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Thread: Suomi M31 Receiver end cap question?

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    Gunco Member Honest1's Avatar
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    Default Suomi M31 Receiver end cap question?

    I have heard about a diaphram in the end cap of an original Suomi 31 for a vacumn. Does anyone have info on this? My receiver end caps have holes on the inside as does every other kit I've heard about. Is this the extent of original equipment or is there something missing?
    Last edited by Honest1; 06-22-2009 at 06:41 PM. Reason: title not specific

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    I remember hearing something about there being a vacuum in the back of the receiver that slowed down the bolt when it went forward, probably also worked to reduce the spring needed in when the bolt went rearward too.

    They mighta had reed valves to let air out when the bolt went back, then it had to rush in through other places when it went forward. Huh, you could make it pull air in to the receiver and blow it out over the barrel, I think the italian spectre SMG does this.

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    gunco irregular moleman's Avatar
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    The end cap is composed of: the cap; a diaphram; a diaphram spring; a spring guide; and a set screw for the spring guide. The end cap does in deed release air from behind the bolt on the recoil stroke, which forms a vacuum on the return stroke to act as a rate reducer. I haven't seen a semi design that was sealed well enough IMHO to the extent where the rate reducer would form enough of a vacuum to work, and besides its a semi. I'll see If I can get a pic of the internals up later tonight.

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    Gunco Member Honest1's Avatar
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    Thanks

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    gunco irregular moleman's Avatar
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    Here's a couple pics of the endcap parts and how they fit.
    Attached Images Attached Images

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