you'll end up with a heavy, gritty, generally awful trigger pull on top of a weaker, more fragile trigger group... i think it would be a complete waste of your time

no, the hammer is also going to get slammed into the disconnector and the trigger when the bolt smacks it down to recock it, and all these components are going to be under spring tension.. figure how think the disconnector is with really no room to make it wider and them making it out of a weaker material will likely translate into snapping the claw off the disconnector if the hammer doesnt break first

Sorry for the nasty comment....

1. The sear nose and sear notch would get distorted. The trigger weight and feel would change over time.

2. The hammer spring would have to be much stronger. The trigger weight would be very high.

3. The face of the hammer would get mangled by the firing pin, and the bolt running over it.

4. The disconnector notch would not last long.

If you just want to machine something, machine a set out of steel.

Or a bolt carrier...

How long....

Less than 250 rounds I should think, regardless of tolerances held. I should think failures would start with the disconnector/hammer interface.


Todd.

OneWound said:

I like to tinker and don't mind machining them

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O-1 tool steel.

It machines nice, and can be through hardened....

The only problem is that I do not currently have the tooling to machine steel (nor the funding)

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Aluminum and steel, as well as virtually all other alloys, are machined the same way. There aren't "aluminum mills" and "steel mills". Speeds and feeds are different, but process is the same.

Now, if you're talking about using wood cutting tools, well, you're really not set up to make precision FCG parts anyway.

Having said that, aluminum FCG parts are doable, but would need steel inserts at hammer face, hammer hook, and both sear surfaces. Disconnector needs to be steel, pins need to be steel, Ti or another hard & highly abrasion resistant alloy. Selector can be 100% aluminum; I have made them from 7075-T651, saving 12 grams vs. steel:

You are correct in saying that there are not "Aluminum mills" or "Steel mills", but the tooling that we use in 3-flute tooling. This is very efficient for aluminum only (We only really work with aluminum). To use 3-flute tooling on steel would cause excessive tool wear.

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Who is "we" and what is it you're doing?

I use mostly 4 flute cutters for diamaters under 1", regardless of steel, aluminum or titanium work pieces. But you certainly can cut steel with single, 2 and 3 flute cutters, just have to calibrate speeds and feeds accordingly. Or, ya know, just buy some 4 flute carbide cutters out of pocket. If you're running CNC machines that use CAT 40 or CAT 50 , you can buy an ER32 collet adapter and and collets quite inexpensively these days (assuming such a critter isn't already in use). If you have the latitude to run programs for personal stuff, I can't imagine there'd be a problem with temporarily changing out magazine tooling.

Upper receiver, barrel nut, and receiver extension would all be nice in titanium and are low stress parts.

Lowers would be nice too, but runs into problems if you don't have an FFL and you're mass producing them.

BSW

Just as an FYI: I might be making titanium parts (we have the parts and titanium to play with for these) so what would be a cool AR part to have in titanium?

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V7 weapon systems already pretty much makes everything that can be done practically out of Ti.

http://www.vsevenweaponsystems.com/collections/frontpage

IMO, if weight savings is the goal, aluminum should be used wherever possible. Ti has an unparalleled strength to weight ratio, but still 70% heavier than Al, and obviously much more expensive, even in low grades. So, where minimum dimensions dictate that high strength Al is sufficient, it makes the most sense. Then there's Mg to consider as well.

I like Ti, like machining it, and it definitely has applications. Just generally too cost prohibitive to be used where other metals work fine. I make muzzle brakes and comps out of it, and 6/4 runs about $10 per piece just in raw materials. Aluminum or steels, including 7075-T6/T651 or 416 stainless, run under $3 per piece.

There is always aluminum lithium alloy. Lighter, stiffer, and stronger than aluminum.

No cheap, though.

BSW

Might I suggest you make some tactical pens, then use the profits to upgrade tooling as you go?

There is always aluminum lithium alloy. Lighter, stiffer, and stronger than aluminum.

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Depends on which aluminum you're talking about. The maximum lithium content by weight is a touch over 4%, and most Al-Li alloys are closer to 2% Li. The resulting alloys, such as 2099-T83, can be notably stiffer than the 2024-T351 extrusions it would replace, and so the slightly lighter alloy can also perform the same functions with dimensional reductions. In aircraft, alloys that allow 10%, 15% or greater weight reduction means a more efficient craft, hence a more profitable airplane in the fleet, so the cost is justified. With guns, not so much.

But 7000 series alloys are a whole 'nother ball game from 2000 or 6000 series that the Al-Li alloys are designed to replace. I don't believe any Al-Li alloy exceeds any property of 7075 or 7085, except corrosion resistance and weldability (7000 series is basically not weldable). Moreover, even if they did compare mechanically, the 5-10% weight savings would not justify the 4x or more material cost increase, especially when Mg alloys are strong enough and can reduce the weight by >30% with a fairly negligible cost increase.

A metallurgist could better break down the cost/benefit analysis, but for a guy who just works with a lot of different aluminum alloys, I can tell you that 7075 is most common in firearms for many reasons, namely very high strength-to-weight, moderate cost, and excellent machinability. And that is unlikely to change any time in the near future. It is my go-to for most mechanical parts that don't need the strength, hardness or abrasion resistance of high carbon steels or high grade Ti alloys.

briansmithwins said:

There is always aluminum lithium alloy. Lighter, stiffer, and stronger than aluminum.

No cheap, though.

BSW

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The problem most lay-people have with alloys is that not all "aluminum" is the same stuff.

You don't make aircraft skin out of 7075, even though 7075 has 10% to 20% greater tensile yield strength than 2024. You don't make armored vehicles out of 7075 even though 7075 is a good bit harder and stronger than 5083. And you don't make aircraft landing gear mount frames out of 2099 even though it is stiffer than 7075.

"Better" always needs to qualified with what it is "better" than and in what respects it is superior.

In the lengths of AR parts, you are not going to be able to measure the reduction in flexing gained by 'stiffer' alloys. And, the required strength of the aluminum parts in a AR is low enough that anything stronger than 6061 is a bit of over-kill. (Most of the thing was designed to be made out of 6061 in the first place.)