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Magnesium!

Discussion in 'NFA Firearms and Accessories' started by MachIVshooter, Nov 9, 2018.

  1. MachIVshooter

    MachIVshooter Member

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    As I'm always wanting to try new things and have long been obsessed with the lightest possible firearms and suppressors, I decided to try a new take on my Ocelot series.

    The standard is 5.5" long and weighs 4.1 ounces, has a Ti tube, 416 SS mount & blast baffle, 7075-T651 for the other 9 baffles and front cap. Still on the lighter side of Rimfire cans, most that weigh less being almost entirely aluminum.

    IMG_2918.JPG

    I've also made monocores that are just 2.5 ounces, and my 3" long micro is 1.6 oz. But I still wanted to try something else, and I've really never worked with Magnesium before so I ordered up a length of AZ31B round stock.

    First, this stuff machines like butter! It chips like cast and cuts almost as easy as Delrin. I don't think you could hurt a tool working Mg. It produces a slightly porous but very clean finish. Mechanically, the stuff is really similar to 6061 aluminum, falling between 6061-T4 and 6061-T6 on tensile strength. Of course, the Mg is not tempered, so the base material is actually stronger. It also has a similar melting point. The big difference? Mg is 40% lighter than Al. The downside to Mg is poor corrosion resistance. AZ31B is an Al and Zn alloy, which should fare better than pure, but still will have nowhere near the corrosion resistance of anodized Al. Another concern is that it's basically anodic to everything, and the tube is Ti, which is rather noble, so any moisture in the can would be very bad. But in spite of that, I felt it worth the effort, so we have a 4" long critter with a Ti tube and Mg mount, baffles (7) and front cap:

    IMG_2919.JPG
    It sounds pretty good, not being a whole lot shorter than the standard and other rimfire cans

    IMG_2921.JPG

    I used aluminum black to get the color. I do plan to anodize the Mg, but didn't have sodium dichromate and monosodium phosphate lying around the house, so that's gonna be another day! (BTW, you should see how this stuff reacts with sufuric acid! Wow!)

    Time will tell on the durability! I'm curious, as I am not aware of anyone else having used Mg for suppressor internals. I'll keep ya'll posted!
     
    sparkyv and adcoch1 like this.
  2. LRDGCO

    LRDGCO Member

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    Isn't Magnesium ahhhh, rather highly combustible? I'm afraid that I neither enjoyed nor particularly benefited from high school chemistry. But I was a volunteer fireman, and I distinctly recall Magnesium as a very dangerous fire risk.

    So, I take it that your design, which is fascinating, if also a little above me, does not expose the Magnesium alloy to much in the way of heat?
     
  3. Havok7416
    • Contributing Member

    Havok7416 Member

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    It won't be full-auto capable I'm sure since magnesium has a low heat tolerance. I work with magnesium a bit and it seems to take damage relatively easily. Not sure I'd want to pay for a can and stamp only to beat the thing to death.
     
  4. MachIVshooter

    MachIVshooter Member

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    Magnesium will ignite in atmosphere at 880°F. Powder, small chips or thin strips are very easy to ignite, but solid masses are much more difficult. Flammability of metals like Mg, Ti and Al are a function of surface area. Think paper vs. wood block. Yes, in cases like an automobile fire where there are magnesium wheels, the wheels can get hot enough to ignite.

    The problem with Mg, Ti, Al or other lightweight alloy fires, what they were probably cautioning you about with the fire dept., is that water tends to make matters worse. Mg fire intensity increases, burning Ti can explode.

    It would be a real danger in a centerfire rifle can, which can reach that 880° pretty easily. If you manage to get a can that hot on a .22 LR, it's because you put it in a fire.

    It's hardness is really similar to 5052 al. It has a lot of similarity to 5052 mechanically, though AZ31B has more than twice the TYS of 5052-0.

    I'm not about to replace 7075-T651 parts with it, not even marketing a Mg cored can. Just wanted to give it a try and share my experiences here!
     
    Demi-human likes this.
  5. sparkyv

    sparkyv Member

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    The other problem is the extreme difficulty in putting out the Mg fire, should you actually light it off. Mg was tried in race cars skins to lighten up the overall weight, but as you can imagine it didn't turn out well for some drivers. I think still used in some wheels.

    Still...very cool MachIVshooter! You are one talented guy.
     
  6. MachIVshooter

    MachIVshooter Member

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    Yeah, basically has to be smothered completely and quickly with a retardant that won't be incinerated by the 5,000°F+ temperatures. Ti is the same way. There have been a lot of destroyed mills and lathes sent to scrap because someone let Mg or Ti chips pile up and they ignited. I've had to replace way covers from very small Ti fires myself.
     
  7. sparkyv

    sparkyv Member

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    I learned quite a bit about machining Mg and Ti from your write up, Mach.iV. Thanks!
     
  8. Elkins45

    Elkins45 Member

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    Did you buy a tube or did you turn it from solid? How’s the thread holding strength? How costly is it compared to Ti or Al?

    They made some airplane parts from Mg during WW2 to save on aluminum. I vaguely remember that the plane crash that killed some rock star was blamed on Mg parts igniting.
     
  9. Mauser lover

    Mauser lover Member

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    I seem to recall that B29 crankshafts were made of Magnesium, and they had issues due to heat until they figured out to just fly higher...

    On that note... do you know how close to that magic 880 you are getting? Just curious.
     
  10. MachIVshooter

    MachIVshooter Member

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    The tube is .030" wall titanium. Everything else is Mg. For .22 LR pressures, the Mg is plenty strong. Corrosion may be another story, though.

    Mg cost by volume is similar to gr. 5 Ti; the 1"x12" piece was $30 shipped. Not especially cheap stuff. For comparison, I pay about $7/ft for 1" 7075-T651 aluminum round bar.

    Nowhere near. It takes mag dumps on my 1,400 RPM 10/22 machine gun just to get a can uncomfortably hot to hold. I would wager that you couldn't get a can over 800°F with .22 LR short of continuous fire at M134D rates.
     
  11. Elkins45

    Elkins45 Member

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    I really need to work on my reading comprehension.
     
  12. Mauser lover

    Mauser lover Member

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    Right, but... That's the outside of the can, right? If any part of the interior of the assembly gets to 900 degrees, that could start to burn and eventually conflagrate the whole thing, right?

    I'm no physicist, but it seems to me that if you heat up a part (perhaps the wall of your first baffle, or even the inside of the wall) of your can that the heat might not dissipate fast enough to the outside of the can where it will be able to cool down (simply meaning that the inside is hotter than the outside).

    Again, not a professional physicist here, so my understanding of this is probably skewed.
     
  13. vtsteve

    vtsteve Member

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    I’m guilty of having done this myself working titanium on my very small lathe. I was quick enough to sweep the flaming mass off the bed and onto my workbench before it ruined the lathe, but as you can imagine I had to just watch it burn itself out.

    I learned a lesson about turning speeds, lubricants, and safety for sure that day. It could have gone much worse, I got lucky.
     
  14. jono

    jono Member

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    It was actually the CrankCases that were magnesium alloy and liked to burn uncontrollably...
     
    Ifishsum likes this.
  15. hso

    hso Moderator Staff Member

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