Extreme accuracy demands consistent case necks. If your case neck walls are thicker on one side than another, your bullets can be positioned off-center in the chamber, or tilted slightly off the bore axis. That means your bullets can actually start off crooked as they enter the barrel. (And “jamming” bullets into the rifling won’t necessarily correct the problem.) If some of your case necks are significantly thicker than others, it will be difficult to maintain consistent neck tension from one round to another. That can kill accuracy in a number of ways. Likewise, widely varying neck tension can cause nasty swings in cartridge pressures and velocities.

Of course, in a given lot of brass you will probably see a combination of these variations–both case to case differences in average wall thickness and lack of uniformity on individual cases. That is why it is so important to measure your case necks, even if you shoot no-turn necks. With a good case neck wall measuring system you can cull the worst offenders, and then segregate your brass according to neck thickness.

Lyman Ball Mic (.0005″)

Shown at right is the inexpensive Lyman Ball Micrometer, item 7832252. It retails for about $42.00, complete with plastic storage box. Lyman claims it offers .0001″ (one ten-thousandth) resolution, but users tell us the practical accuracy is maybe half a thousandth. As with most ball mics, the Lyman features a ratchet stop and spindle lock. This unit is pretty small and can be a bit awkward to use without a supporting clamp. The photo shows a method of holding the tool in the base of your palm. User reviews of this tool have been positive, but it can be a bit tricky with short-necked cases.

One MidwayUSA purchaser reports: “It is difficult to measure the thickness of very short-necked cases, like the .204 Ruger and .223 Remington. That’s because the spindle’s thickness is quite close to the length of the case neck. Be careful that the spindle doesn’t stop against the shoulder of the case.” This issue could be resolved by tapering the end of the spindle like Jason did with his Mitutoyo mic shown above.

Holland Neck Thickness Mic (.0001″)

The new">Holland Ball Mic was one of the first purpose-built neck thickness mics for reloaders. Darrell Holland claims the “soft-touch” ratchet system allows repeatable measuring to .0001″. The slim, football-shaped ball anvil allows the mic to be used on cases as small as .17 caliber. The $75.00 Holland Mic is more expensive than the Lyman, but the Holland tool is easier to hold, and a matching “Third Hand” clamping base is available for $30.00. As a system, the Holland Mic and Base comprise a nice set-up for around $100.00.

The manual version (Model 569, $139.00) has a resolution of one-thousandth of an inch (.001″). This is adequate for sorting brass. However, if you are turning your case necks, you’ll prefer the superior resolution of the model 769 digital version which reads down to .00005″, half of a ten-thousandth (i.e. 50 millionths). Few reloaders can turn necks to that level of consistency–but it’s nice to know you can measure that closely. Still, that kind of precision doesn’t come cheap–the model 769 costs a hefty $436.00.

While tubing mics allow rapid measurement of tube walls, they provide a longer contact section on the inside of a case neck. This gives you less precision when trying to measure a specific position along the neck. Likewise, a tubing mic is intended for use with straight tubing sections only. Cartridge case necks can taper a bit, and for this reason we recommend using a ball mic rather than a tubing mic, particularly when measuring factory brass that has not been neck-turned.

Redding Case Neck Gauge (.001″)

The Redding Case Neck Gauge, item 26400, is one of the better tools on the market for measuring neck-wall thickness. It is fast, repeatable, and accurate. When turned and unturned necks were checked first on the Redding tool and then double-checked with a Starrett ball mic, the results were the same–but of course the Redding Gauge can sort multiple cases more quickly. The Redding Case Neck Gauge is similar to the Sinclair Gauge above, and likewise offers .001″ resolution with a dial indicator reading off the case neck. The distinguishing feature of the Redding unit is the horizontal base which is pre-drilled for mounting on a bench. This non-removable horizontal foot can also be placed in a vise, or held with a Redding double “C”-clamp (item 30520), if you prefer not to mount the Gauge permanently to your bench. While the Sinclair Gauge would normally be placed horizontally on a flat surface, the Redding Gauge stands vertically, making it a bit easier to see dial indicator marks.

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Redding provides the dial indicator with its tool, along with two mandrel shafts that have a narrow tip that runs through the flash hole. The mandrel tip helps index the case on the pilot and prevents the case from rocking as you rotate the neck under the dial indicator. The small 9/64″ mandrel is for calibers down to .17 and cases with small flashholes. The larger 3/16″ mandrel will measure up to .338 caliber cases. One nice feature of the Redding Gauge is that pilots are precision ground from stainless steel. The Redding Case-Neck Gauge ships complete with a .001″ Dial Indicator and two pilots (.22 and .30 caliber). If you shoot a 6mm, 6.5mm, or 7mm, you’ll need to purchase a separate pilot. With an MSRP of $96.00, this unit typically sells for $78 to $84.00. Right now, Midsouth Shooter’s Supply has the Redding Case-Neck Gauge, item 076-26400, on sale for just $56.88, including two mandrels and both .22 and .30 caliber pilots. That’s a very good deal while it lasts.

K&M Dial Indicator Attachment

One nice feature of the K&M neck-turning tool is that you can attach a dial indicator directly to the neck turner, opposite the cutter tip. In theory, this allows you to get a direct, constant read-out as you neck-turn your cases. In practice, we’ve found that it’s better to measure your necks after the cut, particularly if you use power while turning. The dial indicator assembly changes the balance of the tool, making it a little more difficult to hand-hold while turning. Also, the brass tailings, lube residue, and small chips that build-up during cutting can interfere with the dial indicator. We don’t recommend using the K&M tool for bulk-sorting brass prior to neck-turning. First, this would require you to back away the cutter tip, which means you lose your cutting setting. Second, the neck-turning mandrel is precisely sized to be a pretty tight fit on brass that has been full-length sized, then expanded with a K&M expander mandrel. If you start with unsized brass, the fit on the mandrel may be pretty sloppy. Conversely, if you full-length size and then expand the brass (as you would in preparation for neck-turning), the fit on the mandrel is going to be pretty tight, and that will slow you down if you’re trying to sort many dozens of pieces of brass.

Nielson Neck Checker (.0001″)

Don Nielson, creator of the Pumpkin Neck Turners, sells a simple but very effective tool that offers both .0001″ precision and ease of use. You just slip the neck of the case in the center of the round tool base, and a .0001″ dial indicator reads the neck thickness quickly and easily. Nielson’s neck checker is pricey at $150.00, but this device combines the precision of a ball mic with the speed of one of the “quick-check” gauges, making this tool suitable for both rapid-sorting of bulk brass AND checking brass that has been painstakingly turned to sub-thousandth of an inch tolerances.