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Thread: What is the proper rest or mechanical stop for the Op Rod when in battery?

  1. #1
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    What is the proper rest or mechanical stop for the Op Rod when in battery?

    Gents, When assembling an M14 type rifle, is the OpRod's forward travel limited by resting on the gas piston? if so what constitutes the in-spec dimension & tolerance for the thickness of the gas cylinder lock, the length of the Gas piston as well as the length from the shoulder to the face for the gas plug?
    Or does the OpRod come to a stop as it bangs on to the bolt's roller with clearance between the op rod and the gas cylinder? How are these supposed to be set up?
    Thanks in advance

  2. #2
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    http://www.m14.ca/TM/026378.pdf


    not a "gent" but this may help
    "Listen With Your Eyes"
    Wit, Grit, Courage and Determination

  3. #3
    WildBillCody's Avatar
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    If you don't get an answer here by next week I have a book at home that will tell me. There is supposed to be a gap between the op rod and the gas piston.
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    Thank you Ma'am but other than table 3-3 in the TM addressing how to set up the gas cylinder it does not provide a specific answer to my query. Everything I have seen suggests a gap between the op rod and the gas piston without optimal numbers. Thanks again Ma'am.

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    looking forward to your assistance.

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    Per your thought in post 1 I'm pretty sure the functional op-rod "stop" is set by the bolt reaching lock since the op-rod handle is connected to the bolt roller. The op-rod protrusion into the gas cylinder is then set by overall op-rod length plus tolerances (small) as well as the gas cylinder location (set by the barrel shoulder).
    Recommend you refer to "The US 30Cal Service Rifles" by Jerry Kuhnhausen for part tolerances....its a great reference if you own and service your M1 & M14 (M1A) rifles. The book also provides gas system setup info & tuning for performance & accuracy. You can get it on amazon.
    Note that the gas cylinder location is changeable slightly with shims which are used to set the gas cylinder lock timing position. This is a fine adjustment for that specific purpose.

  7. #7
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    Sorry I forgot to look for it. I have to book from M1garand to M14, it has a section about NM a m14, I thought it would have something in there about fitting the gas piston/op rod. The only thing it says it the washers for the gas block should be between .018"-.021". That is to align the gas port I'm sure, it says to try different locking nuts to find one that tightens up correctly "turning to zero position with just a little force". The op rod should stop because the bolt is in battery.
    Last edited by WildBillCody; 03-20-2021 at 05:50 PM.
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    Pretty sure if the two parts are in spec (op-rod & gas piston) and that the gas cylinder is positioned (as Wild Bill noted) such that the gas port is clear then the parts "self-align" without any adjustment required. The key element is that the parts meet spec. Its a short stroke gas piston system (White system w/ self cut-off) and the gas piston "pushes" the op-rod under gas pressure.

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    Thank you for the replies; I see a gap between the gas piston and the op rod when the rifle is in battery. I have to say that I'm surprised that the bolt roller then takes the brunt of the op rod as it goes forward and it serves as the mechanical stop.

  10. #10
    WildBillCody's Avatar
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    There can't be a gap, the piston moves a good .75 if not over an inch in operation. If you have a gap, then something is wrong, does your piston move back and forth if you tip the rifle down and up?
    I love you guys...

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