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    Legacy Member tj214's Avatar
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    Sten SOE/CISA Silencer Ratchet Plate Details

    Does anyone have photos or diagrams of the two "uni-directional ratchet plate" assemblies used on the SOE/CISA 22.5" suppressor? Peter's book has photos that show the right side only, and Linda Cox' scale drawing in the book shows the can only.

    This setup apparently had at least three major parts: the ratchet plate attached to the butt end of the suppressor tube, and what appears to be a two-part ratchet plate that bolted (?) to the front end of the receiver tube. In addition, apparently a spring was attached to the receiver tube fitting (or the fitting was itself made of spring steel?).

    It's obvious from the pics in Peter's book how the ratchet plate was designed and fastened to the outer suppressor tube, but the receiver fixture design is not at all clear.

    It appears these ratchet plates operated in addition to the normal ratcheting system where the barrel catch nut secured the standard barrel nut into the barrel bushing welded to the front of the receiver tube. Either that or the standard barrel catch nut teeth were ground off (which makes absolutely no sense) and the ratchet plate assemblies performed the entire job of keeping the can tight against the receiver. In short, I don't understand why these ratchet plates were necessary in addition to the normal barrel catch nut.

    I've fabbed the entire can (legal in the US with tax stamp) except for the ratchet plate assemblies and it works great as-is. Hope somebody has the necessary info so I can wrap this up!!

    I've checked all my other Sten books and innumerable websites and have come up empty.

    TIA.
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    Legacy Member tj214's Avatar
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    Not surprisingly, nobody on the site has any info. However, the MOD really came through with abundant pics, just received, in response to my request! Somebody there really went to a lot of extra effort, even taking their Mk II/S apart to take the pics. They didn't tell me who the super-troop is, so I had to send a blanket "THANK YOU!!!!" Hope it gets to the right person.

    I realize this is more than a little esoteric, but my SOE/CISA can build is complete except for the ratchet plates. As I noted in my original post, in the US it's legal to put a commercial can on a semi Sten as long as you have the tax stamp (I thought we fought a war to eliminate tax stamps, but apparently I was wrong...). So I have a B&T can for an MP5 inside my big 22.5" tube. It's amazingly quiet--almost "Hollywood silencer" quiet. Super fun to shoot. The B&T is FA rated, so if I ever get a FA Sten I'll really have a...blast!

    With the advance registration and a tax stamp I could actually build an exact duplicate of the CISA can, but it's a lot easier to put a commercial can inside a cosmetic tube--same appearance and probably about 1/8 the work (and it was still a LOT of work to get the tube done anyway).

    Anyway, the MOD provided these pics, which I'm posting in case anybody is insane enough to make an operational replica. I realize these are more of historical than practical utility, but here they are (all pics from MOD; no copyright was mentioned). The parts are definitely black, but I've lightened the images to make the detail easier to see.

    This is the portion of the ratchet assembly attached aft end of the CISA tube. The standard barrel nut is visible.:

    Attachment 111147Attachment 111148

    This is the portion attached to the front end of the Sten receiver.

    Attachment 111150Attachment 111152Attachment 111153Attachment 111149Attachment 111151

    Here is the disassembled receiver ratchet assembly.

    Attachment 111145Attachment 111146Attachment 111143Attachment 111144

    Finally, here's the drilled barrel. Peter's book gives a clear explanation of how this drilling was accomplished.

    Attachment 111154

    Now, who's up for putting this into low-rate production for the hobbyist???
    Last edited by tj214; 09-21-2020 at 06:45 PM.

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    Contributing Member RASelkirk's Avatar
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    That's a lot of holes! Does the muzzle end get a deep counterbore? Seems with that much bleed-off the bullet might not make the end of the barrel...

    Russ

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    Legacy Member tj214's Avatar
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    Peter notes it was to reduce bullet speed to subsonic, and that the CISA unit was very nearly silent from 40' (yards? can't recall) away.

    Yes...that's a lot of holes. I assume the drill press operator got intense psychological counseling after completing each barrel.

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    Legacy Member Brit plumber's Avatar
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    It’s unusual for the MOD to undertake such requests, or to have access to the material. Was it the SASC you contacted? Although part of the MOD, they are more likely to be helpful than higher level direct MOD.

    The need for the extra ratchet locking mechanism is simple. The original locking mechanism is adequate for the standard shroud and barrel but was to feeble for the extra dimensions and weight of the suppressor. The increased surface area of the additional ratchet made for a much more secure attachment.

