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Ammo Checkup: How to Identify Ammo Cartridges Not Up to Par

The Hornady Measurement Station will tell you critical things about your ammo and ultimately help you achieve more consistent groups.

Ammo Checkup: How to Identify Ammo Cartridges Not Up to Par

Hornady’s new Precision Measurement Station measures critical ammo aspects such as bullet runout (shown here), ogive-to-cartridge dimensions and headspace consistency. (Photo courtesy of RifleShooter)

An old accuracy adage pinpoints the importance of quality in the “Three Bs” — barrel, bullets and brass — when searching for ultimate precision. Hornady’s new Precision Measurement Station can’t do anything about the first, but it sure can help handloaders determine whether quality in bullets and brass is present.

This instrument does not fix problems. It finds them. It helps the handloader sort projectiles and cartridges for dimensional consistency and in some cases determines exactly where corrective action is called for.

Hornady was kind enough to send me an early-production sample for review. It’s an impressive unit right out of the box. Weighing in at eight pounds, it’s got enough inherent weight to be nice and solid on the bench, and leveling feet enable the user to optimize positioning and stability. Additionally, those feet are rubberized, which helps keep it in place on the bench.

The station’s comparators measure seated-bullet concentricity, bullet (or cartridge) base-to-ogive length, and cartridge headspace length. Those are the big ones. Additionally, it can measure cartridge case length, bullet diameter, case mouth squareness and other small but useful measurements.

These measurements are helpful not only to handloaders but also to shooters sorting factory ammunition for best performance—or comparing one brand of factory ammo to another in order to discover which is most consistently assembled. Let’s take a look at each of the three most significant operations the Precision Measurement Station performs.

Bullet concentricity is important because it determines how straight—and how consistently straight—projectiles are presented from the chamber into the rifling leade. If a bullet starts into the bore cockeyed, it will either stay crooked or get cranked straight by incredible forces as the rifling centers it up. Either way, the bullet gets distorted, compromising ballistic coefficient, and flight characteristics are compromised. This won’t occur if your bullets are seated reasonably straight.

The station can’t fix cartridges with unconcentric bullets, but by calling them out, it can help you finesse and adjust your reloading press and seating die to eliminate or minimize the runout. In the case of factory ammo, it can tell you which loads are straightest.

To measure concentricity, adjust the station as outlined in the manual, lay a cartridge on the ball bearing rollers, and roll it gently while watching the precision dial. While testing for this article, I measured factory ammo in .300 WSM by two different manufacturers, .303 British by two different manufacturers, and a batch of 6mm GT handloads.

Initially, I was shocked at the amount of runout displayed by all, and then I took a closer look and realized the dial is marked in .0005-inch increments, not .001. Still, it’s thought-provoking when you discover even your match handloads average .003 inch of runout, and most factory loads average .007 to .010 inch.

Bullet base-to-ogive length is important because significant variation can affect the bullet’s relationship to the rifling leade—how much it jumps to the rifling or, in the case of some match handloads, how much it engraves into the rifling. Length variation also affects how consistently the bullet’s base intrudes into powder capacity.

Variation in any of these relationships introduces variation in your pressure curve, which translates into variation in muzzle velocity. Extreme spread and standard deviation broaden, leading to high and low impacts at long range. Plus, seating depth is known to directly affect accuracy, so group size can open up.

To measure bullet base to ogive length—or cartridge base to ogive—remove the ball tip from the dial indicator and replace it with the flat attachment. You’ll find it screwed into the top of the tall, half-inch steel indicator shaft the dial is attached to.


Hornady redesigned the ogive comparator gauge set included with this unit, optimizing it for the long, high-ballistic-coefficient bullets that perfection-obsessive handloaders are most likely to use with it.

Included bullet ogive comparators are .224, .243, .257, .277, .284 and .308. Install the correct size in the hole machined left of the “H” logo on the station’s work surface. Place a projectile or loaded cartridge into the comparator gauge and adjust the dial as instructed in the manual. Be sure the bullet or cartridge’s base is square to the dial sensor’s flat face and read the dial. Repeat with the rest of your bullets or cartridges.

Here’s where handloads showed distinct superiority to factory ammo. Over a series of five consecutive measurements, I found at least 0.015 inch of length difference in all the factory loads I tested and as much as .025 inch in some. Match-grade 6mm GT handloads assembled using premium dies and a competition-grade, micrometer-equipped seating die exhibited less than .002-inch variation.

The Hornady station also measures cartridge headspace variation. If there’s variation in the distance between the cartridge case head and the datum point on the shoulder, it directly affects the positioning and presentation of the projectile into the bore. This can have a significant detrimental effect on accuracy.

Included headspace bushings are .330, .350, .375, .400, .420. These will measure nearly all cartridges of .358 and smaller bullet diameter. If your cartridge isn’t listed, pick a bushing with a hole sized so it contacts near the center of the shoulder. Install the bushing small-side down in the hole machined to the right of the “H” in the work surface. Place a cartridge nose down in the headspace comparator and adjust the dial and flat sensor attachment as instructed in the manual.

Make sure the flat face of the sensor is square to the base of the cartridge, and note the measurement. Test all your loads or simply get an average.

As mentioned, headspace is a dimension critical to safety and reliability, and I wasn’t surprised to find less than .0015 variation within most premium factory ammo and less than .003 even in “Walmart” loads and in rimmed cartridges such as the .303 British, which technically headspaces on the rim rather than the shoulder of the case. Handloads, with one exception, measured a scant .0005 over a series of measurements.

Recently, while testing a new 6.5 Creedmoor precision rifle, two cartridges in a box of 20 refused to chamber in a new rifle with a minimum-dimension match-type chamber. I measured the headspace of the cartridges that did chamber. All were within .003. Then I measured the two stubborn rounds. One was just over .005 longer than the acceptable spectrum, and the other was .008 longer. Clearly, it was enough to prevent chambering.

I’ve gotten along without a Precision Measurement Station for a long time, but in the short time I’ve been using and testing this one, I’ve learned some surprising and enlightening things about bullets and ammo. At $325 suggested retail, it’s not cheap, but for handloaders serious about accuracy, I think it’s an indispensable tool.

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