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Thread: Barrel Pin Sizing

  1. #1
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    Barrel Pin Sizing

    I am getting ready to pin the barrel on my CETME-47 build and noticed the already drilled holes on my trunnion are oversized. Is the size of the barrel pin based on the hole I drill in the barrel or on the size of the holes in the trunnion?

    My trunnion measures around .203" right now and using a 5mm (.197") pin seems like there is a lot of room for the barrel to move in there.

  2. #2
    holescreek's Avatar
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    You need to keep the hole consistent in size all the way through and use a large enough pin so there is absolutely zero movement between the barrel and the trunnion. Any movement will wallow out the groove through the sift barrel material and it will start pushing forward a little every time the bolt is sent home.

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    How much of an interference fit should I be looking for? If the trunnion is .203 should I go with a .2035 pin or a .204?

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    holescreek's Avatar
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    The trunnion is case hardened so I'd keep it close. I typically grind my own pins from dowels but ordering gauge pins from Mcmaster Carr for $4 is much easier.

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    Thank you again for the help. I was able to size the trunnion holes a bit better with the un-fluted portion of a 13/64 drill bit that measured .202" One hole was .202" the other was slightly smaller so maybe .2015". I am going to get a #7 drill bit to drill the barrel and a .202 gauge pin to use to pin the barrel. That should give a good interference fit between the barrel and trunnion.

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