By Marshall Williams.
We usually speak of a shotgun pattern in terms of how many pellets a gun will place in a 30 inch circle at 40 yards. We shoot our shotgun at a large sheet of paper, and see that the shot pellets form a roughly circular pattern. We judge the effectiveness of the choke by drawing a 30 inch circle around its densest part, count the number of holes inside the circle, divide that number by the average number of pellets in our shot shell, and state the pattern as a percentage. It is generally accepted that a full choke gun places 70% of its shot charge within the 30 inch circle, a modified choke gun places 60% of its pattern in the circle, an Improved Cylinder places 50% of its pattern in the 30 inch circle. These numbers are only approximations and many authorities allow leeway of + or - 5%.
Note that I said, "... we see that the shot pellets form a roughly circular pattern." What we see affects how we perceive the pattern. Since the paper is a flat, two-dimensional plane, most shooters probably give no thought to whether all the pellets hit the paper at the same time. In fact, the shot pattern is three dimensional and while it is round when viewed from the front or back, it is elliptical when viewed from the side. Thus, as a pattern of shot travels through the air in three dimensions, it is generally egg-shaped. Some commentators call it a "cloud of shot." All that the term "shot stringing" refers to is the elongation of the pattern of shot as it goes through the air.
The second matter to consider is how significant shot stringing is in the real world of the shotgunner. For reasons which I hope will become clear, I doubt that it matters a lot.
I preface the following comments by noting that a number of people have studied shot-stringing without reaching uniform conclusions. For example, it might seem logical that small bores and/or tight chokes should result in longer shot strings than large bores and open chokes. Some experimenters have reached this conclusion but others have determined that shot stringing occurs at approximately the same rate for all bores and chokes.
Shot stringing occurs because some pellets lose their velocity at a faster rate than other pellets. There are several reasons for this. One is that some pellets become deformed and have a poorer ballistic shape than others. Another reason which often is overlooked is that some pellets are bigger than others. This is because pellet size is not exact but is an average within manufacturing tolerances. As a rule of thumb, ordinary shot may be half a size smaller or larger than the average.
Just as a pattern gets wider as it gets farther from the gun, it also gets longer. Thus, just as a pattern is approximately twice as wide at 40 yards as it was at 20 yards, it also will be twice as long, and the pellets which were in front at 20 yards are still in front at 40 yards. That raises the necessary question, just how long does a pattern become? Without a long review of a lot of authorities who disagree with one another, I think that for working purposes we may safely assume that the effective part of a shot pattern lengthens about two inches for each yard of range. Thus, a 40 yard pattern would be about 80 inches long. That means that the first pellets to hit a pattern sheet are six feet, eight inches ahead of the last pellets to get there. That sounds like a lot until we consider that a 12 gauge express load of #6s pass through the pattern paper at an average velocity of 714 feet per second. The first pellet hits the paper going 717 fps and the last hits it going 711 fps. The lag-time between those two pellets is .0084 seconds.
Now that we have a lag-time factor, we can determine the effect of the shot stringing on a target. On a straight away target, one requiring no lead, the effect is nil. Both pellets hit the target exactly where they would hit on a paper. The greatest possible effect occurs on a 90 degree crossing target and the magnitude of the effect depends on the speed of the target. The average speed of a standard American clay target is approximately 50 feet per second. Such a target would move .42 feet or 5 inches in the time between the first and last pellet of the pattern pass by. Will that movement cause the target to dodge a pellet? Or will it cause the target to run into a pellet? The answer is that one is as likely as the other.
Now we get to the important part; look closely at your pattern sheet and find the pellet which hit first. Now, place your target there, move it five inches, and see how many other pellets will be in its space as the pattern passes.
Oh, you may have some problem with the last part of this experiment. Which pellet got there first? There is no practical way to tell, so place your target in any part of the pattern and move it five inches. Those are the pellets which will have a chance of hitting the target. You should find a lot pellets that more than likely would hit it.
And bear in mind that this is a "worst case scenario," any target that is crossing at a lesser angle than 90 degrees will move proportionately less until you get to the straightaway where the effect is nil.
Finally, since this is the 4-10 website, let us apply the foregoing analysis to the .410. When we do, things look proportionately a better. The reason is that the .410 is used at shorter ranges than 40 yards. It is about a 25 to 30 yard gun. At the shorter range, both the stringing of the pattern is less and the movement of the target is less. The stringing effect at 25 yards is only 25/40 or 5/8 as great as at 40 yards, and the amount of movement the target can make also will be reduced as the time is less.
In general, forget about shot stringing. You canít really do anything about it and it probably does not matter.