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Thread: diffing in to the Crossman M4-177

  1. #1
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    diffing in to the Crossman M4-177

    found a few things I would like opinions on,

    First here is the exhaust hole in the piston stock....

    Here is the exhaust hole in the valve, the rubber o ring's ID matched the ID of the hole in the barrel support (shown above)



    I remove the o ring and find this curious metal washer between the o ring and the valve exhaust port



    The actual hole in the valve is a lot bigger withut that washer. any particular reason it is there? My limited knowledge of airguns tells me this is robbing the rifle of power. If so do I just remove it, or does the washer have some function...and thus I would need to leave the washer, drilling out the center of the washer to match the hole in the valve.

    Last I find this curious hole, just below where the valve stem sticks out of the valve....what is it for....it this to vent pressure and "de tune" the rifle?




    EDIT subject should read M4-117 not M$-117
    Last edited by pharoah007; Dec 09 2012 at 07:53 PM.

  2. #2
    Member Gippeto's Avatar
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    "Washer" will restrict the flow...also spaces out the seal....a dremel might be your friend here.

    Bleed hole in valve is common on newer manufactured Crosman pumpers. A google search for plugging bleed hole in a Crosman might turn up a result or two.

    Al

  3. #3
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    well I made a new washer out of a nylon washer I had....it eas a bit to big, but I sanded it down. Now all I need to do is sand it a bit thinner (same width as the original)



    Fits real good :)


  4. #4
    Senior Member SeanMP's Avatar
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    I would check the height of the seal stack. Ideally the breach sockets into the hole in the valve. If your stack is too high you'll have trouble getting everything back together and there is a good chance the seal will blowout on the exposed edge.
    Sean

  5. #5
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    everything is back together with the new washer (washer size same in thickness and O.D. as original)

    I thought the breech would socket into the hole in the valve as well, however, upon inspecting the stock o-ring..there is no way the o rings I.D. will fit around the O.D. of the breach.

    the breach just sits in top of the gasket (sandwich fit). This is one of the reasons I want to be sure the new nylon washer was the same thickness. I actually left it a BIT thicker as to get more pressure in the "sandwich" between the o-ring and the breach.

  6. #6
    Senior Member SeanMP's Avatar
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    Sorry about the confusion. I meant a sandwich stack but with the lug on the breach just entering the hole on the valve so that the entire stack is captured within the confines of the hole

    In your first picture it looks like the oring is just proud of the valve and thus the lug is sitting above the socket hole.

    In my experience of rebuilding crosman rifles of this type the lug normally just enters the socket....However, it may not be so in this version
    Sean

  7. #7
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    well, the stock washer may just have to go back in. I do not have a "how-fast-a-ma-jig", but WOW the M4-117 is running HOT

    All I have to go by is impact signatures in my targets from before and after mod, and the sound the round makes when it hits the target. Noticeable change.

    I may have to put the washer back in as this "configuration" of rifle would be restricted if shooting over 500fps due to its appearance.

    Super pleased with the rifle tho, accuracy is real nice and with no kick at all it is real easy to shoot like you know what you know how to ;)

  8. #8
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    Thanks for the pics!
    I agree this is a great lil carbine for plinking in the backyard. I do want to mention that this rifle would NOT be restricted if made to go over 500fps as it is not a handgun. its a ten pump airgun lol

  9. #9
    Administrator AirGunEric's Avatar
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    It is, by the CFC's determination, a "Restricted" product (due to it's appearance)- you can certainly take it up with them, but let's not start telling people things that could get them in serious legal trouble. The AR-15 is not a 'handgun' either- but it's also "Restricted", as are many assault-rifle appearing products.
    I'd say I care- but I'd probably be lying...


  10. #10
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    yeah, fair enough, my bad.

    Guess its so nonsensical that it gets me mad is all...

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