Sten full auto to semi auto bolt converter

S

Spencer

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This brilliant little gizmo welds to back of a full auto bolt for a semi auto conversion. It moves the sear catch back on bolt so the bolt catches the sear immediately after passing over mag. It elimininates the possibility of making a sten run full auto by reducing the load charge until the bolt moves past the mag but does not have enough rearward thrust to catch the sear. If low power charges are tried the bolt will either catch on the sear, or not go far enough back to strip a round from the mag.

This is a LOT ! cheaper than an sas kit, and it can be easily made here in Canada by anyone with a lathe.

Before anyone says there is nothing to stop the modified bolt being swapped for an unmodified one, it is simplicity it's self to make sure that an unmodified bolt can not be inserted into the tube.

My MKIII is already semi auto, but this should make it tamper proof.

I will do the same conversion with the MKII



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I am now waiting patiently to be told by the experts why this is useless.
 
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The bolt conversion is effective from the standpoint of preventing a runaway gun in the event of low powered loads being used. It was developed in the US years ago, in an attempt to make open bolt operation acceptable. It was rejected there, because of the ruling that no open bolt firearm would be accepted.
Whether it would be useful here is anyone's guess. The BD-38 and BD-3008 have been accepted, and they have conventional long stroke open bolt systems. This would suggest that conversions like this one are not required.
You have reported that your S-ASSIII design was approved, and this approval would, do doubt, carry over to your S-ASSII, so why bother? Has your S-ASS been FaRTed yet?
 
Umm... please define "simplicity itself". I fail to see how this bolt extension prevents a FA bolt from dropping in? Or am I missing something?

Also, I fail to see how this is any different than just welding over the original sear bent and re-milling so the bent covers the width of the bolt?
 
If a typical open bolt gun is fired with selected lower powered cartridges, the bolt will not cycle far enough to the rear for the sear to catch, and the gun will fire bursts even with a semi auto trigger mechanism. The modification will allow the sear to catch the bolt just to the rear of the magazine if the bolt is short stroking, and is intended to prevent auto fire resulting from low powered ammunition. ATF will use handloaded cartridges in efforts to get guns to fire more than one round per trigger pull, and this conversion was an attempt to prevent this. Some guns were made in the US, BATFE has rejected them. It is a dead end design in the US.
As I mentionned, SSD's guns use standard long action open bolt design, and have been accepted, so there does not appear to be any point in bothering with it here.
NavyShooter is meeting with his CFO and the senior RCMP tech. next week. I am sure he would be more than happy to discuss the S-ASSes, etc. with the tech.
 
in my case, I called the CFO and my gun appears to be accepted as having no issues and is verified by the RCMP techs - just waiting for paperwork to process through and a cert to be issued. They are SOOO SLOW.
 
It would be nice if there were a FaRTed open bolt Sten design, not just the BD-3008.
The entire semi auto conversion Spencer is referring to can be found in the files section at Yahoo group sten9mm if anyone is interested. But as far as I know, the design is unacceptable in the US, and its Canadian staus is undetermined.
 
Who needs some stupid bolt extension when all you have to do is when you make the tube not cut out the FA slot for the trip arm. Its not rocket science. Unless your idea is to keep that slot for whatever reason.
 
I sent in my pictures for review last evening, and we'll see how the meeting goes. (Looking forward to it!)

I have to remember though, I'll need to put a secure locking device on the magwell, and place it in a securely locked case when I transport it for inspection/verification.

I share the concern about the above mod, as it does not prevent the use of a proper FA bolt from simply being dropped in and used. It would require someone to build it, and submit it for consideration by the RCMP, which, based on SC's experience, could be upwards of 2 years to progress.

Spencer, is that your intent?

NS
 
So what stops someone from cutting a matching slot in the bolt to where the trip lever would ride. Cut the extension at the same time. With the bolt removed this would take what, all of about 20 seconds. You now have a full auto only gun.

