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Garand - McCann Adjustable Gas System questions

Discussion in 'Rifle Country' started by transalpian, Mar 9, 2009.

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  1. transalpian

    transalpian Member

    Joined:
    Aug 16, 2007
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    65
    Location:
    Jackson, OH
    Greetings!

    I just received my adjustable gas system from McCann and would like to ask for input from the forum.

    Is there a correlation somewhere between powder burn rate (and/or standard commercial ammos) and appropriate gas jet? Or is a truly trial and error process?

    What methods have you used to mark the individual gas jets? They all look pretty much the same externally, even though I know they have different size holes in them.

    I kind of expected a jet without a hole to allow for use of M2 ball. Can I simply use a hex socket cap screw without a hole?

    What else should I know?

    thanks in advance!

    'alp
     
  2. Slamfire

    Slamfire Member

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    The only correlation I can tell you is the slower the powder, the bigger the hole.

    You are not going to be able to look at a powder brand, or burn rate, then reach in your baggie and find the "proper" vent hole size. Too many varibles.

    I used my eyeball to look at the hole sizes.

    Sure. But I would still use a vented screw. As long as the rifle functions throughout the entire clip, using a vented screw is easier on the brass. This rifle, and every other gas operated mechanism, they all open up when there is a residual pressure in the chamber. In a military capacity it improves function. But it is hard on the brass. The case gets stretched during extraction.

    Leaving the vent in there adds a little dwell time, the breech pressure is a little lower on unlock, and that is easier on the brass.

    If your rifle is a rack grade, you won't notice much difference on paper. However, in a match Garand, you will be surprised how much the group is moved by vented gas plugs, and when you change the vent size, the group moves again.

    I do not recommend this as a way to shoot bullets heavier than 175 grains in the Garand. I tried shooting 190's in mine. Even though I found a vent that barely functioned the mechanism, I could tell that the heavier bullets were hard on the rifle. Accuracy was not as good as standard loaded 175's.
     
  3. transalpian

    transalpian Member

    Joined:
    Aug 16, 2007
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    Location:
    Jackson, OH
    Great feedback! Thanks!

    'alp
     
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