Chronographing Metallic Ammunition

You've probably heard them — the reasons for not using a chronograph- — "What the heck do I need a chronograph for, a deer isn't going to know whether a bullet is going 2700 or 2800 feet-per-second when it hits him." Or this one — "I don't need a chronograph because the loading manuals tell me what the velocity is, and that's close enough."

If you hear a remark like one of these, it's a good bet that the shooter has not used a chronograph and really doesn't understand what a chronograph can do for him. It's certainly true that a chronograph isn't required for a given load to bag game, and it isn't necessary to own a chronograph to enjoy shooting. On the other hand, a chronograph is a lot more valuable than most shooters realize.

I've shot thousands of rounds over a chronograph. Even before I began writing about shooting I was using the old silver ink screens which had to be replaced for each shot. In fact, most of the rounds I've fired have been over a chronograph during the past 20 years and I have as good an idea as anyone what velocity a load is likely to turn up. One thing I've learned from all this chronographing is that I really don't know what velocity a load is going to produce from my firearm until I chronograph it. While loading manuals, such as this one, serve as excellent guides to the velocity you're likely to receive, they're only an approximation.

There are a lot of reasons for the velocity variation between published velocity and the velocity you receive from your own rifle or handgun. Firearms are different in terms of throating length and other dimensions in the chamber and bore. There is a considerable difference in cartridge brass thickness and capacity. The performance of each component might vary slightly from one lot to the next. The design of the bullet can affect pressure and hence muzzle velocity. While you can speculate all you want about the effects of various components or a change in barrel length, for example, you really don't know what the effects are without a chronograph. A chronograph cuts through all the speculation and gives you a bottom line figure exactly what your bullet's velocity is.

What a chronograph has to offer a shooter isn't all knowledge, a lot of it is pure enjoyment. It puts a lot more satisfaction into handloading and shooting if you know what velocity a particular load produces. Only then can you compare one load to the next.

With a chronograph you know whether the load you assemble today performs identically with the same recipe assembled last year when you used other lots of components. It can be a type of quality control check on your favorite load.

Besides velocity level, a chronograph is valuable for determining the consistency of a load. A load which produces shot-to-shot uniformity is likely a balanced load, with the primer, case, powder charge, and bullet being well-matched. While accuracy is a result of a variety of factors besides the load, a uniform load has a tendency to shoot more accurately.

If I'm developing a load, I'll generally chronograph several recipes, finding the ones which produce good velocity with a high degree of uniformity. Only then do I take the time to shoot the loads for group (three five-shot strings) on target. I find that this system saves lots of time in load development.

Given a specific bullet, the downrange performance of a load — everything from drop, to wind deflection, to energy, to expansion performance — is dependent upon muzzle velocity. At the same time, there's a lot more information to be gleaned from chronographing than merely the speed of a bullet.

One of the most valuable applications for a chronograph is in keeping loads safer. Loading manuals provide a guide, generally a suggested starting and maximum load. These load recipes are determined by careful loading and pressure testing. Maximum loads are based upon industry standard chamber pressure criteria. Generally speaking, with a given set of components, the higher the velocity, the higher the chamber pressure that is required to produce the velocity. If one of your loads produces velocity in excess of what a loading manual indicates, you can also assume that the pressure is in excess. If the velocity of one of your loads equals the maximum listed velocity in the loading manual (with a comparable barrel length), it's prudent not to exceed the powder charge level you're using, even though the quantity of powder you're using might be less than what is suggested as the maximum quantity in the manual.

While the data published in a loading manual can only approximate the velocity you might receive, the powder charges recommended should be taken as published. An unbelievable amount of time and effort goes into data development for this manual. The loads are pressure tested and checked for other factors to assure that the listed loads are not only safe, but good ones. Always confine your powder charge weights to those recommended in the manual.

Besides velocity, a chronograph can be used to determine the ballistic coefficient of the bullet/load/firearm combination you're using. Put simply, ballistic coefficient is a relative numerical value indicating how well a bullet overcomes the resistance of air during flight.

If you fire a roundnose bullet and a spitzer bullet, both of the same weight and diameter, starting at the same velocity, with both being equally stabilized, the spitzer will arrive on target first. If one mathematically combines muzzle velocity and ballistic coefficient, he can derive precise downrange figures for drop, wind deflection, velocity, energy, and time of flight.

Ballistic coefficient is much like velocity. You don't really know how well a specific bullet flies from your firearm unless you actually test it. Ballistic coefficient can be determined (over the test shooting distance) if a shooter knows the velocity of a bullet at two points, say 12 feet from the muzzle, and 100 yards from the muzzle.

You can use two chronographs, placing one near the muzzle and one downrange, to see the velocity loss for each bullet between the two points and then average the loss. Or you can use a single chronograph and shoot several shots for an average velocity at the near distance, and then move the chronograph downrange and shoot another average at the longer distance. These average velocity figures can then be used to determine velocity loss and compute ballistic coefficient.

You can find the formulas for deriving ballistic coefficient in several sources. I don't like to mess with the math and so I use a personal computer along with one of several ballistics programs to do the calculations for me. PACT (P.O. Box 535025, Grand Prairie, TX 75053) makes a chronograph with a ballistics computer built in.

Remember, ballistic coefficient tells you how fast, relative to other bullets, your bullet arrives on target. The variables here are not only the shape of the bullet, but the velocity, the ambient conditions, and how stable your bullet is when it exits the muzzle. Like velocity, there's no way to know the ballistic coefficient of your projectile without checking it. And like chronographed velocity which cuts through the red tape variables to give you a precise number for your load and firearm, chronograph-derived ballistic coefficient gives you a real number (not a speculation or a theory) for your gun and load.

So far, we've been talking about convential chronographs and what they can do. These range from the compact folding Chrony (Shooting Chrony, Inc., P.O. Box 101, Niagara Falls, NY 14304) with a one-foot screen spacing and the ProChrono (Competition Electronics, 3469 Precision Drive, Rockford, IL 61109) each at about $100, through several models from Oehler (P.O. Box 9135, Austin, TX 78766) and PACT, for just less than $400. There are all prices in between.

Generally speaking, as price goes up, one gains features in chronographs. Today, the ultimate chronograph for the average shooter is the Oehler Model 43 Personal Ballistics Laboratory. As the name implies, the unit is a lot more than just a chronograph. With acoustic target, and strain gauge measuring system, the unit provides information about internal chamber pressure, muzzle velocity, ballistic coefficient, group size, downrange velocity, energy, and a whole lot more numbers with each shot fired. The Oehler Model 43 PBL offers basically all the numbers regarding internal and external ballistics. All this information is captured and stored automatically (as fast as you can shoot it) in a personal computer. The price for this system far exceeds the other chronographs mentioned, yet its cost is not out of reach for a serious shooter.

We've seen that a chronograph can be used to determine a uniform, balanced load that's likely to be accurate. A chronograph can be used to make handloading safer. It can be a means for maintaining quality control of your loads. A chronograph can be used to determine the fastest, most efficient load. It saves time in load development. It can be used to determine ballistic coefficient and predict the most effective load downrange. And it sells for no more than the cost of a rifle. If I were a handloader without a chronograph, I wouldn't purchase another firearm until I had a chronograph. It's one of those things that you don't realize how useful it is until you own one. It's not only informational, it makes shooting a lot more fun.

Hunting Mastery Selected Tips

Hunting Mastery Selected Tips

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Responses

  • kerris
    What impacts the chronographing of ammunition?
    8 years ago

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