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Thread: Barrel pin location challenge.

  1. #1
    drine's Avatar
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    Barrel pin location challenge.

    I removed a trunnion from an extra front stub I bought for other parts. I have my ruined Spanish barrel sitting here so I decide to see up close how these things go together.
    On my CAI CETME, the Spanish barrel pin slot was no good. About 1/8 or so short leaving the barrel face well inside the trunnion. This barrel I gaulded(see previous posts) so it slips fairly easy into a trunnion.
    So I have this newly harvested trunnion sitting here and I decide to see how close it is. Well I can't measure bolt gap obviously but lining up the slot leaves the barrel ever so slightly out of the trunnion. I'd bet it would close enough.
    The point is there must be different trunnions. I used the old piece to measue my receiver with to find the pin holes and I drilled a hole into oblivion, the hollow space between the ends.
    I can lay this trunnion next to my receiver and there is obviously differences in location.
    I see now why some folks can and have pinned using the slot provided. I guess I'm challenging the notion that the NEW BARRELS provided with kits now are slotted wrong. Maybe right for some trunnions and not for others.
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  2. #2
    Senior Veteran tomoshenko's Avatar
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    Quote Originally Posted by drine View Post
    I removed a trunnion from an extra front stub I bought for other parts. I have my ruined Spanish barrel sitting here so I decide to see up close how these things go together.
    On my CAI CETME, the Spanish barrel pin slot was no good. About 1/8 or so short leaving the barrel face well inside the trunnion. This barrel I gaulded(see previous posts) so it slips fairly easy into a trunnion.
    So I have this newly harvested trunnion sitting here and I decide to see how close it is. Well I can't measure bolt gap obviously but lining up the slot leaves the barrel ever so slightly out of the trunnion. I'd bet it would close enough.
    The point is there must be different trunnions. I used the old piece to measue my receiver with to find the pin holes and I drilled a hole into oblivion, the hollow space between the ends.
    I can lay this trunnion next to my receiver and there is obviously differences in location.
    I see now why some folks can and have pinned using the slot provided. I guess I'm challenging the notion that the NEW BARRELS provided with kits now are slotted wrong. Maybe right for some trunnions and not for others.
    Hey I LEARNT some'in on my own!
    drine,

    I read your post and it sure enforces what else I've read on the subject.
    There used to be a post with pictures that Mike put up that showed the X and Y coordinates for locating the barrel pin on an undrilled CAI receiver.
    Subsequent to that post, a builder reported that when he finally located his
    barrel pin "they weren't any where near" those posted by Mike.

    Sounds like not all trunnions are created equal...

    Is there a surefire way to acurately locate the pin? X-ray maybe, like they do on critical welds?

    I hate to think that the only way is to start doing exploratory drilling....

  3. #3
    Senior Veteran SSwee's Avatar
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    The dimensions Mike posted were from an uninstalled trunnion. The differences people get are from the differences in the receivers. The different types and manufacturers. The depths of the trunnions installed can be different from one gun to the next. I'd be willing to bet that if measurements were referenced off the trunnion instead of the receiver, the pin hole would be within a few thousandths each time.
    SS
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  4. #4
    Senior Veteran tomoshenko's Avatar
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    Quote Originally Posted by SSwee View Post
    The dimensions Mike posted were from an uninstalled trunnion. The differences people get are from the differences in the receivers. The different types and manufacturers. The depths of the trunnions installed can be different from one gun to the next. I'd be willing to bet that if measurements were referenced off the trunnion instead of the receiver, the pin hole would be within a few thousandths each time.
    SS
    Yes, but then how do you explain drines's comparison?

