Centering Pre-Threaded Barrel Up For Chambering
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  1. #1
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    Default Centering Pre-Threaded Barrel Up For Chambering

    I've always installed bare blanks or pre-threaded and short chambered barrels. A customer brought in a pre-threaded but un-chambered carbon barrel the other day. 99% of the time i chamber through the headstock and dial in off the bore at both ends. I dialed in the blank to thread for a brake in the same fashion and after if was dialed in I measured the off of the portion of the tenon that rests under the recoil lug, its off by several thou. I'm sure the threads are off by this much also. I cant recut the threads and I would think its more important for the chamber to be spot on with the bore. I can re-cut the shoulder on the barrel after dialing in which might help. Any suggestions??

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    I’d dial in the bore than true up the shoulder. Keep it simple. Bet it will still outshoot the shooter

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    show the customer, explain the problem,
    explain the time and cost to fix the problem
    re-cut threads and shoulder, by picking up the current thread and re-cutting.

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    Quote Originally Posted by mike in co View Post
    show the customer, explain the problem,
    explain the time and cost to fix the problem
    re-cut threads and shoulder, by picking up the current thread and re-cutting.
    Why pick up the current thread if you are recutting?

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    Dial in the throat and chamber it. The shoulder was cut at the same time as the threads. Anything you do to it in a new set up is going to be less perfect.

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    Dial the bore in, leave the threads alone and make sure the cartridge has a little room in the bolt face.

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    There is a bit of play in the threads, so cutting the shoulder after dialing in the bore would help. Just my 2 cents

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    Quote Originally Posted by Mram10 View Post
    There is a bit of play in the threads, so cutting the shoulder after dialing in the bore would help. Just my 2 cents
    What will you accomplish by this?

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    Reach in and dial the bore in the neck and at the back of the chamber. Check the shoulder.

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    Quote Originally Posted by 300sniper View Post
    What will you accomplish by this?
    Verifies the shoulder is perpendicular to the bore. Should mate up square with the action face. Keeps everything square. I’m sure there are other ways, but this makes sense to me and what I’d do

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    Quote Originally Posted by Mram10 View Post
    Verifies the shoulder is perpendicular to the bore. Should mate up square with the action face. Keeps everything square. I’m sure there are other ways, but this makes sense to me and what I’d do
    What difference is that going to make over the diameter of the bolt face? How far out do you think it could possibly be?

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    If you are dialing it in on the lathe to see where it stands, it takes no time to square the shoulder. Just my humble opinion

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    And by doing that, you are taking two locating features that were absolutely perpendicular, and almost certainly making them out of square, for absolutely no gain.

    I’d be curious if anyone can claim they chambered a barrel with near zero runout in every spot from 2” in front of the throat to the breech, then completely removed it from the machine, put it back in the machine, indicated in in the same way originally done, and still found zero runout over the same length.

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    So I dial in the barrel via the bore, trim the shoulder so it is perpendicular and it will take them out of square? I disagree

    I do agree with your zero runout example though.

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    What he means is that since the barrel was threaded in a previous setup, re-cutting the shoulder in a different setup without re-threading will leave the threads and shoulder out of square.

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    Effectively, the same thing as screwing a new barrel into an untrued action.

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    Quote Originally Posted by jasonixo View Post
    What he means is that since the barrel was threaded in a previous setup, re-cutting the shoulder in a different setup without re-threading will leave the threads and shoulder out of square.
    As I posted above, there is enough slop in threads that the barrel shoulder and action face will mate without recutting threads.

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    Quote Originally Posted by wesg View Post
    Effectively, the same thing as screwing a new barrel into an untrued action.

    I assumed the action face was already trued up.

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    I'll be the odd man out on this one.
    I'd do this barrel between centers. I often do anyway, but in this case since the thread tenon is already cut I'd work off of that. No reason to assume the shoulder and threads aren't perpendicular.

    Many manufacturers want an inch cut off each end anyway,so I cut small 60 degree centers with a reamer, make a truing cut on the muzzle end, flip it around and put in the set-tru or collet(or drive it with a dog). Set the steady on the threads and chamber.

    I would't take the time to dial in through the headstock as some of the work has already been done, and the small incremental gains that may be made by painstakingly dialing in through the headstock have already been mitigated by the tenon and shoulder being cut, and a second setup won't get that back.

    As the saying goes...JMO...

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    Quote Originally Posted by tobnpr View Post
    I'll be the odd man out on this one.
    I'd do this barrel between centers. I often do anyway, but in this case since the thread tenon is already cut I'd work off of that. No reason to assume the shoulder and threads aren't perpendicular.

    Many manufacturers want an inch cut off each end anyway,so I cut small 60 degree centers with a reamer, make a truing cut on the muzzle end, flip it around and put in the set-tru or collet(or drive it with a dog). Set the steady on the threads and chamber.

    I would't take the time to dial in through the headstock as some of the work has already been done, and the small incremental gains that may be made by painstakingly dialing in through the headstock have already been mitigated by the tenon and shoulder being cut, and a second setup won't get that back.

    As the saying goes...JMO...
    I am just curious as to how you would chamber a barrel between centres?


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