Tools for Measuring Case Necks
Consistent Necks Enhance Accuracy
After your calipers and reloading scale, a neck wall thickness gauge may be the most important measuring device on your reloading bench. If you want to shoot tiny groups, you need ultra-uniform necks, with consistent neck wall thickness. It’s not surprising that the most accurate rifles in the world, short-range PPCs, almost universally use turned case necks because properly-turned necks offer ideal neck wall uniformity. But even if you shoot “no-turn” necks, you need to be able to measure your case neck wall thickness accurately. A good ball micrometer or neck wall thickness gauge will let you cull non-uniform brass, or set it aside for “clean-up” work. For a “no-turn” solution to work, you still need necks that are very uniform, with consistent thickness.
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.
Take any two cartridge cases out of the box, and you will see variations in neck wall thickness and uniformity, even with superior brass such as Lapua. With low-quality brass, the variations may be extreme. We’ve seen Remington brass vary up to .004″ in wall thickness within the same box.
The illustrations at right show the two basic problems with neck walls. First, the neck walls on some cases, even if they are uniform all the way around, will be thicker than on other cases. This hurts accuracy because it is virtually impossible to maintain consistent neck tension with brass of varying neck wall thickness. Yes, you can try to adjust tension using different bushings, but it is much better to start with brass that has the same wall thickness.
Even if a batch of brass has the same average wall thickness, give or take a thousandth, you can still have problems if the neck walls are not uniform. This is illustrated in the second diagram. Neckwalls can be thick on one side and thin on another. The only way to “cure” this problem is to turn the necks.
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.
If you turn case necks, and try to hold wall thickness variation to half a thousandth or less, here’s a superior tool. Sinclair’s Digital Case Neck Micrometer measures neck thickness to 0.0001″ on all calibers from .17 all the way up to .50 BMG. The unit powers up (and zeros) at the touch of a button, and a large friction barrel makes it easy to adjust the contact pressure or “feel”. You can change the measurements from SAE to Metric by pushing the other button on the digital head, and the unit will shut down after five minutes of non-use. By rotating the friction barrel, the unit re-activates without losing the zero, data output, and absolute or relative measurements. The unit, item 09-900, is very stable, and you can tilt the display head for easy viewing. That digital read-out is a huge plus for older eyes, trust us. Sinclair’s Digital Mic normally sells for $196.00, but it is now available at “Holiday Sale” pricing for $176.00.
|Nielson Neck Checker||$150.00||Don Nielson||.0001″|
|Redding Case Neck Gauge with Base||$82.00||MidwayUSA, Midsouth||.001″|
|Sinclair Case Neck Sorter with Indicator||$79.95||Sinclair||.001″|
|Sinclair MIC-4 (w/o Indicator)||$29.95||Sinclair||.001″|
|Holland Neck Thickness Mic||$75.00 (stand $30)||MidwayUSA, R.W. Hart||.0001″|
|Lyman Ball Mic||$42.00||Grafs, MidwayUSA||.0005″|
|Mitutoyo Ball Mic||$113.00||Bruno’s||.0001″|
|Sinclair Digital Mic with Base||$176.00||Sinclair||.0001″|
|Sinclair/Starrett MIC-3 with Stand||$134.00||Sinclair||.0001″|
|Starrett 769AXFL Tube Mic||$436.00||J.W. Donchin||.00005″
Photo courtesy Caduceus
|Ball & Tube Micrometers — High Precision, But Slow|
|Mitutoyo (Tapered Spindle) (.0001″)
Mitutoyo ball micrometers are among the best you can buy. The unit above belongs to Jason Baney, our 1000-yard Editor. Bruno Shooters Supply sells them new for $113.00, and you can often find them used at very attractive prices on eBay. Jason’s Mitutoyo mic has been specially modified. Jason tapered the end of the spindle. This creates a smaller contact point for greater accuracy. The tapered spindle also helps when using the mic with short-necked cases such as the 6BRX and Dasher. (With a full-diameter spindle tip, the spindle may contact the shoulder when you’re trying to mic a short-necked case.)
