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Discussion Starter #1
Can you accurately/correctly measure the bolt gap with the trunnion and the bolt outside of the receiver? When I hold the trunnion and the bolt carrier with one hand and hold feeler gauges in the other hand, the bolt gap changes depending on how hard I am squeezing the bolt carrier and trunnion together. Is there a proper way to do this outside of a receiver?


Thanks for any help!
 

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It's difficult to get a dead nuts on bolt gap reading until the trunnion is installed in the receiver, since you can flex the carrier up/down, etc. but you can get close and try to maintain the relationship between the nose of the carrier and the barrel, so that they are as close to parallel as possible(as they will be once the cocking tube is welded up). Try to end up on the high side of the bolt gap issue (.020-ish) , and then once you have pinned the barrel and welded in the trunnion, you can adjust with larger/smaller rollers as needed.
 

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Discussion Starter #3
It's difficult to get a dead nuts on bolt gap reading until the trunnion is installed in the receiver, since you can flex the carrier up/down, etc. but you can get close and try to maintain the relationship between the nose of the carrier and the barrel, so that they are as close to parallel as possible(as they will be once the cocking tube is welded up). Try to end up on the high side of the bolt gap issue (.020-ish) , and then once you have pinned the barrel and welded in the trunnion, you can adjust with larger/smaller rollers as needed.
Thank you sir. The kit I got had a cut barrel of course but before I pressed out the pin and barrel, I used a depth mic to measure where the barrel sat in the trunnion. If I duplicate that measurement with the new barrel, am I guaranteed to be in pretty good shape with regard to head spacing?
 

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Possibly...probably...maybe. In a perfect world, yes. When I was building my CETME, Holescreek's tutorials listed a depth measurement of the barrel being around .015 proud of the trunnion breechface. I found that to be pretty much spot on. I'd aim for that, and then check your bolt gap. Holescreek is, IMHO, a Godsend to the aspiring CETME/G3/HK91 builder. He has many tutorials on MilitaryFirearm.com. Out of curiousity, what did the old barrel stub measure from the end of the trunnion? Then, of course, you'd also need to know the total depth of the trunnion from the rear surface to the breechface of it, and subtract the two. But .015 should be in the neighborhood, from rear of trunnion, to barrel face.
 

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Discussion Starter #6
Possibly...probably...maybe. In a perfect world, yes. When I was building my CETME, Holescreek's tutorials listed a depth measurement of the barrel being around .015 proud of the trunnion breechface. I found that to be pretty much spot on. I'd aim for that, and then check your bolt gap. Holescreek is, IMHO, a Godsend to the aspiring CETME/G3/HK91 builder. He has many tutorials on MilitaryFirearm.com. Out of curiousity, what did the old barrel stub measure from the end of the trunnion? Then, of course, you'd also need to know the total depth of the trunnion from the rear surface to the breechface of it, and subtract the two. But .015 should be in the neighborhood, from rear of trunnion, to barrel face.
I'll attempt to find the tutorial. Thank you sir. I measured from the opening of the trunnion to the breach and it measured 1.216". I could check and see if your measurement on my original barrel was correct with a little math.
 

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Just remember...You want your barrel to extend ABOUT .015" out from the breechface of the trunnion. If it presses in until i\the barrel is flush with the trunnion breechface, you almost CERTAINLY will have gone in too far.
 

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Discussion Starter #8
Just remember...You want your barrel to extend ABOUT .015" out from the breechface of the trunnion. If it presses in until i\the barrel is flush with the trunnion breechface, you almost CERTAINLY will have gone in too far.
I appreciate it sir. I will takes some measurements tonight to make sure your .015" and my 1.216" numbers agree with each other. Depending on how this turns out, I may be coming to you for advice on new rollers. Lol
 

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And remember...holescreek has FORGOTTEN more about building this platform than I will ever know. And I JUST realized something...I believe the numbers maybe different for a G3 than a CETME!! I apologize for the confusion. I was thinking CETME, and you're thinking G3. Go over to militaryfirearm.com and PM holescreek. He'll steer ya right. That said, I'm willing to help where/when I can. I'm following this thread.
 

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Oh, BTW...on MilitaryFirearm.com, there is a "Battle rifles" forum, and if you click on that, you'll find "CETME/HK" and "CETME/HK building resources" subforums. On the "CETME/HK" subforum, there is a thread entitled CETME &HK FAQ in the stickies. That thread has lots of good threads in it.
 

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Discussion Starter #15
The cut barrel I pushed out of the trunnion was sitting .013" proud. I pushed the new barrel in .015" proud and the bolt gap with the bolt carrier touching nothing at all will let in a .015" feeler gauge and it will not let in a .016" feeler gauge. I am not sure what the acceptable range is for the HK G3 but I feel like I am pretty close. :)
 

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Sounds like you are pretty much there, then! The two numbers match up pretty well. If you need to grow/shrink the gap from .016, you should be able to adjust via locking piece &/or rollers.
 

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BTW...It is my belief that the acceptable range is the same for both G3/CETME...that being .004-.020. Higher (.020) being preferable.
 

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Discussion Starter #18
BTW...It is my belief that the acceptable range is the same for both G3/CETME...that being .004-.020. Higher (.020) being preferable.
Awesome!!! I think I’ll live well enough alone. I really appreciate the help. I’ll leave you alone until I run into a problem pinning it. :)
 
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