Monday, July 8, 2019

A Repost - Making an AR-15 Lower From Aluminum Cans

I originally posted this article back in September of '17.  It attracted a little attention, but in the stats I can access from Google, it's not particularly popular.  Nowhere near as popular as my AR from an 80% lower series.  Recently, I went to look up the post and found the video was gone.  It didn't take long for me to find that it had been replaced by a newer, better (and slightly longer) version.  I'm redoing this post to point that out and get him more views.  The difference: YouTube Demonetized him.

There are few 20+ minute videos that I've watched that haven't had me reaching to see if I could skip over some fluff. This one had my complete attention for all 23 minutes. Guncraft101 takes five pounds of saved aluminum cans and recycles them by melting and casting an AR-15 lower.


I've got to say his PPE (personal protection equipment) made me cringe a little, but that's the only thing I can be critical of.  Upper arm-length, heavy, leather gloves combined with shorts and bare legs while pouring molten metal is enough to make me cringe.  The rest of it is great stuff to know.

That said, I have to wonder if the metal would be useful for most things.  When you see things saying they're made from "Aircraft Aluminum" or an alloy like 6061-T6 or 7075, that's a specific recipe for alloying elements in specific proportions, and T6 is a specific heat treatment.  If I took a pound of 6061-T6 cutoffs and melted those down, instead of soda cans, I wouldn't end up with 6061-T6.  All metals are like this, really.  Steel, brass, aluminum, titanium or whatever, the properties you see depend on the ingredients (alloy) and how they're treated.  Anyone who has taken the mechanical engineering classes on materials has seen something like this iron/carbon phase diagram.  The different colors code for different microstructures in the steel, the temperatures and concentrations of carbon that lead to their formations.  There are similar curves for aluminum and its main alloying additions - silicon and magnesium in 6061 or zinc and magnesium in 7075, for example.



That said, an AR-15 lower has got to be pretty non-critical.  It's not just that plastic lowers are a thing, and can be bought in any quantity from an handful of companies, there's that guy who made one at home from HDPE - the plastic used to make kitchen cutting boards (and stopped by to visit here and comment once).  If HDPE works, it's probably not a high-stress application.

I've never done casting, but I've been collecting aluminum scraps for a few years now, and have a couple of large buckets full of them (they're from 34 pound buckets of kitty litter), and I could start putting soda cans in the mix at any time.  This is climbing my list slowly. 



10 comments:

  1. Story I've heard is that cans are a deep-drawing alloy, plus the surface area is so high you lose a lot to oxide when melting. Instead, for casting use lawnmower engine blocks. To break them up into smaller pieces to fit into the crucible, put them on a wood fire until they get soft.

    Maybe one day you'll one of those NASA space probe Stirling engines, with a 30+ year lifetime because there are no seals or bearings, only small gaps and thin flexing metal supports.

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  2. I have also heard that the alloy used in aluminum cans has lackluster qualities for structural use. I agree that it's fine for a low stress part like a lower. This gentleman did an ar-10 lower from range brass, and I think it looks incredible: https://m.youtube.com/watch?v=0Z353BT6I18

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    1. That's the same guy who did this video, and he references his AR-15 casting in the AR-10 video.

      The whole time I watching, I'm thinking, "why did he cast it as solid brass instead of with openings like he did with the AR-15?" No real answer. It would be a fun project, too. He started out with 14 pounds of brass, IIRC and ended up 2lbs 2oz. I have a fair amount of brass, but I doubt I have 14 lbs. OTOH, I could cast a few pounds of brass.

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  3. Aluminum cans are made of two different alloys; the body is 3004 and the lid is 5182. Both are not heat treatable; the 3004 is alloyed with 1.2% manganese and 1% magnesium while the 5182 uses 4.5% magnesium and 0.35% manganese. They're almost opposites of each other.

    What you get when you melt cans down is going to be neither alloy.

    My buckets of chips are almost exclusively 6061, but once it's melted it loses the heat treatment (the T6 part of 6061-T6), so those become different, too.

    It's the nature of having a backyard forge. If you expect to do professional level work it takes quite a bit more effort.


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  4. A finished lower can be purchased for less than $50.00. If your time is worth nothing, to make something that is nowhere near as good as the least expensive lower, then, by all means go for it. It was an interesting experiment, but sheesh! I wouldn't do it.

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  5. And that $50 lower also is on the .GOV list of people who now own an AR-15.

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  6. The point of the exercise is to show YOU CAN.

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  7. +1 to both KurtP and Antibubba. The idea is to remind people that just like 3D printed guns, they can't stop the signal.

    There's any number of things that can make that $50 lower go away as an option - anything from the wet dream of outlawing and confiscating them, to breakdowns in the supply chain.

    Most importantly, if you don't think it's worth doing, don't do it.

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  8. I get the purpose of the video, and I apologize if I conveyed it was just about the money. This fellow showed a lot of knowledge and skill, from creating the patterns, and machining the result with the equipment he had. He showed that there is no limit to resourcefulness, hence the use of beer cans, and not a billet of 7075 or even 6061. I am sure that was part of the plan, and the real purpose of the video. Not sure if his homemade lower is as untraceable since he did put it out for the world to see, but that may be beside the point.
    More power to him and all who would do likewise.

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