Lyman Ball Mic (.0005″)
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″)
If you don’t have a ball micrometer, a tube micrometer can also be used to measure case neck wall thickness. Tube micrometers (tubing mics) are widely used in industry to gauge the thickess of tubing sidewalls. They are similar in design and handling to ball micrometers, but the shape of the anvil (the section that goes inside the tube) is different. Instead of a ball or football-shaped nub at the end of the anvil arm, there is a polished cylinder of hardened steel or carbide. The diameter of the anvil sets the limit of the smallest tubing hole that can be measured. The Starrett tube mics shown here have a 3/16″ minimum hole size.
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.
|Neck Wall Thickness Gauges — Handy and Efficient|
A dedicated Case Neck Thickness Gauge allows you to sort large quantities of brass with greater ease (and speed) than with a ball micrometer. High-end ball mics can be incredibly accurate, but they are also slow, and somewhat awkward to use (unless you have a secure stand or clamp). The neck thickness gauges reviewed here offer good value. Most of these gauges cost little more than a basic ball mic such as the Holland, and cost considerably less than a premium Mitutoyo or Starrett ball mic. The better neck-thickness gauges are stable and allow you to work with one hand. With ball mics, it seems like you need three hands to do the job right. A good neck thickness gauge/sorting tool allows you to work through large quantities of brass quickly.
TIP: To get the best results with a Neck Wall Thickness Gauge, first iron-out dents in the case necks with an expander. Pilots should be properly matched to the internal neck diameter. Don Nielson tells us .002″ to .003″ clearance works best. Polish the pilot if it is rough. Experiment with the vertical position of the indicator. With most dial indicators, you want some slight down pressure for pre-load, but not too much. When taking the measurement, roll the case smoothly in one direction under the ball. Light lubrication of the pilot surface may be beneficial–but if you use lube, clean your necks afterwards.
Custom Neck Gauge
At right you can see a neck-thickness gauge, custom-crafted by Chris Long, aka “TechShooter”. Chris uses this unit primarily to pre-sort .260 Rem brass for his .260 AI rifle. Remington-brand brass is notoriously inconsistent in neck thickness and uniformity. By using this tool, Chris can quickly short through 100s of pieces of brass, culling those with necks that are too thick, too thin, or which exhibit very poor uniformity.
Techshooter’s neck-thickness gauge has many nice features. It has a nice heavy metal base so it sits securely on the bench, with the dial indicator in clear view. The fixture for the dial indicator adjusts in and out along the case axis so Chris can easily measure different points along the case neck. Chris custom-grinds the pilots for each caliber he sorts. This allows him to get a perfect fit for each type of brass. Note how Chris has also machined a slight relief (reduced radius) on both the inboard and outboard ends of the pilot. Chris noted that factory brass is often thicker near the neck-shoulder junction and it may have a slight flare or lip at the case mouth. Those things can throw off the reading. By reducing the radius of his pilots on either end, Chris ensures that the brass does not touch the pilots at the extreme ends. This way Chris gets a precise reading of the thickness in the middle of the neck.
|Sinclair Case Neck Sorting Tool (.001″)
The Sinclair Case Neck Sorting Tool (Item 59-1000), is this editor’s current favorite tool for quick-sorting brass for a “no-turn” chamber. The Redding Tool below is just as efficient and accurate, but I prefer the portable design of the Sinclair unit. The Sinclair’s .001″ resolution is sufficient for culling non-uniform-necked brass out of a batch. Since I already had a decent dial indicator, the Sinclair Tool only cost $63.50. (It is also sold with indicator, Item 59-1100, for $79.95). Sinclair’s Tool works well either placed on a bench or held in the hand. The black base pad provides a stable, low center of gravity. The mandrel has a narrow pin at its tip that indexes through the case flash-hole. This helps keep the case steady as you roll the neck under the dial indicator. I do load .17- and .20-caliber cartridges, so it’s nice that Sinclair offers an optional ($16.25, item 59-1200) Carbide alignment rod (mandrel) for the micro-calibers. Note, with the Sinclair unit, you do have to pay extra for pilots. Redding includes both a .22 and .30 caliber pilot in its base price.
Redding Case Neck Gauge (.001″)
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
Nielson Neck Checker (.0001″)
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