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    Legacy Member tj214's Avatar
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    I submitted my request near the beginning of this year through a MOD website, but can't recall which URL; in fact I submitted several places and can't tell which inquiry resulted in the response. I think it was probably related to the Army small arms museum, but I got so many response emails from different URLs that I can't be sure. I looked at the source of the SOE/CISA pics in Peter's book and followed a fairly long trail from there. I know the final response came from an organization called "sercoservicedesk."

    You're right about the need for an additional closure for the big silencer (we'd call it a "suppressor" in the US, but Peter notes it was called a "silencer" during the war). My build, which so far does not include a second closure, has a tendency to work loose if the big tube is held wrong during firing. I have to be careful when I let other guys shoot it; I check barrel nut tightness after every shot or two. I also filed the teeth in the barrel nut catch a little deeper to help it better grip the barrel nut.

    From looking at the pics and showing them to several machinist friends it appears fabricating a similar unit on non-CNC equipment would be quite a difficult project. I'm toying with the idea of having the locking unit drawn up in 3D CAD and printed in one of the new 3D aerospace printing substances. Expensive as hell, so probably won't, but nice to dream about.

    Childhood fantasies tend to be expensive when actualized...but the mod looks cool and shoots like a dream. And I have the only one like it any time I to go a range.

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    Legacy Member Brit plumber's Avatar
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    Yeah it sounds like the SASC collection at Warminster (which is where some of Peters photos will have been taken as he was there).

    SERCO are a civilian contractor with fingers in many military pies. From cleaning to enquiries. They will have filtered it on to someone/somewhere they think the question is best answered. And it looks like the system actually worked!

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    Legacy Member tj214's Avatar
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    Just now received a "case resolved" email from the MOD system and the actual respondent organization that did all this exceptionally fine work is listed as "Courses - Tech School, Marlborough Hall." One wonders whether a volunteer at that organization took all the time required for this as typically a solder or government civilian would have far more important work. In any case, I'm amazed and very thankful they went to all this trouble for such an esoteric request.

    Now to see what I can do with it...

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    Legacy Member Brit plumber's Avatar
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    I think Marlborough Hall is part of the Defence Academy at Shrivenham. I wasn’t aware they had a firearms collection but good to know. I would like to know what else they hold.

  12. #10
    Legacy Member tj214's Avatar
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    Possibly limited interest because it's a replica, but I gave myself a Christmas present. Bit the bullet and fabricated the ratchet plate assembly to fit on the replica CISA tube I fabricated last year.

    I'm pretty pleased with the results. The project is about 98% cosmetically accurate, although as noted above, my version of the CISA tube contains a legal (tax stamped) B&T 9mm can embedded in the tube rather than the original baffles assemblies. I could have manufactured all the baffles, etc., like the original, but am too lazy to do all that work. What I've done here was plenty of work as it is!

    This is the original as photographed in the Britishicon Army armament museum:

    Attachment 114126

    Attachment 114127

    This is my version. Although I have the US tax stamp for the B&T suppressor, it has a normal Sten Mk II barrel and so far I haven't felt like paying an additional tax to make this a SBR (short barrel rifle); hence the paratroop grip rather than T-stock.

    Attachment 114128

    Attachment 114129

    I made the T-handle tool to unscrew the B&T can from inside the CISA tube. The long rod is 0.34375" tool steel drill rod to use as a bore alignment rod, which you know is absolutely critical if you've ever used a can.

    Nobody sells one long enough to use in a 22.5" can, so I had to figure out something else. Drill rod worked perfectly. 9mm converts to 0.35433, but the barrel lands demand a slightly smaller diameter. My experiments show 0.34375 works perfectly with my aftermarket standard Sten Mk II barrel.

    Attachment 114130

    Attachment 114131

    These are the ratchet parts I fabricated based on my study of the MOD pics (published above). MOD did not provide dimensions, so I took measurements on my Sten receiver and used a lot of LAR analysis (Looks About Right...). Guess I was fairly accurate as everything fits same as the originals. I'm not going to overload the forum with the engineering drawings I made up, but feel free to PM me and I'll send them to you.

    Attachment 114132

    Attachment 114133

    Glad I did this, but I’ll never do it again. Luckily I have a good friend who let me use his fully equipped machine shop so fabrication was not a huge deal. For comparison I sent my drawings out for quote, but don’t ask me how much the commercial shops wanted to charge—I’ll start crying again.

    What? Oh. Sorry. They're calling me back to the looney bin--gotta go now.

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