HK mig welded Mp5 trunnions exploding??? - Page 3
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Thread: HK mig welded Mp5 trunnions exploding???

  1. #21
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    Quote Originally Posted by Holescreek View Post
    While I took a break for dinner I remembered having an issue drilling a barrel pin hole in a non-drilled US made trunnion. It was the hardest thing I've ever tried to drill and ended up using carbide bits to get through it. I wonder if this is where the "through hardened" theory came from?

    Either way, here is the statement from the metallurgist taken from the original thread. Too bad his photos of the etched cross section is missing:
    Great information! Thanks for posting.

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    Ok, the gun runs fine I just don't want it to blow up in my face

    The bolt gap is between .25mm to .30mm right now, hasn't changed in 600 rounds

  3. #23
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    @Holescreek : Thanks for the great info dig!

    I'm just trying to figure how the best way to use a mig plug weld in future builds to avoid the risk of compromise trunnions

    Someone did mention running a fast wire at low amps to get less heat to avoid affecting the trunnion too much, thoughts?

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  5. #24
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    Quote Originally Posted by VX666 View Post
    @Holescreek : Thanks for the great info dig!

    I'm just trying to figure how the best way to use a mig plug weld in future builds to avoid the risk of compromise trunnions

    Someone did mention running a fast wire at low amps to get less heat to avoid affecting the trunnion too much, thoughts?
    I assume one problem will be a lot of filler bead. Which might not be so awful if you are willing to grind them down, but that won't be easy in some spots.

    I'm a bicycle guy, and some of the prettiest welds you'll ever see are unfinished TIG on high end frames. But the old Kleins and Cannondales were overwelded and then ground smooth to where you couldn't see where the tubes ended and welds started.

  6. #25
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    Quote Originally Posted by Holescreek View Post
    ...Too bad his photos of the etched cross section is missing:
    A little searching on line and I found this?. If it's not the photo your talking about I'll delete it.

    HK mig welded Mp5 trunnions exploding???-1-large-.jpg

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    Quote Originally Posted by 21HK View Post
    A little searching on line and I found this?. If it's not the photo your talking about I'll delete it.

    Click image for larger version. 

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    Good catch! That's one of them. The other was a microscopic view showing the etched surface. I've been trying to update the pictures in my MFA threads a little bit each night, it's a long process when many of them went 20 pages or more.

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    Quote Originally Posted by VX666 View Post
    @Holescreek : Thanks for the great info dig!

    I'm just trying to figure how the best way to use a mig plug weld in future builds to avoid the risk of compromise trunnions

    Someone did mention running a fast wire at low amps to get less heat to avoid affecting the trunnion too much, thoughts?
    I plug welded all my Cetme trunnions in 6 places through 1/4" holes in the receiver using a mig with .024" wire. Don't over think it. After all the research I've done nothing about welding on the trunnion worries me.

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