Using A Chronograph

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To get the most our of your firearm, think about investing in a chronograph

As long as we’re watching for it, an education can come to us from a lot of different sources and it invariably costs either time or money – often both. The hunting and shooting sports are no different. We need to put in the time and effort to learn about the creatures we hunt and the tools we use to hunt them. For those latter lessons, I think the chronograph plays a vital role.

The term chronograph can have several different meanings, but in the hunter’s world it’s an instrument that measures projectile velocity. Note that I didn’t say bullet velocity; that’s because a chronograph can measure more than bullets – arrows, for example. Some of my archer friends are obsessed with arrow speed and are constantly tweaking their bows to gain more feet per second. But this is a gun column, so we’ll leave the archery side to someone who knows what they’re talking about, and in our discussion of chronographs only reinforce that these amazing instruments can measure arrow speed, too.

Bullets, of course, are the most common projectile measured by chronographs. And I suspect the most common goal is to determine velocity so that a ballistic program can be used to generate an accurate drop table. This can be a simple range card taped to a rifle stock or something more elaborate like Leupold’s CDS (Custom Dial System) that allows the shooter to dial the measured range on the scope’s elevation turret to compensate for bullet drop. Whatever form it takes, the trajectory prediction must be accurate. If a bullet’s velocity is only guessed at, that’s all a drop table or a custom scope dial is – a guess. Whether you shoot handloads or factory ammunition, an accurate prediction of a bullet’s trajectory is enough of a reason to own a chronograph.

But ballistic programs, and the optical companies that use them to create custom turrets or elaborate reticles, need more information than just bullet velocity. Environmental conditions are a huge factor in predicting bullet behaviour as well, as is a bullet’s ballistic coefficient. We can collect atmospheric data from weather instruments, but how do we determine ballistic coefficient? Usually, it’s by relying on the data published by bullet manufacturers. But that has limited usefulness, because it is, by necessity, an approximation based on mathematical models and a set of standard atmospheric conditions.

Fortunately, a chronograph can also be used to determine ballistic coefficients. It’s best done with two chronographs, but it can be done with a single unit, it just takes more ammunition. Since ballistic coefficient is simply a measurement of how efficiently a bullet travels through the atmosphere, we can measure that efficiency by measuring a bullet’s speed at two different points. Set one chronograph near the firing line and set a second at the 100 yard/metre line. Get an accurate measurement of the distance between the two units and then shoot five rounds through both, recording the results. Plug the numbers into an online ballistic calculator (I use the free one at jbmballistics.com) and you can calculate your bullet’s G1 or G7 ballistic coefficient. If you only have access to one chronograph, shoot at least five rounds through the instrument near the muzzle. Then set it up downrange and shoot five more to determine both near and far average velocities.

My experimenting with two chronographs has produced ballistic coefficients that are both higher and lower than what manufacturers are listing. A quick record check shows numbers approximately 0.050 under and 0.025 over manufacturer’s listings for G1 ballistic coefficients. But at least these aren’t approximations. These are my bullets, being shot from my rifles, under my conditions. It’s similar to velocity numbers, in that an ammunition manufacturer will predict what velocity their ammunition will produce in the average rifle under average conditions. However, if you really want to know, you have to measure it yourself.

This applies to shotgun ammunition, too. If you’re a handloader it’s a no brainer – you need to use a chronograph to check shot velocities to ensure they are in the range you’re targeting. But it can also be interesting to check velocities of factory ammunition. There seems to be a bit of a speed race in steel ammunition these days, as I’m seeing more and more manufacturers prominently printing velocity on their packaging and using it as a primary selling point. History tells us that once the marketing people take over, truth can become a casualty. I hope that’s not the case here, and the little chronographing I’ve done of shotgun ammunition shows mixed results – some higher and some lower. That figures, as we know shotguns have unpredictable individual preferences about which ammunition patterns best, and I suspect that individuality might apply to which load is the fastest in any given shotgun as well.

Some of my most interesting results have occurred when using the modern chronograph to check velocities of the oldest guns – muzzleloaders. Based on what my chronograph has told me, the list of which factors will change a bullet’s velocity from a muzzleloader can be summed up in one word: everything. Of course, changing the brand or type of any ammunition component can alter velocity; that’s to be expected. But I have one 14-shot test in my records, in which I used exactly the same load recipe for each shot, and still managed a velocity spread of 330 feet per second; I only changed how I cleaned between shots. It taught me that to get consistent velocities from a muzzleloader, I have to do everything the same way, all the time. Without a chronograph, I’d still be wondering why some shots missed the target low.

All of these experiences have convinced me of the value of owning and using a chronograph. There are a number of good brands on the market and more popping up regularly. But whichever instrument one chooses, there’s no doubt that using one will result in an education.

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