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Thread: 9mm barrel blank, how far should i turn it down?

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    Gunco Member par0thead151's Avatar
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    Default 9mm barrel blank, how far should i turn it down?

    Im having a machinist help me with turning down the barrel where the bolt face interacts with it. im building a 2XTM with this barrel(the 9mm barrel blanks from weaponeer)
    im wondering what exactly i should tell him to do to the barrel. if anyone can shed some light on this i would be very grateful.
    thanks

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    Happy Camper hcpookie's Avatar
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    Not sure of the question, are you asking about the face of the chamber? I assume you mean the extractor notch? ...or the overall profile? You can get measurements from here (and my site) about the default measurements of the diameters. You obviously need the barrel to fit the parts.

    If you're talking about the extractor notch, you need to machine clearance for it during the entire rotation of the locking action. On an AKM/AK74 type of bolt, you're talking about 90 degrees from top-dead-center to about the 3 o'clock position when looking from the chamber toward the muzzle.

    On an AK-100/AK-74 style bolt, you need it to be about 180 degrees around, from about 10 o'clock to the 4 o'clock location. By my measurements that was approximately .030" deep cut. Considering this is 9mm you should not be too terribly worried if it is a little deeper, however too deep and you'll expose part of the cartridge wall.


    That is documented on my AKSU template at the bottom of this page - note this is for the short barrel AKSU, not a 16" barrel, so the overall barrel measurements probably won't work for your need. However, if you have an AK-74 style bolt, the chamber area should look like this:

    http://pookieweb.dyndns.org:61129/ak/docs/templates.htm
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    No Hope For Me 1biggun's Avatar
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    If you're talking about the extractor notch, you need to machine clearance for it during the entire rotation of the locking action.

    HMM well its a 9mm an assuming its a BLOW BACK so the bolt is not rotating at all since the lugs dont need to engage on a blow back. so really you only need a notch were the extractor would hit it on a empty chamber. it needs to be deep enough to clear it. I dont think you need to have it done by machinest I think you should do it with a dremill once you determine were the extractor will hit.

    not sure of the exact question but the extraxtor groove needs to be deep enough to allow clearance when the bolt is all the way forward on a empty chamber. the barrel od needs to be about .0015" -.00175" press fit. and the barrel to bolt end (not face) clearance should be cheacked. not sure how deep the chamber is but with a round in the barrel there has to be some clearance betewen the barrel and the bolt. this is not to be confused with extractor clearance or head space. there also might be some ramping or champering involved. Id have it turned to .00175 over the ID of your trunion press it in to the correct head space and verifying the bolt is not hitting and then install the extractor and carfully pushing it forward on a ink coverd breach let it mark were it makes contact (if at all) and then carefully dremal that area away untill it dont hit.

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    Gunco Member par0thead151's Avatar
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    Quote Originally Posted by 1biggun View Post
    HMM well its a 9mm an assuming its a BLOW BACK so the bolt is not rotating at all since the lugs dont need to engage on a blow back. so really you only need a notch were the extractor would hit it on a empty chamber. it needs to be deep enough to clear it. I dont think you need to have it done by machinest I think you should do it with a dremill once you determine were the extractor will hit.

    not sure of the exact question but the extraxtor groove needs to be deep enough to allow clearance when the bolt is all the way forward on a empty chamber. the barrel od needs to be about .0015" -.00175" press fit. and the barrel to bolt end (not face) clearance should be cheacked. not sure how deep the chamber is but with a round in the barrel there has to be some clearance betewen the barrel and the bolt. this is not to be confused with extractor clearance or head space. there also might be some ramping or champering involved. Id have it turned to .00175 over the ID of your trunion press it in to the correct head space and verifying the bolt is not hitting and then install the extractor and carfully pushing it forward on a ink coverd breach let it mark were it makes contact (if at all) and then carefully dremal that area away untill it dont hit.

    bingo, i will do the dremel method, i was just wondering if it was a bit more involved than that.
    excellent, i now have a plan on how to put the 2XTM together....

    edit: how does one check barrel to bolt end clearance ?
    Last edited by par0thead151; 12-17-2008 at 11:12 PM.

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    Gunco Regular Gunter's Avatar
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    Remove the firing pin and extractor. Install go gauge in bolt and insert into barrel. Measure the gap (if there is any) between the bolt and barrel. If no gap the the barrel needs to be trimmed a little. Too much gap and the chamber will need to be cut deeper.

    Keep in mind that this has nothing to do with headspacing a blowback 9mm. It just keeps the barrel from stopping the forward moving bolt/carrier. On the 2XTM the headspace is set with the barrel, bolt/carrier, and left side of trunnion.
    "Take time to deliberate, but when the time for action has arrived, stop thinking and go in."

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    Gunco Member par0thead151's Avatar
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    last question before i get rolling on this project...
    the barrel blank has a excess chamber depth. the base/primer side of the 9mm round is about 1/4" into the chamber, so i will need to take some material off of the end of the barrel that has the chamber. basically, stick a 9mm round in the barrel and it will swallow the whole cartridge and have a good 1/4" length to take off until the base of the cartridge will be flush with the barrel.
    i want the base of the 9mm case to be flush with the barrel correct? maybe err on the side of caution and make it a few thousandths larger than my 9m case gauge to ensure every round fits?

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    Happy Camper hcpookie's Avatar
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    Details make all the difference... wish you'd have mentioned that stuff before and saved some time.

    You're describing a chamber that is too deep - you need to indeed remove metal off of the end. You need to use your headspace NO-GO gauge to get the exact depth so that there is space between the barrel and the bolt. "How much" is usually no more than .005-.008" when doing it this way. Any more, and you'll have too short a chamber. Spark plug feeler gauges help here.
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    Gunco Member par0thead151's Avatar
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    I just put a round in the chamber and noticed that it is too deep. i should have tried that sooner.
    anyways, thanks for the into, i have a 9mm go no go set on order that should arrive any day now, so i can get everything squared away then. until those arrive i can just install the mag well and do other work to the receiver.

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    Happy Camper hcpookie's Avatar
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    Let me say that with 9mm it is probably not *critical* for the measurements like it would be for a more powerful round like .308, etc. My Suomi barrel has a pretty deep notch in it, and reports indicate that the Suomi tends to bulge the cases. This of course is a bullet hose type of setup, so if it will work for that, then you should be OK if you get it "pretty close".
    Gunco Member #10

    http://pookieweb.net


    The "original" Boltcutter Rivet Squeezers:
    http://pookieweb.net/AK/rivet/boltcutters/boltcutter.htm


    Project Pink - the Pink and Blue AK-74:
    http://pookieweb.net/pink/pink.htm

  10. #10
    Gunco Member par0thead151's Avatar
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    Quote Originally Posted by hcpookie View Post
    Let me say that with 9mm it is probably not *critical* for the measurements like it would be for a more powerful round like .308, etc. My Suomi barrel has a pretty deep notch in it, and reports indicate that the Suomi tends to bulge the cases. This of course is a bullet hose type of setup, so if it will work for that, then you should be OK if you get it "pretty close".


    would i be an idiot to not wait for the case gauges to arrive and just use a live factory round or 3(a wider sampling of different brands to ensure proper case fitting) for my initial build. i can always check with the case gauge once the barrel is in place and adjust accordingly.
    thn again i would have to press the barrel out to take the material off. maybe i should just do it right the first time...

    i plan on trying to get the cases to not bulge at all as i reload 9mm.

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