Chronographs: What's All The Fuss and How They Are Useful

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Handloaders often consider velocity as something to maximize with their handloads, not as a metric by which to refine performance. However, it’s one of the most useful tools for tuning your reloads. Becoming a student of velocity and the way it reacts to propellant charge weight, bullet seating depth, case neck tension, case mouth crimp and so on can benefit accuracy. And how does one accurately measure velocity? With a chronograph. For those unfamiliar with how these tools work, at its base a chronograph is a precision time-recording instrument. Shooting-related versions convert time of flight into speed of the projectile.

Traditional chronographs utilize electronic eyes and a timer to record how long it takes for a bullet to pass between the eyes. These still work quite well.

Oehler Research’s Model 35P is still the consumer chronograph by which all other chronographs are measured. However, it’s big and time-consuming to set up.
Competition Electronics makes a much smaller unit called the ProChrono that’s easier to transport and set up—and much easier on your wallet. Of course, it’s less precise, too, but for most shooters it’s plenty accurate enough.

Another type relies on magnetic fields to detect the speed of a passing projectile, such as the MagnetoSpeed V3. It’s a compact, useful tool that installs on your rifle’s muzzle, bayonet-style. As such, it’s not useful for handguns and really hard-kicking big-bore rifles. More recently, radar-equipped chronographs have owned the scene. These range from $550 consumer versions by LabRadar to $80,000 professional devices employed by ammunition manufacturers. Notably, Garmin just introduced its Xero C1 Pro; it’s the most compact and potentially user-friendly consumer chronograph of them all.

3 Important Numbers

Whatever chronograph you employ, you’ll get three velocity-related numbers useful for load tuning. The first, and most commonly used, is average velocity. While you're firing a string of five or 10 rounds (the more the better), the device will record individual velocity for each and will generate an average velocity. This number is useful for three things. It will tell you if you’re achieving at or near the maximum velocity potential of your cartridge in your barrel length—one thing many handloaders strive for. Velocity average can also provide insight on chamber pressure. If your handloads with a given powder are significantly exceeding velocities published in reloading manuals, you are almost surely exceeding safe pressures. Yes, even if there are no warning signs such as flattened primers, stiff bolt lift and ejector swipe. Velocity average is also crucial for calculating long-range ballistics. This is the number you’ll plug into your ballistic app to get your come-ups when shooting faraway targets. Hunters, of course, also use these apps, and they can plug velocities into the onboard ballistic engines incorporated into in many of today's rangefinders and supply them for custom dial-up riflescope turrets as well.

The next most useful number the chronograph provides is standard deviation, usually noted as SD. This is more or less what it sounds like: the statistical spread of velocity from the mean. Handloaders strive for an SD in the single digits. Factory ammo that provides an SD in the teens in your rifle is entirely acceptable. If your handloads have wide SDs—let’s say anything in the high teens and up—some tuning will be beneficial. Some conditions that exacerbate SD spreads are propellant charges with a low fill density, inconsistent case neck tension and inconsistent case mouth crimp. Choose powders that provide nearly full to lightly compressed density. Use a match-grade sizing die with exchangeable bushings to optimize neck tension. If you’re going to crimp, trim every case to identical length before reloading.

There’s more to the SD aspect of handloading, more than we can tackle here, so let’s continue on with what velocities can tell you. A chronograph also provides extreme spread, usually termed ES. This metric is a bit less tangible than velocity average and velocity SD, and can be harder to draw useful conclusions from. What I find it useful for is keeping tabs on chronograph performance and handload quality.

A good ES should be around 2.5 to three times the number of your SD—let’s say between 15 and 75 fps. If you’ve got an unexpectedly large ES, scroll through and check each velocity measurement.

Helpful, Not Perfect

Chronographs are not infallible, and occasionally they’ll clock a number that just doesn’t make sense. If you’ve got a high or low reading that is, say, 80 or more fps away from the next nearest number, it’s likely either a faulty handload (that’s on you), or a faulty measurement.

I’ve seen otherwise consistent shot strings with one drastic outlier, sometimes as much as 300 to 400 fps out. Delete that shot to see the correct measure of your load’s speed and consistency.

If, on the other hand, your load has a large ES—say 100 fps or more—and a really broad SD, for example 30 to 50 fps, that’s probably an accurate representation. I usually see really wide spreads like this only in handguns or very short-barreled rifles, where it’s sometimes unavoidable.

All these things can seem a little abstract compared to the tangible size of a group on a 100-yard target. However, they’re all connected—and the farther you shoot, the more important velocity consistency becomes. Use a chronograph, refine those numbers, and you’ll reap the rewards downrange.

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