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308kiwi

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About 308kiwi

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  1. 308kiwi

    Zero headspace is perfect

    To clarify what I said "head space in an AR system is measured between the front face of the barrel extension lugs and the datum point of the shoulder area of the chamber" This obviously includes the bolt, which is a fixed component that you cannot, (should not) alter.
  2. 308kiwi

    Zero headspace is perfect

    I have a very good friend who owns an engineering supply shop, I will get him on the case tomorrow
  3. 308kiwi

    Zero headspace is perfect

    Sorry dude but head space in an AR system is measured between the front face of the barrel extension lugs and the datum point of the shoulder area of the chamber, end of story. You can shift the barrel/barrel extension assembly wherever you want but it will not change this relationship.
  4. 308kiwi

    Zero headspace is perfect

    Thanks 98
  5. 308kiwi

    Zero headspace is perfect

    Alan suggested removing material from the rear of the barrel extension shoulder or the front of the receiver face, either would shift the entire assembly rearward. But yes absolutely, Fit the barrel extension, cut the chamber to head space THEN drill the gas port😀
  6. 308kiwi

    Zero headspace is perfect

    I searched for some time to find that spec to no avail, so went with 125 lb/ft and, (much to my objection because I hate the poop), high strength Loctite.
  7. 308kiwi

    Zero headspace is perfect

    All that is achieving is setting the entire barrel/barrel extension rearward, it doesn't change the relationship between the barrel extension locking lugs and the chamber, which is where you are measuring head space between. The only way to set a barrel back to remove excess head space in an AR system is to move the barrel shoulder forward by the exact amount of the thread advance, (.0625" in the case of a 308 AR), then remove the same amount from the breech face, (end of the barrel trunion), to set your bolt lug clearance then re-cut the chamber with a chamber reamer to the correct head space. And even this process is fraught with potential disaster as you would then have to torque the extension back to the barrel to the same point that it was originally installed or you would STILL end up with a gas port that wasn't at 12 o'clock. I torque extensions on both small and large frame AR's to 125 lb/ft, to achieve perfect alignment you would be tightening the extension by degrees rather than a pre-set torque limit.
  8. 308kiwi

    Zero headspace is perfect

    Sorry I don't get your point, if you set the barrel extension back?, back from where?, you are wanting to move the chamber back to reduce excess head space, the barrel extension is simply going to follow.
  9. 308kiwi

    Zero headspace is perfect

    That's not what I said, yes it would still only advance the gas port 90 degrees, BUT, the distance between each degree would be greater the further out from the axis you go, liken it to 1 MOA, 1MOA equals 1" @ 100 yards, but at 200 yards that 1" is now 2" and so on.
  10. 308kiwi

    Zero headspace is perfect

    Unfortunately not, it's the one drawback of gas operated rifles, the gas port will always move around the barrel diameter regardless of where you remove material to set the barrel back to correct excess head space. I've spent many hours trying to figure a way to do this and haven't yet come up with one that will work, except you could remove exactly .0625" from the shoulder and the breech face, this will set the chamber back .0625 and realign the gas port at 12 o'clock and then you would re-cut the chamber with a reamer to the correct head space. But to try to do this to only set the chamber/head space back a few thou doesn't work.
  11. 308kiwi

    Zero headspace is perfect

    Only problem with the method you describe is, (and I assume you are describing correcting excessive head space on an AR platform), if you remove even .005" from the shoulder of the barrel you will now have a gas port that is no longer at 12 o’clock, the thread on the DPMS style large frame extensions is 16 TPI, so for every 360 deg the thread advances .0625", .005" will rotate the gas port 2 deg, that's 2 deg is at the bore axis, the further from the axis you go, ie, to the outside diameter of the barrel the larger the 2 deg steps become, it will rapidly advance the gas port around the OD of the barrel the larger the barrel diameter. I regularly set barrels back on bolt rifles, particularly a lot of F class rifles as the owners are exceptionally pedantic about throat erosion and the process is what you describe but unfortunately it doesn't work with the AR platform.
  12. 308kiwi

    Article from 6mm BR .com AR ACCURACY

    Interesting article, thanks for sharing😎
  13. 308kiwi

    Interference fit.

    Agreed, you only need enough clearance to allow the bolt to rotate and lock, .002" - .003", any excess and the bolt lugs will end up getting hammered into the extension lugs, hard on the lugs, hard on brass, (case rims) and extractors. The last large frame AR I barrelled, in 243 Win, I set the bolt clearance @ .0005", you can almost feel the lugs moving across each other if you manually insert the bolt and rotate it in the extension 😬, but my theory being it gets cleaned enough that powder residue etc will not be a problem. It's been 100% reliable and has close to 600 rnds, suppressed, through it now.
  14. 308kiwi

    Interference fit.

    What brand of barrel extension are you using??, I've only ever used BAT Machine 308 extensions and they are to spec, (if there is such a thing), point is you will not need to modify them. Even amongst the plethora of AR15 extension manufacturers I've fitted, damn I'd couldn't even tell ya how many, barrels/extensions, to the small frame guns and have never had to alter the extension specs, and even if you did try, I'd say damn good luck to you, they are as hard as the hobs of hell, you'll need some pretty decent tooling to do so.
  15. 308kiwi

    Interference fit.

    Not sure if I am reading the OP's question/post correctly BUT................ The front face of the carrier stops against the rear face of the barrel extension, this is how it is designed to work, the bolt stops against the breech face, (rear face of the barrel), the carrier keeps moving forward camming the bolt around to lock via the cam pin and then stops against the rear face of the barrel extension. When the bolt is locked into the barrel extension there should be no clearance between the front of the carrier and the rear of the barrel extension. If you have clearance between the carrier and the barrel extension then you have a problem, in that the cam pin is now acting as the 'stop' mechanism for the entire BCG and all it's momentum when it stops in battery. The cam track in the carrier is ever so slightly longer that the length of the locking lugs in the barrel extension, this means the cam pin reaches it's most rearward travel, (when the bolt if fully cammed and locked), without reaching the end of the cam track because the carrier has come to rest against the back face of the barrel extension and the bolt lugs are sitting neatly between the front face of the extension lugs and the breechface. Have a look at any AR system that has plenty of rounds through it, you'll see a good solid witness of the front of the carrier on the rear of the barrel extension, a little extra proof that this is how it works is the phenomenon of bolt bounce on full auto M16's, carrier hits the extension with so much momentum that it bounces back, slightly unlocking the BCG, BUT on full auto the hammer has been released just before the BCG goes fully into battery, the BCG bouncing back off the extension meets the hammer as it's falling, BCG partly unlocked, firing pin is now not long enough to reach the primer, hammer hits the bottom edge of the BCG and the whole lot rides into battery, resulting in the hammer down on a live round. The only way to check what you are asking Alan Waters is to do so with an extension that has been properly fitted to a barrel and the barrel is located and secured into the upper, from the way the OP's posts read this is not what he is doing and he's seeing an issue that will go away when the rifle is assembled, (correctly), and as a whole. Some pics would help Alan Waters, trying to guess context leads to all sorts of confusion😀
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