TECHNOID’SCOLUMN
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SHOT STRING OFTEN IN ERROR, NEVER IN DOUBT BY BRUCE BUCK
A
s shotgun shooters we are most accustomed to think of our shot patterns as two dimensional. We count the holes on a piece of paper inside a 30” circle at 40 yards and compare it to the total number of pellets in the load to come up with the choke effectiveness. We expect a Full choke to produce about a 70% pattern in a 30” circle at 40 yards, a Modified 60%, IC 50%, etc.
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And yes, we also know that the center of the pattern is denser than the outskirts. I am told that this is due to the demands of the Gaussian distribution but, to be honest, I slept through most of math class. Anyway, the result is that the pattern gets weaker as you move farther from the center. The problem with all this patterning stuff is that it is two dimensional and we live in a world with three physical dimensions: height, width and depth. Where is the depth dimension in these patterns? Does it matter? Enter the shot string. When the shot comes out of your barrel it doesn’t fly down the range in a flat sheet like it ends up on your
pattern paper. It comes out in a swarm with some shot in front and some trailing. The farther from the muzzle you go, the longer the shot string gets. At 40 yards, a shot string from a target shell can be six feet or a good bit longer. What causes the shot string? Pellet deformation mostly. Assuming that you start out with all the lead pellets in the shell being the same size and nice and round, that isn’t the way they leave the muzzle. The pellets have a rough journey down that barrel. First there is set-back. When the primer gets whacked and the powder goes off, the shot wad and the shot get a sudden violent push of around 10,000 pounds per
square inch. Physics being what it is, the shot at the back of the wad gets pushed first into the still stationary shot at the front of the wad. This puts a lot of pressure on the lead pellets— and the lead, being fairly soft, tends to deform. Some of the pellets get flattened a bit. There is more distortion when the shot enters the forcing cone from the cartridge and gets squeezed down to the bore. More abrupt forcing cones can increase distortion more than elongated cones if you listen to those who make a business out of lengthening cones. Not only do the pellets have to go through initial set-back and the