I suppose that along with this modification of the extra sear catch, if one were to make a 3/4" wide tripping lever, which spanned the entire width of the bolt's sear bent, and if the wide tripping lever were fixed into the gun in such a way that it couldn't be removed for modification, then it might fly.
To prevent the easy installation of a full auto bolt, you would only have to weld a pin so it protrudes into the receiver, and then cut a corresponding slot in your bolt so it can pass the pin. But then again, in about 1 minute, a guy could grind the same slot into the bolt on a regular bolt, grind off the sear bent all together, and have a sputter gun.

Another problem with all of this, is that the entire tripping lever could be defeated by a simple piece of coat hanger between the trigger and the sear.

Besides, unless Spuncer has replaced his mk3 gun's magwell with a newly made one, then he can do whatever he wants to the internals, it's still going to qualify as a converted auto.

I guess in the end, what it will come down to is someone assembling a gun with some of these mods, going through the process, and waiting for the RCMP lab to make a determiantion. The conservatives won't be in power forever (although they should be, but anytime a party is in power too long they get cocky) and by the time the gun is approved, it could well be prohibited as a semi auto restricted. I believe Contact has a gun languishing at the lab for some time now. Ask him what his options are.
 
Tiraq,

A sten with this fitted would still have the conventional long stroke open bolt system. The function is exactly the same as the originals when used with standard type ammo.

I have heard nothing from the CFC regarding my sten, maybe I will eventually maybe I won't. The mods I have made have been accepted by the CFC and it has been verrified by the verrifier they also approved., this is why I shall not be submitting it for approval. The stumbling block seems to be that they are questioning what the reciever is.

Claven2

It's as simple of welding a couple of blobs of weld to the inside of the tube, or just welding the stock to the trigger housing. Even a rivet woiuld do the job, if they are good enough for mags they are good enough for this.

The difference is that this can not run full auto with low powered rounds, with the sear slot welded on the bolt it still can


Scarecrow,

your method will do nothing to stop a gun running full auto with low powered rounds.

Navyshooter

I will go the long route with the MKII if I have to, safe in the knowledge that they will not be able to make it go full auto and will have to return it to me eventually.
 
stencollector said:
So what stops someone from cutting a matching slot in the bolt to where the trip lever would ride. Cut the extension at the same time. With the bolt removed this would take what, all of about 20 seconds. You now have a full auto only gun.
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We could do all kinds of things to make a gun full auto, but as you have said yourself we can not do that because it is illegal.

BTW The simplest way I can think of to break the law in this regard is not to change the parts at all, just change the entire gun for a full auto one.
 
Spencer said:
Tiraq, A sten with this fitted would still have the conventional long stroke open bolt system. The function is exactly the same as the originals when used with standard type ammo.
Click to expand...

This conversion adds a new bent to the bolt for sear engagement, further to the rear than the original. The sear catches the new bent, the feed lips are just to the rear of the magazine, so that the sear will catch the bolt in the event of a short recoil, as long as an unaltered semi auto trigger mechanism is used.

The instructions for the use of the bolt extension read:
"Heat treated steel bolt extension is sliped(sic) over the rear of the bolt and welded in place - bolt sear and front of the extension is(sic) then ground off flush with the flat of the bolt. This moves bolt sear to rear of bolt extension and places bolt face just behind the magazine when in cocked position. It also eliminates the full auto relief in bolt sear."
The gun functions in traditional open bolt manner, except that the foreward stroke from cocked position is much shorter, to reduce the risk of low powered ammunition resulting in bursts. The run foreward from full blowback rearward limit is longer, of course, so bolt impact on the sear is increased. In a full auto gun, this might make no difference. In a semi, the sear is going to be hit harder, every shot. A milled sear would be a really good idea.
The only function of the extension is to attempt to prevent ammunition caused uncontrolled full auto. It does not make the gun more inherently semi auto (apart from providing a full width bent), or any harder to jigger to full auto.
 
