Sunday, July 20, 2014

The 9mm AR15 conversion

As I covered in my last post, the 9mm carbine is a nice alternative to the 5.56x45mm standard rifle round. Cost of ammunition, recoil, and noise, are all lower when you switch to 9 mm. Some ranges only let you shoot pistol calibers and will not even allow a rifle caliber on the premises.Penetration, overshoot, and backstops all have to be taken into consideration as well. Whatever your reason, the 9mm carbine just makes sense in a lot of scenarios.
I've been looking into a pistol caliber AR15 for some time, but due to the excessive cost, I've never gotten too serious about them. Just from a glance online, the prices are insane:
1. Bolt, about 200 bucks
2. Barrel, another 150-200 bucks
3. Magazine block, 50-200 bucks
4. Heavy buffer and heavier buffer spring, 50-75 bucks.
And this doesn't cover mags, or even the dedicated upper receivers.

No matter how you look at it, the cost of converting a standard AR lower to 9mm is almost the same price as an entry-level AR15. While you will eventually save that much money by shooting the inexpensive 9mm ammo, it might take you a long time.

Longtime readers of this blog will probably remember that I am
1. A cheap bastard frugal man.
2. Resourceful
As such, I felt it was time to look into caliber conversions on a budget. My ideal weapon conversion would of course, have to be inexpensive, reliable, and perhaps even adaptable to different pistol calibers, such as .45 acp, 40 S&W, and 9mm luger.
I think I have managed to put something together that will accomplish all of the above.





The magazine is from a Sten, and these mags have been used to feed 9mm, 40, and 45, so it's capable of being swapped from one upper to another.


Starting with a normal Anderson lower, I added a few parts.




A standard stripped upper, no forward assist or ejection port door are attached. They're not needed, and I will probably either machine a "featureless" upper down the road, or I'll get an Anderson upper that has no provision for a forward assist or a port door.




The barrel is a given, I started out with a "gunsmith blank" from Green Mountain Rifle Barrel. I have used dozens, if not hundreds of these barrels in different calibers, and have never had a problem with the quality.
The barrel set me back about 30 dollars, then it needed to be chambered and profiled (turned to shape on the lathe)





The "mag block" is a piece of cold roll scrap I had laying around. It takes up the remainder of the room in the magazine well, and has a release lever for keeping the mag in place.




An ejector was attached later, but here's the basic spacer block attached to the lower.



The bolt was a heavily modified Suomi bolt with a floating firing pin installed. This bolt was almost too light in this configuration, so I came up with a quick, easy, and cheap solution that uses the original buffer and recoil spring. I found some 1" round bar stock and cut a section of it to put in front of the buffer. It acts as a weight to slow bolt movement, and also shortens the stroke of the bolt by that amount. We'll see how it runs.





After slapping the gun together, I liked the way it looked with the plastic forearm and carry handle, but figured a free-floating handguard and a cheap red dot sight would look even better.


I think I was right.








The final tally of expenses revealed that I had spent well under what a normal aftermarket kit would run, and I may have actually assembled a kit that can be configured in multiple calibers.

Range report coming soon.

22 comments:

  1. Looks nice.
    It's not an SBR, right? And a can on it - is it a real silencer, or a fake extender?
    And what are you using to blue an aluminium parts?

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    1. Thank you.
      Not SBR, is 16" barrel with a fake "integral suppressor". The fake can fits over the barrel and covers it, giving the appearance of a suppressed barrel.

      That's not blued aluminum, that's matte black powder coating. See my previous post on how that's done.

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  2. I'm really having serious envy issues now. I need to take you out for a beer so I can pick your brain.

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    1. Or, perhaps a range trip? Followed by conversation over a liquid beverage?

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    2. This sounds like the beginnings of a plan. Shoot me an email via the blog, and we can fine tune some details.

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  3. Any more details on how you modified the Soumi bolt. My understanding is they are very hard steel and difficult to machine. Thank you

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    1. I have my bolts annealed before machining.
      The bolt is drilled out with a 1/4 inch bit, then I press in a sleeve for a AR15 firing pin. A slot is cut in the bottom of the bolt to allow the hammer to hit the pin.
      Also, the bolt is turned down to 1" OD and shortened slightly.

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    2. Thank you very much!! Did you have to reheat treat it afterwords?
      Thank you again!!

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    3. No, I left it annealed.
      The conditions under which it will work are not such that it needs to be hardened.

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  4. Thank you for the info!!

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    Replies
    1. You're welcome.
      Hopefully you can use it to build your own 9mm AR.

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  5. I'd really like to give it a try. It would be quite a project for me since I am pretty new to machining but maybe this winter I will give it a try. Thanks again

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  6. Have you taken it to the range and tested it yet? How well did it feed with that setup?

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    1. Yeah, I did take it to the range. It ran perfect, fed perfect. Only problem I encountered was an issue with the firing pin sleeve, I had not pinned it in place very well, and it kept the gun from popping primers after a couple mags.
      The biggest limitation in the old Sten mags is corrosion or grit, and if you clean the mags well you should not have issues with that.

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  7. Hi, very interesting indead, I was wanting to use Sterling SMG mags instaed of sten could a block be made to do this?

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    Replies
    1. I don't have any Sterling mags, but I'd imagine it could.

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  8. Wonderful article! We are linking to this great post on our site.Keep up the good writing.

    AR15 Accessories

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  9. I bought all the other parts but am about to diy my mag block. What good is a machine shop if you don't use it?

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  10. Making a mag-block is pretty straightforward, but can you provide some detail as to how you installed a catch to secure/release the Sten mag. I'd purchase one already built....if I could find it.

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    1. The mag catch is just a rocking lever that catches the pocket at the rear of the sten mag. Not a whole lot to it. Kinda like an AK mag catch.

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  11. Maybe I'm talking to myself here, but that's okay...I do it all the time. After a lengthy search, I have discovered that Hahn Precision markets the magwell blocks for Sten magazines. This device only works with the Oly 9mm upper, but that's okay since I have one. I can also help anyone convert Sten magazines to function without any magwell block at all. I wanted the block so could use unmodified Sten magazines.

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    Replies
    1. I have not seen Hahn sell those in quite some time. If you can find one and lack the ability to make one, buy it.

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