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Thread: Crowning a chrome-lined AR15 barrel

  1. #51
    Join Date
    Sep 2008
    Location
    Central Kentucky
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    Quote Originally Posted by JCHannum View Post
    You have to go back and forth from one end to another several times to get both ends to zero out. It made sense to me to attempt to get the chamber and crown on the same centerline as the bore..
    I think I just noticed what might be the problem, (Quote) "to get the chamber and crown on the same center as the BORE."

    The chamber and the muzzle are of course fixed on their centerline with the BORE and we can't change that without bending the barrel, what we would be doing is getting the chamber and muzzle on a centerline with the AXIS! Therein lies the problem it would seem, since the bore and the rotating axis are not truly parallel due to normal bore run-out then by centering the chamber and muzzle on the AXIS we end up with the BORE running askew at the muzzle. This results in cutting the crown centered and squared with the AXIS and not the BORE, centered with the bore at the muzzle maybe but NOT squared! Obviously it's the BORE and not the rotating AXIS that we need that crown to be square with but if we center both ends then because all barrels have a less than straight bore we are doing the opposite and cutting the crown square with the axis but out of square with the bore!!!!

    By ignoring the breech center we are then free to use that end to adjust and align the gauge pin/range rod, and thus the bore at that point, to be truly parallel with the axis at the muzzle resulting in the crown also being cut truly square to the BORE.


    The bottom line is that the serious flaw to the method the 'smith tried to describe to me is that it locates any machine cuts relative to the AXIS but disregards the actual bore unless that bore happened to be perfectly straight which unfortunately none are! Now I understand what he meant when he said that by centering both ends of the barrel we are going to cut that crown square with the AXIS which is totally meaningless once the barrel is removed from the setup!
    Last edited by radkins; 01-08-2018 at 07:06 PM. Reason: To correct a typo

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