January 04, 2018
By Scott E. Mayer
I'm greatly troubled when gun writers don't do their homework and repeat misinformation that intuitively seems correct, but that has been proven incorrect time and again. Gravity being the bugaboo when shooting uphill or downhill, and slow but determined so-called "brush-buster" bullets are among the subjects most often gotten wrong in print. Another is the importance of shot string length.
When a load of shot is fired from a shotgun, the pellets disburse radially to form what we see two dimensionally as the shot pattern on a sheet of patterning paper. What isn't as easy to perceive, is the front-to-back distribution of the pellets that results in the cigar-shaped "cloud" of pellets called the shot string. Intuitively, you can envision how a short shot string seems beneficial because more of the pellets would appear to arrive on a moving target at the same time. Conversely, a long shot string strung out across the sky would appear to allow a bird or clay pigeon to pass through just a small section of the string.
I was fortunate enough a few years ago to be involved in an experiment conducted at H.P. White Laboratories in Street, MD, dealing with the external ballistic properties of a typical Hevi-Shot "duck load." One part of that experiment required determining the length of a Hevi-Shot shot string at 40 yards, and then comparing it to the shot strings of steel and lead loads also typical of what would be used for ducks.
When Burrard did his shot string experiments in the 1920s, he attached a steel plate to the side of a truck that an assistant drove past him at about 40 miles per hour. Burrard shot the truck as it drove past and using the velocity of the truck and the downrange velocity of the shot accurately calculated the length of the shot string from the elliptical pattern it made on the steel plate.
Burrard's method was simple and it worked, but to determine the length of the various shot strings at H.P. White, two high-speed digital cameras and a Remington Model 11-87 shotgun were used in conjunction with an Oehler Model 55 Skyscreen and a tape measure. The experiment was set up by mounting the Remington in a rigid fixture to ensure a constant impact point. One of the cameras and the Oehler screen were set up downrange at 40 yards with the camera's shutter set so that it was tripped when the first pellet crossed the Skyscreen.
The second camera was set to photograph simultaneously but was positioned a few feet up range, closer to the shotgun. As we fired each load, the up range camera was moved closer to the shooter until shot pellets were no longer consistently visible in its photos at which point the camera was moved back down range until pellets were again visible. Such arrangement made it possible to photograph both the front and back ends of the shot string at the same instant, and then to simply view the tape measure through the cameras' viewfinders to measure the distance between the two images to come up with the shot string length. Several boxes of each type of ammunition were fired to determine an average shot string length.
It's important to note here that most shot string testing within the industry typically focuses on 80 percent of the shot string rather than the entire string. The reason for this is that in a shot string it is typical to have a few pellets leading the pack by a considerable distance and to have a few stragglers lagging behind. Measuring only the 80% that makes up the bulk of the shot string cancels inconsistencies caused by such over- and underachieving pellets. The testing I was involved in related to extremes, which is why 100% of the shot string was counted and is convenient to illustrating the downrange significance of shot string length here because of its exaggerated length.
As expected, the H.P. White experiment showed that there are significant differences in the shot string lengths of the different loads. Both Number 4 Hevi-Shot and Number 4 lead shot strings were consistently between 11 and 12 feet long at 40 yards. Number 4 steel was noticeably shorter measuring between eight and nine feet long, while Number 2 high-velocity steel had the shortest shot string ranging between seven and eight feet long.
Physically, it should be obvious that there is a great difference between a seven-foot steel shot string and a 12-foot Hevi-Shot shot string. Intuitively, one can envision the short string making more hits on a moving target and that would be the case if the shot string suddenly froze in midair when the target got to it, or if the target and shot string were at or near the same velocity. But the shot keeps moving, and even the fastest birds don't approach the velocity of the shot.
