Chronographing Basics For Shotgunners by L.P. Brezny

Making use of a chronograph to check loads from a benchrest.

I started using a chronograph recorder about 35 years ago. For those who may not know, a chronograph is an electronic machine that measures the speed of moving objects through the air. In those days, it was quite common among ballistic types to chronograph rifle and pistol bullets in flight, but the art of shotshell chronographing was so young most gun writers believed it was not only impossible to do but, if any information was gained by recording shotshell pellets in flight, it would be less than trustworthy and, in most cases, useless.

With that encouraging piece of information in my back pocket, I headed out onto an old airfield and, for the next three years, worked at perfecting the art of measuring shotshell pellets in flight from the muzzle of a smoothbore and downrange flight speeds, as well. “Downrange” being whatever distance at which I wanted to learn the exact velocity of a given pellet size matched to the muzzle velocity, pattern dispersion and a number of other related ballistic elements.

At first my tests were so meager in terms of success, I did not share my results with anyone. I was shooting by way of some very old, hand–me–down equipment that required me to shoot through a very small 3" window at whatever range I was testing then use a pre–developed table to turn a bunch of raw numbers around and find the exact velocity of my recorded pellet speed. It would take almost every page in Shotgun Sports to even start to talk about what the whole measurement process involved. The more I failed or came away with only a little information, the harder I worked.

My real break came when Doc Oehler, inventor of the Oehler Chronotech velocity–recording system, came along. Doc had designed a system that was user–friendly and returned far more information than anything I had seen, even in commercial production, up to that time. Today, the Oehler Chronotech System is used by ammunition manufacturers when bringing commercial loads together and the U.S. Army when testing anti–tank rounds or main–gun tank rounds. I think the Oehler System is second to none in terms of output, design and being as tough as a bulldog.

Muzzle Velocity & Downrange Recording

The manufacturer of any chronograph system will include directions to get the system up and running. You don’t ever want to press the muzzle of your shotgun directly over or close to the first velocity–recording screen. If you advance the muzzle too far, it will result in “error” recordings, and the muzzle flash will cause the system to react incorrectly. You must keep the shotgun muzzle at least 3 feet back of the first screen. This won’t give you the exact muzzle velocity, as shot speed falls off very fast after exiting the barrel, but it is a very positive indicator of how your loads are doing in terms of uniformity and peak velocity.

You will notice when you read published velocity figures the writer usually indicates a 2, 3 or even 4–foot spacing off the first screen for the position of the shotgun or rifle muzzle. Various computer programs can correct to the exact velocity for you; however, it is not often critical to do so.

When using a chronograph system to determine smoothbore muzzle and downrange shot–cloud velocity, you have to remember to armor (protect) the system to keep stray pellets from damaging the recording screens. Regardless of the chronograph system, screens must be shot across to gain the start and stop time and then allow a built–in computer to return the velocity in f.p.s. (feet per second) measurements.

L.P. Brezny

Knowing your loads produces results. A good chronograph system can help you gain the most from your gun/load combination.

If the chronograph can’t be used with the overhead sun filters removed, you may have a problem. The Oehler’s screens can be “de–horned” when testing is done at a low sun angle (i.e., early morning or evening) or on a cloudy day and no overhead screen armor is necessary, but armor for the photo cells themselves is required. I use heavy 5/8" cast–steel railroad–tie plates 8"x8" at an angle of 35 degrees against the incoming side of the photo cells. This will stop a 180–grain .30–06 bullet at 100 yards downrange and, to date, no smoothbore shot of any type has moved the plates. The heavy steel plates are supported by taping them to a pre–built rail/ramp on a pine 2x4 that acts as a retention system and is also armored with 3/8" plated aluminum for lighter duty work with fine lead shot at medium ranges (40 yards). A word of caution: Always remember to also protect the unit by digging into the ground or using heavy wood or steel plates around the chronograph cables. Any exposure to incoming shot can result in damage that will require new cables, as splicing them is not an option.

As to the chronograph computer itself, move it well away from the impact zone. The Oehler is well–designed for such work. In some units, the computer is a tight package built right into the screen housing system. Oehler units can usually be placed many yards away from the screens themselves.

Who Needs To Chronograph

Do you need to chronograph when handloading your own ammunition? The answer is no, but it is nice when you are trying to gain the very best out of a top–end target load or field loads. Handloads can change even with the use of different lot numbers in propellants. A change to a different hull can make your pet load come unglued. Chronographing can work like a personal detective agency, allowing you to build closer–to–perfect ammunition at your handloading bench.

Those who read my articles on a regular basis know the chronograph system is often used to cross–check handloads and factory ammunition during reviews of ammo. At times, I have found problem areas by way of the chronograph that would have gone undiscovered if that system had not been employed.

With the recent developments in both sub–sonic (quiet) shotshell ammunition and low–recoil loads, the handloader can match these newer loads by working with a chronograph system. By keeping velocities at the muzzle close to 950 f.p.s., recoil is greatly reduced, energy is maintained at a high level to 40 yards, and the sound is also better controlled (see reloading manuals for published data to test). When I get calls from readers in regards to loading their own low–sound/low–recoil ammunition, the first thing I ask them is if they own a chronograph unit. If not, there is a problem in “fishing” for the best load.

In training loads, you need enough steam to produce positive results downrange but not so much that the shooter develops a flinch. Again, a chronograph can help match the load to the gun and shooter by giving the handloader the correct amount of velocity to get the job done but not in excess. (Again, check reloading manuals for published data to test.)

If you own and use a chronograph, you may find the books say one thing, while the chronograph may tell you something very different. The use of modern home–based chronographs has changed the way reloading data and factory–load specs are presented today. Chronographing is not for everyone, but the data it produces can be very helpful in load choice and development. Understanding how the systems work helps you better understand the data you read on ammo. Knowledge makes you a better reloader or ammo buyer.

L.P. Brezny has worked in research and development in the shooting industry for 19 years. He developed and marketed the first sub–sonic shotgun and shotshell — The Hastings Metro™ Gun System — and was the first to measure shotshell pellets in real time at target distances, building ballistic tables demonstrating shotshell load performance and chronographing systems. He also developed the Dead Ringer® high–performance waterfowl/upland choke–tube system. L.P. has been writing for various shooting publications for over 20 years.