Starting a STEN Mk V SBR in the US

[tiriaq]

The only welds that could significantly warp the casing are those on the trigger box tabs. A heat sink slug could be slipped inside the casing.

[17thairborne]

Thanks for the suggestion. I'll see if my welder friend has something to fit.

I ordered the "guts" so that I can fit the ejector tab and make sure everything fits and functions before I weld anything. When the parts arrive I'll post some photos.

[Brit plumber]

The only welds that could significantly warp the casing are those on the trigger box tabs. A heat sink slug could be slipped inside the casing.

As mentioned on the previous page, that's what the factory did, they placed a steel bar in the body and everything was jigged to the steel bar. This prevented warping and holing and dissipated the excess heat. I do have some photos somewhere.

[Brit plumber]

Attachment 51653

[Claven2]

Just to point out for the sake of history (lol), before we had these nice stencilled tube kits, and before they became prohibited in Canada a few years ago (circa 2009), we (this site) used to build partially machined tubes and sell them with our own stencils. Sold a few before the ban stick came out The ones we sold used the old SAS-3 closed-bolt pattern.

There's lots of good build info for the MkII, which is not so different from the MKV, up in the stickies from back when I and a few other site members posted the build steps with varying availability of tooling.


nice project

[tiriaq]

While I have never seen a parts set, it is my understanding that the IO system is substantially superior to either of the SAS designs. The SAS tends to squash springs, and requires tweeking and balancing spring tensions.
A comment was made about ammunition for Stens.
Original carbines require good ammunition with strong cartridge cases. A lot of the casehead is hanging out in the open air, because of the coned breech. Thinner cases can rupture. Speaking from experience, this will get your attention! I suspect that a lot of problems with early Stens was related to the Winchester ammunition that was initially available. Blown caseheads can result in a bullet stopped in the barrel; clear the stoppage and fire, and a bulged or cracked barrel results.
The reproductions currently being made in the US are closed bolt, most firing with linear hammers. This is a very different critter than the original open bolt API guns.

[Peter Laidler]

Probably off at a different angle Tiri, but thinking about your line of thought on ammo. In the classroom and in the high speed video lab, the projectile to breech block (and therefore spent case) movement ratio was consistently about 60:1. Or in simple terms, the bullet was already 5 feet from the gun before the front end/the weakest part of the case was clear of the chamber. There was no residual gas pressure remaining at this point - the breech block is now operating under inertia/momentum of course.

Now for the nerdy bit........... It's the physics teacher in me thinking out aloud......... The interesting bit now that I think about this is at WHAT distance from the 7" long muzzle (during the firing cycle of course) will a, say, 9mm Mk2z spec projectile be at before the pressure in the barrel is negligeable?

Anyone out there in forumland know this? Any of you ammo fiends...........?

Obviously, being an Armourer, there's never a gun fault, it's ALWAYS an ammo problem and it's ALWAYS the fault of the local ammo techs - or bomb jockeys as we call them - who are personally responsible. Naturally, they always seem to think otherwise

[17thairborne]

Just to point out for the sake of history (lol), before we had these nice stencilled tube kits, and before they became prohibited in Canada a few years ago (circa 2009), we (this site) used to build partially machined tubes and sell them with our own stencils. Sold a few before the ban stick came out The ones we sold used the old SAS-3 closed-bolt pattern.

There's lots of good build info for the MkII, which is not so different from the MKV, up in the stickies from back when I and a few other site members posted the build steps with varying availability of tooling.




nice project

Thanks much! I have been reading the numerous posts here and they have helped immensely. It has made the build much easier than anticipated for someone with no machining experience. Will post more pics soon

---------- Post added at 08:50 AM ---------- Previous post was at 08:46 AM ----------

While I have never seen a parts set, it is my understanding that the IO system is substantially superior to either of the SAS designs. The SAS tends to squash springs, and requires tweeking and balancing spring tensions.
A comment was made about ammunition for Stens.
Original carbines require good ammunition with strong cartridge cases. A lot of the casehead is hanging out in the open air, because of the coned breech. Thinner cases can rupture. Speaking from experience, this will get your attention! I suspect that a lot of problems with early Stens was related to the Winchester ammunition that was initially available. Blown caseheads can result in a bullet stopped in the barrel; clear the stoppage and fire, and a bulged or cracked barrel results.
The reproductions currently being made in the US are closed bolt, most firing with linear hammers. This is a very different critter than the original open bolt API guns.

I wonder if any of the workshop makers of today have encountered problems such as the one's you mentioned. I am hopeful that the ammo of today will function without problem. I have only seen good reports on the results using factory ammo in the IO kits. I believe Jason's barrels are superior to the original ones owing to the quality of steel he uses.

---------- Post added at 08:52 AM ---------- Previous post was at 08:50 AM ----------

Probably off at a different angle Tiri, but thinking about your line of thought on ammo. In the classroom and in the high speed video lab, the projectile to breech block (and therefore spent case) movement ratio was consistently about 60:1. Or in simple terms, the bullet was already 5 feet from the gun before the front end/the weakest part of the case was clear of the chamber. There was no residual gas pressure remaining at this point - the breech block is now operating under inertia/momentum of course.

Now for the nerdy bit........... It's the physics teacher in me thinking out aloud......... The interesting bit now that I think about this is at WHAT distance from the 7" long muzzle (during the firing cycle of course) will a, say, 9mm Mk2z spec projectile be at before the pressure in the barrel is negligeable?

Anyone out there in forumland know this? Any of you ammo fiends...........?

Obviously, being an Armourer, there's never a gun fault, it's ALWAYS an ammo problem and it's ALWAYS the fault of the local ammo techs - or bomb jockeys as we call them - who are personally responsible. Naturally, they always seem to think otherwise

Peter, Keep the nerdy stuff coming, we are all learning. Wish I had listened in physics class.

[tiriaq]

Because of the coned barrel breech, the back end of the case is unsupported. With some makes of cartridge cases, the case walls in the unsupported area are pretty thin. Cases are ejected looking like little belted magnums, or occasionally rupture. Section cases, and you will see a difference with different manufacturers. Placing sectioned cases in a barrel is interesting. I first observed the "belted" and blown cases with NWM manufacture 9mm ball.

Sectionned the chamber of a SAL (Long Branch) Mk. II barrel. Sectionned several 9mm cases of different makes. Slipped them into the chamber using a breechblock so all were seated to the same depth, and took photos of them. The difference in web thickness relative to the coned breech is quite noticeable. With some cases, there isn't a whole lot of unsupported brass to contain the pressure. This was with the cases fully seated; if ignition occurs earlier in the cycle, because of advanced primer ignition, there could be even more unsupported brass when pressure spikes.
Anyone interested in seeing the photos, PM your email address, and I'll send them.

[browningautorifle]

Advance primer ignition doesn't really fire outside the chamber. In theory maybe, but the cartridge is actually fully seated and the bolt is the only thing still moving forward. That way it takes more pressure to move it back, keeping things closed longer...in theory. People picture a cartridge firing while on it's forward trip and that's just not what happens. It has to bottom out first. I know what the SAIC instructors taught us, but it just wasn't quite right...