  5. #5
    Perro
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    the measurements i took were from a CNC mill with a mitutoyo dial indicator mounted to it to confirm true measurement.

    it was taken off of a trunnion that was not installed into a receiver.

    i know the measurement from the front of the trunnion is right - it was sloppily clamped down in a hurry to get the bottom measurement so im not 100% positive that measurement was dead nuts correct, but close enough for sure.

    ive never sat and compared trunnions - that measurement was asked for, so i took a barreled trunnion and clamped it to the table of the mill

    indexed zero to the front of the trunnion and jogged over till an end mill fit over the top of the pin good to go from eyesight. compared the reading on the computer to the dial indicator, and then posted the information.

    if there are different trunnions where pin holes are in different spots, that might explain alot of things including why someone couldnt find there pin hole off of my measurements, but ive never sat and compared a pile of trunnions to each other, so i cant say for sure

    that is why i posted all the disclaimers that it was just a guide, and could be off - your mileage may vary, etc etc

    thats why i also hate posting that information cause if your parts are different than mine and you ruin your stuff, im the Mother Fer


    Mike

  6. #6
    Senior Veteran SSwee's Avatar
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    It was my understanding that on drine's post the barrel pin groove location was what was in question. I have three bare trunnions from different sources all identical. This is not to say that there may not be some with a different design. Just for curiousities sake, here is a pic of the style I have. The diameter with the pin hole in it is approx. .462" wide with .175" straight knurl on the outer edge. This doesn't leave much room for variation in the hole positioning. Does anyone have a trunnion that is very different?
    SS
    Yo COG # 1002

  7. #7
    Senior Veteran tomoshenko's Avatar
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    Quote Originally Posted by Perro View Post
    the measurements i took were from a CNC mill with a mitutoyo dial indicator mounted to it to confirm true measurement.

    it was taken off of a trunnion that was not installed into a receiver.

    i know the measurement from the front of the trunnion is right - it was sloppily clamped down in a hurry to get the bottom measurement so im not 100% positive that measurement was dead nuts correct, but close enough for sure.

    ive never sat and compared trunnions - that measurement was asked for, so i took a barreled trunnion and clamped it to the table of the mill

    indexed zero to the front of the trunnion and jogged over till an end mill fit over the top of the pin good to go from eyesight. compared the reading on the computer to the dial indicator, and then posted the information.

    if there are different trunnions where pin holes are in different spots, that might explain alot of things including why someone couldnt find there pin hole off of my measurements, but ive never sat and compared a pile of trunnions to each other, so i cant say for sure

    that is why i posted all the disclaimers that it was just a guide, and could be off - your mileage may vary, etc etc

    thats why i also hate posting that information cause if your parts are different than mine and you ruin your stuff, im the Mother Fer


    Mike
    Mike,
    I think you have long, long, long passed from being regarded as a misinforming M-Fer!
    I know you have always qualified your posts.
    I think this discussion is geared only to rebuilding the lost body of knowledge
    on pin location and everyone is aware of the caveats...
    I didn't mean to point fingers at anyone.

  8. #8
    Ol'30 Grit jfowl31's Avatar
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    Drine, if you pressed a barrel into the bare trunnion, and were able to pin it in that spot, then you CAN measure bolt gap. It wont necessarily be all that easy, but you can do it, and just try to get it as steady as possible.

    If you have apicture of the other trunnion to compare it to SS's, maybe it could shed some light on it all.

    I guess there could have been 2 different types.... was there a different trunnion utilized for the modelo B?

    what model is the one that you stripped that trunnion from? The cocking tube has thinner lines, and the front sight isnt just plain on the modelo B...

    Ill see if I can find some up close pics of my Cetme, as its built on a Model B unissued parts kit.
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  9. #9
    Perro
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    Quote Originally Posted by jfowl31 View Post

    I guess there could have been 2 different types.... was there a different trunnion utilized for the modelo B?
    not to my knowledge - i have a complete modelo B and its the same from what i can tell

    what model is the one that you stripped that trunnion from? The cocking tube has thinner lines, and the front sight isnt just plain on the modelo B...
    the modelo B had the standard large rib cocking tube - so did the model C
    the model 1969 C cetme had the small rib cocking tube with the cast triple frame

    Ill see if I can find some up close pics of my Cetme, as its built on a Model B unissued parts kit.
    your cetme was one of the select 500 special edition ones if i recall correctly - if thats the case, those were not built on model b kits
    those were built on modelo 69C kits

  10. #10
    Ol'30 Grit jfowl31's Avatar
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    hmmmmm... I coulda sworn you told me a while back that it was a B kit... Ill take your word for it Perro. Thats all I thought I was doing before. lol.

    So whats the difference between the normal C and 69 C?
    COA #106121 COG #1000 NRA #148440199

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