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Discussion Starter #1
Hello I had been researching HK G-3 builds for about three years now. I purchased parts about a year ago. Tried to proceed, had issues and got discouraged.
Now I am back at it and thoroughly discouraged. By the way I have completed a vz-58 build and five AK platform builds and pressed barrels into all of them with ease.
A few questions I have-
1- I cannot for the life of me find whether the bolt gap is stated in mm or imperial in from people's posts. People say "oh yeah shoot for .020 or .015 doesn't make a damn sense if its in or mm.
2- The bolt carrier moves up and down after locked affecting your gap measurement by a lot. So where is it supposed to sit? pressed down? Up? in line with the cocking tube? I cannot fit any sort of feeler gauge when the cocking tube is in line with the bolt carrier no matter how far the barrel is pressed in.
20161002_144733.jpg 20161002_144743.jpg

3- The bolt gap doesn't seem to change at all no matter how far the barrel has been pressed in. I have pressed in barrel back and forth 23 times unable to figure this out.

I am ready to toss my $1600 of parts in the trash. If I cant figure this out I'm going to buy a PTR and give what I have away including a $400 match grade barrel if anyone is interested.
 

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1) The bolt gap spec is published in millimeters. People convert the numbers to inch because it's what they are familiar with and understand better. Pick one and stick with it.
2) The bolt carrier should not move up and down, it should be positively located by the receiver rails. Something is wrong.
3) The depth the barrel is pressed in has squat to do with the bolt gap. The trunnion is what determines the bolt gap for set up purposes and proper bolt gap can be obtained without a barrel even installed.

EDIT: #3 is very wrong, I have no excuses for the FUBAR. Leaving it so people know what's wrong and incorrect.
 

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Excellent advice!

1) The bolt gap spec is published in millimeters. People convert the numbers to inch because it's what they are familiar with and understand better. Pick one and stick with it.
2) The bolt carrier should not move up and down, it should be positively located by the receiver rails. Something is wrong.
3) The depth the barrel is pressed in has squat to do with the bolt gap. The trunnion is what determines the bolt gap for set up purposes and proper bolt gap can be obtained without a barrel even installed.

Your three years of research seems to have been in vain. I casually suggest you sell off your parts kit and buy that PTR and call it good.
 

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Discussion Starter #4
2- The receiver is not welded on the trunion yet, See pictures for what I am talking about
3- I thought bolt gap is what determines headspace? Headspace cant be determined without a barrel haha
 

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2) Good God, man! I don't know where to start.

3) People call it head space in roller lock weapons because it's the closest thing we understand to what's really going on. It's not head space in the traditional sense but setting bolt gap accomplishes the desired affect.

Your three years of research really didn't serve you well, did it. Believe me if you can, I'm not trying to be a smart ass when I say this, buy a PTR and call it good or send your pile of parts to someone to build for you. I'd encourage you to keep at it and keep learning but if you truly spent that long looking into the build and understand it no more than what you do, just stop. Have it built for you or buy one before you blow up $1600 (?) in parts and hurt someone or yourself.
 

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Discussion Starter #7
Is there anyone willing to give me proper advise on the bolt gap situation and how to determine how far to press the barrel?
 

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You gave him the most logical solution at this point...


2) Good God, man! I don't know where to start.

3) People call it head space in roller lock weapons because it's the closest thing we understand to what's really going on. It's not head space in the traditional sense but setting bolt gap accomplishes the desired affect.

Your three years of research really didn't serve you well, did it. Believe me if you can, I'm not trying to be a smart ass when I say this, buy a PTR and call it good or send your pile of parts to someone to build for you. I'd encourage you to keep at it and keep learning but if you truly spent that long looking into the build and understand it no more than what you do, just stop. Have it built for you or buy one before you blow up $1600 (?) in parts and hurt someone or yourself.
 

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Please disregard my comments above in their entirety.
 

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3) The depth the barrel is pressed in has squat to do with the bolt gap. The trunnion is what determines the bolt gap for set up purposes and proper bolt gap can be obtained without a barrel even installed.
Incorrect, just the opposite. The bolt-head face come to rest against the barrel causing the locking piece to push the rollers out making contact with the trunion. The farther the barrel is pressed forward, the bolt-gap shrinks.
 

