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Old March 25, 2013, 10:21 AM   #1
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Measuring the case thickness of the neck?

I am having trouble getting reliable inside neck thickness measurements. I have tried calipers but placement of the caliper and tension applied have proven to give a wide variance. I am sure it is a matter of user error. To that end, I am looking for a"simpler" tool to use. Any recommendations? Micrometers or other. Forester has a tool that can measure run out, neck concentricity and neck thickness. I would prefer a digital read out if possible.


Last edited by Audioruss; March 25, 2013 at 11:08 AM. Reason: Wrong terminology
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Old March 25, 2013, 10:28 AM   #2
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IF YOU ARE ASKING HOW TO MEASURE the case wall thickness, use a tubing micrometer.
IF you want to know the OD of the hole itself inside those case walls use a pin guage that can measure it to a tenth/thousandths with a tenth mike.
OR are you saying something else here ?
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Old March 25, 2013, 10:45 AM   #3
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Thanks for the reply. It is the case wall thickness I am trying to measure.
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Old March 25, 2013, 10:52 AM   #4
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Probably the easiest way to measure the inside of a case neck with what most people have on hand is to measure the OD of the case neck with a caliper or even a micrometer, then measure the case wall thickness with a caliper and subtract twice the case neck thickness from the OD to get the ID.

BUT, when you do that, make sure that you take the measurements multiple times at the same place as well as multiple places on the same case neck. Multiple times at the same place allow you to see how much variability resutls from your tools and technique, while doing it at multiple places will allow you to see how much variation is really in the metal you are trying to measure.

You will probably find that the OD varies by a several thosandths, due to TWO causes: the inside opening is probably slightly oval, and the neck thickness is not uniform around the circumference (or even along the length) of the neck. So, this will give you some idea of the UNCERTAINTY of your measurements, as well as what is contributing the most to that uncertainty.

You could use pin gauges, but they will tell you only the diameter of the smallest circle that can fit into what may be an oval opening. The same goes for the inside diameter measurement devices that expand to fill the holes and then either have a direct readout or are "locked" and removed from the hole to be measured by calipers or micrometers.

For case necks, gettiing measurements of either thickness or diameter to finer than 0.001" should not add anything to your reloading capabilities.


Last edited by SL1; March 25, 2013 at 07:25 PM.
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Old March 25, 2013, 01:13 PM   #5
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I use a tubing micrometer (aka, ball end micrometer) for this. I find it easier to get reading consistency with the micrometer held in a micrometer stand than held freehand, but these are cheap (Harbor Freight used to have one like this for $10 at one point, though I don't see it there currently). They don't sell tubing micrometers at HF, though. At least, not that I've seen so far. That means that if you really want to go digital, you will be out some money for such a tool. A vernier scale unit may be had for a sixth the cost.

I usually find the amount of brass in necks is similar and therefore if they are thinner than average on one side they are thicker than average on the opposite side. This can be seen on a runout gage, as the indicator hand goes up and down fairly uniformly.
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Old March 25, 2013, 01:35 PM   #6
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I don't own a ball micrometer, yet, so I use a machinist's magnetic base with a dial indicator. I nestle it up to my case trimmer, and after sizing my cases, I put a case in the trimmer and rotate it while the dial indicator is positioned against the trimmer pilot and, therefore, the case neck.

This only works after resizing, or more specifically after the expander ball has made the inside round, pushing all excess material outward to be read by the dial indicator. It's not as accurate as a ball micrometer, but its the same principle as the Hornady and Forester gauges.
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