Another part of the H.P. White tests involved measuring downrange velocity of the various loads. Measuring the velocity of a shot string is not nearly as easy as a single bullet. Pellets in a shot string are all moving at a different velocity and that has to be accounted for or you
simply have to be satisfied with using the velocity of the pellet (singular) that trips the downrange chronograph screen. To try and account for the velocity of the entire shot mass, we initially incorporated an oscilloscope into the test apparatus reasoning that as each pellet passed over the chronograph screen it would register a spike from which the respective velocities could be calculated. What we hadn't anticipated, though, is that Oehler chronograph screens have a built-in suppressor that shuts them down for an instant after a bullet passes so that you don't get a false, secondary reading from the blast or shock wave. That being the case, we had to settle for simply firing enough loads across chronograph screens at 40 yards to come up with a reasonable average of velocity.
Downrange velocity was also calculated using the muzzle velocity of the various loads taken using an Oehler Model 71 (a device that does account for the entire shot string), the mass of a respective pellet and the ballistic coefficient of spheres. Those two methods resulted in similar numbers that were very close to those published in industry literature for the various loads. Specifically, the average 40-yard velocity for Number 4 Hevi-Shot was taken as 920 fps, Number 4 lead and steel were 803 fps and 699 fps, respectively, while Number 2 high-velocity steel was still going 845 fps.
With the length of the shot string and the downrange velocity of the shot known, we can plug those figures into real-world conditions and decide for ourselves if shot-string length is of significant value. Take for instance a duck flying at a right angle to the shooterâ€” let's make the duck a teal as I find them particularly easy to miss. According to information from the Northern Prairie Research Center, the "common flying speed of ducks and geese is between 40 and 50 miles per hour." We'll give our teal a velocity of 50 M.P.H. (73 fps), and take a crack at it from 40 yards using the Number 2 high-velocity steel with its seven-foot shot string going 845 fps. At that distance, the shot is moving one foot every 0.0012-second, so it takes 0.0084-second (7x0.0012) for the entire seven-foot shot string to cross a given point in the sky. Our teal covers a distance of one foot every 0.0137-second. This is about a 1:12 ratio meaning that for every 1 foot the duck flies, the shot string moves 12 feet. If both the teal and the shot intersect in the sky at exactly the same moment, the teal moves about 1/2 a foot in the same amount of time it takes the entire seven-foot shot string to cross the teal's plane.
What about a long shot string? Switch from the Number 2 high-velocity steel to Number 4 Hevi-Shot and use its numbers to find out. The Hevi-Shot shot string at 40 yards is 12 feet long and going 920 fps, so it covers a distance of one foot every 0.0011-second (1Ã·920). The entire 12-foot shot string, then, passes a given point in the sky in 0.0132-second (12x0.0011) making the target to shot ratio almost 1:13. If we shoot at our teal with this load, we see that the teal flies a total distance of about one foot in the same amount of time it takes the entire 12-foot Hevi-Shot shot string to completely cross its plane.
Clay pigeons move considerably faster than live birds, so would shot string length make a difference on the target field? I believe International skeet move out of their respective houses at a smoking 90 mph (132 fps), but with the ballistic coefficient of a child's art class ashtray, lose their velocity quickly. According to data published in Lyman's Shotshell Reloading Handbook 4th Edition, Number 9 shot is going at 820 fps at 20 yards. With a nearly 1:8 ratio, you can already see where that one is going, so let's stretch things out to exaggerated extremes by keeping the target going 90 mph for its entire flight, use Lyman's published 40 yard Number 9 shot velocity of 625 fps, and make the shot string ten feet long. That's less than a 1:5 ratio.
Given those conditions, if the two meet in the sky at the same time, the clay will move 1 foot every 0.0076 second and the shot string one foot every 0.0016 second. The entire exaggerated shot string passes the clay in 0.016 second, while the clay moves only a little more than two feet. If we consider the significant target zone for the clay bird to be the standard 30-inch circle the entire industry uses for patterning and gauging pellet distribution, it's easy to see that even if the target velocity is increased and the shot string velocity decreased to unrealistic levels, and the shot string length extended out to extremes, that shot string length still doesn't matter.
So what does matter and what does all the math mean to a shooter? It means don't sweat the shot-string length. Instead, divert that energy to patterning your shotguns with the loads you intend to use in the field. Look for "holes" in your patterns or for uneven distribution of shot. It's those holes a bird really can escape through, so plugging those holes are what make the difference between a hit and a miss.