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Actually, there is an advantage to this extension. Alter the original bolt with a full width bent, for semi only. Install the extension. This gives two bents. With normal ammunition, the gun will cycle long stroke. IF there is an underpowered round, the sear will catch the bolt on the second (new) bent, and prevent the gun from doubling.
 
tiriaq said:
This conversion adds a new bent to the bolt for sear engagement, further to the rear than the original. The sear catches the new bent, the feed lips are just to the rear of the magazine, so that the sear will catch the bolt in the event of a short recoil, as long as an unaltered semi auto trigger mechanism is used.

The instructions for the use of the bolt extension read:
"Heat treated steel bolt extension is sliped(sic) over the rear of the bolt and welded in place - bolt sear and front of the extension is(sic) then ground off flush with the flat of the bolt. This moves bolt sear to rear of bolt extension and places bolt face just behind the magazine when in cocked position. It also eliminates the full auto relief in bolt sear."
The gun functions in traditional open bolt manner, except that the foreward stroke from cocked position is much shorter, to reduce the risk of low powered ammunition resulting in bursts. The run foreward from full blowback rearward limit is longer, of course, so bolt impact on the sear is increased. In a full auto gun, this might make no difference. In a semi, the sear is going to be hit harder, every shot. A milled sear would be a really good idea.
The only function of the extension is to attempt to prevent ammunition caused uncontrolled full auto. It does not make the gun more inherently semi auto (apart from providing a full width bent), or any harder to jigger to full auto.
Click to expand...

Since you'd have to produce a brand new semi automatic receiver/magwell anyway...I'd have to think a combination of things might make a very good result.

Scarecrow's idea of not making the cut for the tripping arm to go over to auto position.
Spencer's idea of welding this piece on to the bolt to make a full width sear bent and disallow using underpowered ammo to make it short cycle.

Making it so that only this bolt can be inserted into the gun or making a weld at the back such that the bolt can't be withdrawn.

I'd have to think that combo would have a good chance.

The combination of those things should make a strong case.
 
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tiriaq said:
Actually, there is an advantage to this extension. Alter the original bolt with a full width bent, for semi only. Install the extension. This gives two bents. With normal ammunition, the gun will cycle long stroke. IF there is an underpowered round, the sear will catch the bolt on the second (new) bent, and prevent the gun from doubling.
Click to expand...


Exactly.
 
tiriaq said:
Actually, there is an advantage to this extension. Alter the original bolt with a full width bent, for semi only. Install the extension. This gives two bents. With normal ammunition, the gun will cycle long stroke. IF there is an underpowered round, the sear will catch the bolt on the second (new) bent, and prevent the gun from doubling.
Click to expand...

But won't the tripping lever trip, and the sear close, before the second bent goes over? Would you have to pull the trigger twice to effect normal firing?
 
Now what I don't know about the extension is where does the recoil spring go? If the guide spigot is blanked off the bolt, there is a real risk that the spring is going to kink and collapse. In a regular Sten, the spigot on the back of the bolt can telescope back into the recoil spring guide. With the extension on the bolt, this cannot happen. This would affect the bolt stroke. If I am correct in my interpretation of the US instructions, the main casing made is a bit longer.
This alteration was designed for US conditions, but came to a dead end, because it was rejected by BATFE. Unless I am mistaken, any US gun with this system is deemed to be a NFA firearm.
 
stencollector said:
But won't the tripping lever trip, and the sear close, before the second bent goes over? Would you have to pull the trigger twice to effect normal firing?
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When the first bent hits the trip, would the second bent be already clear of the sear? I have not seen one of these, so I am not sure of the geometry, of the exact measurements. Once the disconnector has tripped, the bolt should recock on the original bent. The second bent would only become involved if there were a short recoil.
The US system removed the original bent, of course.
The extension was developed in an attempt to get BATFE to accept open bolt, and was a failure from that standpoint. Conventional open bolt has been accepted here for a few designs, so I don't think there is any reason to pursue this design concept.
 
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