UMP Trunnion
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Thread: UMP Trunnion

  1. #1
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    Default UMP Trunnion

    I need to ask a question, need to poll the experts. The answer seems apparent to me but you know what happens when you assume.

    So I bought an Omega UMP clone a few months ago. Cut to the chase; The barrel is loose in the trunnion, that is to say that barrel OD is smaller than the trunnion ID. Now it seems simple enough to me that the barrel and trunnion should be a tight/interference fit with the pin serving as an extra bit of security and to provide orientation. Is this correct? The pin should not be bearing ALL of the barrel load and conveying it to the receiver (frame, upper, whatever it's called on the UMP)?

    My Gideon Shadow has been back to Omega twice. I'm not going to assume anything yet. To be honest, I haven't taken it apart since Fedex delivered it a couple days ago. The receipt says they installed a new pin and the gun bears the same serial number, the problem probably has not been corrected.

    I've gone out of town for a couple weeks for work. when I get home I'm going to break it down and see what the story is. I'm going to ask them to replace the receiver if the barrel is still loose. Am I out of line? I'm questioning the safety of the firearm at this point.

    Forgive me for starting a separate thread. I wanted to make sure I understand the UMP design.

    Thanks
    Last edited by Dinsdale Piranha; 02-23-2020 at 03:58 PM.
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  2. #2
    Tex
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    The barrel should be a few thousandths smaller, just enough to drop in. On mine the barrel is a slip fit, in other words it will drop right in with the ejector in place. When I drive in the roll pin it's solid.
    Hope this works out for you. Mine's been a really good gun.
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    Vs asking them for a new barrel? In all likelihood they made the trunnions at the same time and will be he same ID.

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    My HDPS barrel in USC receiver is REALLY tight. So much I have to use a nylon hammer it get it seated.

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    I have a converted HK USC to UMP it's a SBR and I have the USC factory .45 barrel and a German made short UMP barrel both are very tight fitting I need a rubber mallet to tap them in/out of place, the barrel is tight even without the pin in the receiver but once pinned on that barrel is solid.

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    Thanks gents. Maybe I'll just have to live with it.

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    If you do take that pin out to inspect it, see if another barrel fits any tighter???
    Quote Originally Posted by Dinsdale Piranha View Post
    Thanks gents. Maybe I'll just have to live with it.

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    I have used 4 different German barrels as well as an HDPS barrel with my USC conversion and none of them have any play when the pin is out. The pin is absolutely needed but I don't think there should be any play without it.

  10. #9
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    IIRC the difference between my barrel OD and trunion ID is about .003" The barrel just falls out.

    I'm not going to be home for another ten days or so. I'm OoT for some training.

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    I have a Gideon Shadow that has been in to see Wade a couple times for a different reason. I never had a problem with the “play” in the barrel until he sent it back with with one of his quick barrel change push pins. I then noticed a very small amount of movement in the barrel. When using the HK barrel roll pin it had no issues/noticeable movement.

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