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Old February 4, 2010, 05:31 PM   #1
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What is everyones thought on the sten guns. How hard is it to convert to semi.
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Old February 4, 2010, 05:38 PM   #2
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Can you, either practically or legally? According to the ATF...once an auto, always an auto. You probably have to build a semi-auto receiver and use the rest as a parts kit.
I'm sure someone can give you a better legality answer.
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Old February 4, 2010, 05:48 PM   #3
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I believe that the Sten is an open bolt gun - so it's going to be very difficult to make one into a legal semi-auto using a full-auto parts set. But, check this out for semi-auto sten kits:
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Old February 4, 2010, 06:56 PM   #4
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I'm not sure how attempting to convert an unregistered FA receiver into non-contraband would work.
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Old February 4, 2010, 09:30 PM   #5
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Sten MK II has a semi position on the selector button. One way is full and the other way is semi. The "safety" is pulling the cocking bolt into a cutout in the receiver tube.

It is VERY easy to fire one shot. The open bolt design is VERY slow so a single shot is very easy if you just prefer to do that.

the select fire mechanism is in the "lower group" not the "Tube". Making a "Semi-only" from a De-milled parts kit and a receiver tube would be VERY easy (Of course registering as a AOW), all you would need to do is weld the selector in the semi position making it incapable of firing full auto. It will still of course fire open bolt, like the old MAC's which would be in violation of the BATFE rules and you have the problem of the short barrell on a "Rifle" . So too many problems to deal with, just go buy yourself a titled Class III.

Last edited by 94Girl; February 5, 2010 at 11:55 AM.
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Old February 4, 2010, 10:53 PM   #6
James K
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Won't be legal. BATFE says a semi-auto can't fire from an open bolt, too easy to convert to full auto. Anyway, as pointed out, there would be no point in converting a legal machinegun to semi, since it would still legally be a machinegun. In other words, it would still be "on paper" and transfer would still require the tax. But an irreversible conversion would cut the value at least 80 percent, not a very wise thing to do.

Of course, if one should own a STEN that is not registered, it is illegal and converting it to semi cannot and will not make it legal.

Whether the STEN selector is set to semi or full, the gun still fires from an open bolt. In the semi position, the bolt moving forward trips the disconnector and releases the sear to catch the bolt when it comes back.

The STEN firing pin is machined as part of the bolt, and fires the round as the bolt closes ("open bolt firing"). BATFE says a legal semi has to have the bolt close on the loaded chamber, then have a separate firing pin that is driven by a separate part ("closed bolt firing"). That is why it is difficult to make the STEN system into a semi and the parts are expensive.

Jim K
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Old February 5, 2010, 08:37 AM   #7
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If you want to build a semi-auto only sten, it is very possible to do this. See my post above, where I pointed out a company that makes a semi-auto sten kit. Fires from a closed bolt.
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Old February 5, 2010, 08:51 AM   #8
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In shotgun news several months ago,one of the gunsmith/writers project was converting a sten kit into a semi-auto rifle.New and reduced in diameter receiver,turned down bolt,and ar-15 trigger,hammer,firing pin.
The biggest thing is to make sure that no full auto parts will fit after you're done making it into a rifle(16 inch barrel),or pistol (doing away with the ability to mount a stock) And by previous statements must be a closed bolt.
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Old February 5, 2010, 09:22 PM   #9
Willie Lowman
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The ATF doesn't say you can't make a gun that fires from an open bolt. You just have to make a gun that the butchers in the tech branch can't make full auto. That is pretty near impossible with an open bolt.
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Old February 6, 2010, 03:54 PM   #10
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My hubby is building one now for a client from a de-milled MRK III kit. It’s a very involved project but it’s going to be awesome when it’s done. I’ll post some pics tonight that we sent the client of the STEN being built. It’s a closed bolt on a new receiver tube that has a thicker wall as not to allow the insertion of a full auto bolt. The original trigger group/sear are used, but instead of the sear dropping a bolt, it drops a striker/hammer. The auto selector is modified to become the safety selector.
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Old February 7, 2010, 07:35 PM   #11
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Old May 12, 2010, 06:57 PM   #12
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Finally finished
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