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  #11  
Old 04-23-2019, 04:00 PM
Daryl Daryl is offline
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Originally Posted by Oso Polaris View Post
Thank you. Can you clarify how reaming leave the walls irregular? I thought that Reaming creates a centered, uniform hole in the neck. Are you referring to the exterior wall remaining uneven/inconsistent, which can only be corrected by neck turning? Thanks
If a case neck wall is thicker on one side than the other, a mandrel holding the case rigidly & running a cutter around the outside, removes more material where it is thicker, less where it is thinner. Many accuracy shooters simply true up case necks by removing almost all from the overly thick side, but not all of it - almost all, leaving a minor amount of extra brass, like .0002" or less. Likely having them exactly perfect made no difference in that rifle.

If you simply run an inside reamer into the neck of the case, you will remove the same amount of brass all the way around, leaving the case neck still thicker on one side than the other.

Case necks that are thicker on one side, will hold the bullet in a different relationship to the bore, depending on where the thicker part is, each time a round is fired. Thus, outside neck turning is the only way to have concentric necks. Some brass is better than others. Lapua comes to mind, but I had some .220 Swift RP brass years ago that was almost perfect, right down to 1.2" from the case mouth, the most it was out was .001".
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Last edited by Daryl; 04-23-2019 at 04:17 PM.
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  #12  
Old 04-25-2019, 04:32 AM
Oso Polaris Oso Polaris is offline
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Originally Posted by Daryl View Post
If a case neck wall is thicker on one side than the other, a mandrel holding the case rigidly & running a cutter around the outside, removes more material where it is thicker, less where it is thinner. Many accuracy shooters simply true up case necks by removing almost all from the overly thick side, but not all of it - almost all, leaving a minor amount of extra brass, like .0002" or less. Likely having them exactly perfect made no difference in that rifle.

If you simply run an inside reamer into the neck of the case, you will remove the same amount of brass all the way around, leaving the case neck still thicker on one side than the other.

Case necks that are thicker on one side, will hold the bullet in a different relationship to the bore, depending on where the thicker part is, each time a round is fired. Thus, outside neck turning is the only way to have concentric necks. Some brass is better than others. Lapua comes to mind, but I had some .220 Swift RP brass years ago that was almost perfect, right down to 1.2" from the case mouth, the most it was out was .001".
Daryl,

Thank you for the explanation. I was planning to neck turn to reduce irregularity of wall thickness/neck tension.
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  #13  
Old 04-25-2019, 05:29 PM
Daryl Daryl is offline
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Good move.
As well, you can 'tailer' the brass to have whatever neck wall you want, to reduce expansion,sizing differences, which will extend case neck life.
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