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Old June 5, 2012, 05:01 PM   #1
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Case Length and Neck Thickness?

I know that with each loading a bottle necked rifle round gets longer and needs to be trimmed. What I didn't know is that with each loading the case neck also gets thicker. Or does it?

I read on another forum that case necks get thicker with each loading, I have never heard of this. Do they really get thicker or was this guy mistaken?
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Old June 5, 2012, 06:38 PM   #2
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When you FL size your case the brass "flows" from bottom to top. Depending upon how hard you work the brass (this might also be looked at as how well your FL die matches the dimensions of your chamber) the quality of the brass used, and the caliber, the brass will flow into the neck to a greater or lesser amount.

I have never mismatched the die and chamber so much that the brass was worked really hard, and I use Redding "S" dies and mandrels that prevent the necks from getting out of control, but I have heard of people who have had the problem you mention. In every case they were working the brass very hard.

If you have no idea of the dimensions of your chamber and/or how to set up your die to match it--if possible, you might do well to find out--if you think there is a problem. If not--why bother to fix what ain't broke?

BTW, in order to measure the thickness of your case necks, you need a tool designed for that kind of measurement. The standard calipers or micrometer will not do the job. Additionally, you have to measure each cartridge case at the same point on the neck every time, and AFTER sizing, or you may get the idea that certain necks have grown thicker, when in fact, it was just an error in measurement. For an extreme example, let's say you measure the neck thickness of a twice fired .30-06 neck at the case mouth and another at the shoulder/neck junction before sizing the case. Because the chamber is tapered from .3425" at the shoulder/neck junction to .3404" (both nominal as described in ANSI drawings) at the mouth. When the round is fired, the neck and body expands and brass flows to conform to the chamber. Measuring Od and thickness at different points of the neck will probably give different results until and unless resizing has occured. Errors in this type of measurement can also occur if expander buttons are removed from FL dies meant to resize tapered cases, since the case neck is only resized inwardly. This can also lead to the growth of the dreaded..........doughnut........

Unless these errors are allowed to become extreme, you will probably not notice any difference in performance.
"If the enemy is in range, so are you." - Infantry Journal

Last edited by amamnn; June 5, 2012 at 07:17 PM.
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