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So then there is really a "headspace dimension" which would be the length from the shoulder in the cut out barrel chamber to the face of the bolt head supporting the base of the cartridge when fully closed against the barrel breech. A manufacturer would want to make sure this dimension was correct to accept standard cartridges and ensure the bolt head fully closed against the barrel breech, the rollers having the correct bolt gap at that condition?
 

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Incorrect, just the opposite. The bolt-head face come to rest against the barrel causing the locking piece to push the rollers out making contact with the trunion. The farther the barrel is pressed forward, the bolt-gap shrinks.
Thanks. I have no clue what so ever what I was thinking when I made that statement. Hence my request that my comments be ignored.
 

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So then there is really a "headspace dimension" which would be the length from the shoulder in the cut out barrel chamber to the face of the bolt head supporting the base of the cartridge when fully closed against the barrel breech. A manufacturer would want to make sure this dimension was correct to accept standard cartridges and ensure the bolt head fully closed against the barrel breech, the rollers having the correct bolt gap at that condition?
Let me see if I can answer this while keeping my foot out of my mouth.

What you describe is traditional head space measurement. In these rifles, when the bolt is closed the bolt gap has to be within specifications. Imagine the distance from the chamber shoulder to the bolt face as a constant that doesn't move, meanwhile, the bolt gap can move or be changed. The bolt gap can be changed by wear on the parts or by changing to different diameters of roller. But this only changes the gap, nothing changes the distance between the chamber internal shoulder and the bolt face. The bolt head stays put while roller size and wear changes the bolt gap.
The distance the barrel is seated needs to be in a range where the bolt gap spec can be met. No chamber gauges are used like in a traditional head space design. There is no "head space dimension" published to my knowledge, only that the bolt gap is set within specification on an empty chamber with the hammer dropped.
Again, put simply, bolt gap does not change or determine the internal distance between the bolt face and the chamber shoulder.
I hate that it's referred to so often as head space in these rifles, it only breeds confusion.
Hell, I can't even keep it right apparently.
 

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Discussion Starter #15
But gap refers to how fast or slow it will unlock that's close enough to "head space" for layman's terms. Can anyone point me in the correct direction for determining the proper gap with the barrel, bolt & carrier, and trunion? Based on that the carrier moves up and down screwing up bolt gap measurements? I have heard gap be determined by many people by just pressing barrel and testing it with the bolt carrier so someone must know...
 

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I've read somewhere here where people have pressed the barrel and set bolt gap without having the trunnion installed into the receiver but I've never seen it done. Seems to me it would cause problems like you are having, what with the carrier moving up and down. Have you tried checking the gap with the trunnion/barrel assembly and the bolt group slid into the receiver to hold everything in alignment?
 

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Discussion Starter #17
Thanks for the reply. I have not, I thought that gap was step one. That will be the next step I will try. Can anyone else confirm this is the correct method to ensuring the proper gap? From all of the threads I have read there is no mention of sliding the whole into receiver to check gap but maybe that is a given?
 

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Go over and sign up at weaponsguild, your answers are there. Admins I apologise but since he does not have pm privelidges it seems the best way to get him to the info he needs. Barrels are easier to press into the trunnion outside the platform. In a nutshell you press the barrel close to where you need it, use your bolt and carrier with the correct bolt gap feeler gauge between the bolt and carrier and finish the press. OP, go over and read the tutorial in the HK/CETME section and you should have your answers. Do not be discouraged, after folding and welding the flat pressing the barrel can be the 2nd most challenging part for a new builder of these.
 

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Discussion Starter #19
Go over and sign up at weaponsguild, your answers are there. Admins I apologise but since he does not have pm privelidges it seems the best way to get him to the info he needs. Barrels are easier to press into the trunnion outside the platform. In a nutshell you press the barrel close to where you need it, use your bolt and carrier with the correct bolt gap feeler gauge between the bolt and carrier and finish the press. OP, go over and read the tutorial in the HK/CETME section and you should have your answers. Do not be discouraged, after folding and welding the flat pressing the barrel can be the 2nd most challenging part for a new builder of these.
This guy...This guy is a hero hahaha. I will have to spend some time on this site poking around. Seems as though many people have gone through the same issues as me. Thanks very much for all the input guys!
 
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