|Another ballistics experimentalist and early shotgun writer, Major Sir Gerald Burrard, conducted his own tests in 1923 by shooting at a pattern plate mounted on the side of his Model T Ford. Even in those days, long before the advantage we have today with modern technology and photographic evidence, the results of the experiments revealed that the shot-string was considerably longer from the cylinder barrel than from a choke barrel. This is surprising to most people.|
Finally, one person who has probably done more experimentation in this field than any other is Bob Brister. Bob is a member of the shooting club that I managed in Houston many years ago. The exploits of Bob and his brave wife, Sandy, who towed a moving pattern board on a trailer behind a station wagon at forty miles per hour while Bob shot it, are somewhat legendary. So just what causes this stringing effect, and is it beneficial in any way?
As soon as the charge of powder in a shotshell explodes, the sudden rapid acceleration from rest exerts a massive pressure on the rear pellets. These rear pellets in turn exert pressure on the next layer, and so on. The front layer of pellets is the least deformed in this process, and the rear layer is the most deformed. The small column of shot then pushes up the barrel until it hits the choke area, where more pellets become deformed as the shot charge is accelerated through the constriction I because the outside pellets are deflected inward. Anything that is squeezed from a large diameter to a smaller one is subjected to some degree of acceleration. This is known as the Venturi effect. When the main mass of pellets is forced through some degree of choke, it causes the center of the shot column to be slightly smaller than the diameter of the bore, and it will hold together better after exiting the barrel. The more choke, the greater the cohesion of the pellets over a longer distance. However, the rear portion of the charge begins to disperse more rapidly, for two reasons. These rear pellets have slightly less velocity, and they are more deformed and therefore aerodynamically inferior to the front pellets, which should be more spherical and therefore less affected by air resistance.
The pellets passing through the cylinder barrel are not deflected inward in the choke area, and the small cylinder of pellets emerges from the barrel more or less intact. As soon as these pellets meet air resistance, a drag effect begins to separate the pellets, and because there is no slightly faster central portion to the column of shot, unlike with the choke barrel, this happens quicker with the cylinder barrel. Air resistance does not act on the pellets equally, but acts more on the deformed pellets and less on the perfect ones. The leading pellets protect the trailing pellets from the effects of this air resistance, and these trailing pellets move along behind the leaders. This is why the slipstream effect occurs, but in order to understand this, you need to have a good imagination. Try to imagine a perpetually peeling banana. The front part of the banana represents the forward portion of the shot column, and the skin of the banana represents the outer layer of pellets. These pellets, which are in various stages of air resistance, which is directly proportional to the aerodynamic properties and remaining energy of each pellet, "peel off" in stages. The energy of the leading pellets is dissipated as the pellets hit the air resistance, but the pellets behind these leaders are shielded by them, which has the effect of allowing them to retain more of their original energy. The second layer of pellets will push aside the first layer and overtake them. They may actually collide with the front pellets as I they do this, and by doing so, they create an even wider pattern and longer shot-string. All this passing and catching up continues until either the pellets strike their target or all their energy is exhausted and they fall to the ground.
The result of all this pushing and shoving, in ballistic terms, is that the bulk of the shot will be concentrated in the front end of the string. It also means that the energy retained by these pellets will be directly proportional to their position in the string; in other words, the greatest concentration of pellets and energy retained by each individual pellet will be in the forward portion of the shot-string. Is this significant in normal shotgunning activities? In bird-hunting situations in the field, with shots at extended ranges, a long shot-string is a distinct disadvantage, and any bird that flies into the tail end of a weak shot-string would probably be merely wounded.
So what conclusions can we draw? Pattern density, especially on crossing targets, is more important than you think, especially in wingshooting. A long shot-string is produced at the expense of pattern density. Quality shot will produce a more efficient pattern with less stringing, which will in turn ensure cleaner kills. A shot at a stationary pattern board, with softer, inferior shot (although first impressions may be impressive), is always inconclusive. Economy shells may be perfectly adequate on the skeet field or the quail lease, but at extended ranges, these same shells will be inappropriate and should be avoided. What about on the sporting clays course? Because of the complex and varied target presentations, I believe that 99 percent of the targets we miss are missed due to our inability to put the muzzles in the right place as the shot is triggered-in other words, plain old pilot error. I think it would be difficult to prove conclusively that shot-string is a definite advantage on most of the targets, and the old perception that shot-string is an advantage just isn’t true on anything except fairly close targets-twenty yards or so. As I explained in the section on choke, skeet is one of the few situations where shot-string may give a slight advantage. A few lucky pellets, on occasion, will retain enough energy to chip the front edge off a full, 90-degree crossing target (as these pellets lag behind the main pattern) on an otherwise lost target. With trap disciplines, straightaway." shots, and narrow-angle targets, it is a different story, and this advantage is substantially reduced. For most of our shooting, the length of the shot-string is inconsequential. In the few cases where shot-string does matter, a short one is better than a long one.