Shot string is length of the pellet cloud measured from the very front pellet to the very last one as it moves through the air towards a target. A ton of people know about patterning and the concept behind it, but very few take the time learn about their shot string.
The easiest way to tell the differences between the two is patterning tells you where all the pellets are hitting, shot string tells you how long it takes for all the pellets to hit. Lets look a little deeper into the subject and see if your shot string is a problem and if you can improve your shot string.
Lets start with some of what affects your shot string- type of choke, pressures from firing and shot hardness/type of shot. Now all those factors determine the amount of deformation to the shot (shot that is no longer round like it was prior to firing). More shot deformation equals longer shot string, and that’s not good.
Type of Choke
If you run a cylinder bore (no choke) there is nothing at the end of the barrel for the shot to get forced through. If on the other hand you have a full choke, then the shot has to squeeze its way through the choke which can cause shot deformation and lengthen your shot string.
Pressures from firing
As the powder ignites and begins to propel the shot down the barrel with a massive amount of acceleration causing the shot at the back of the pack to get deformed (compressed) from the pressures.
Type of shot/hardness of the shot
This ties directly into the other 2 variables I talked about; soft shot will deform far more easily and affect your shot string. Take steel and tungsten iron pellets for example; they are significantly harder then lead and are not deformed by the rapid acceleration out of a gun barrel so you will have a better (shorter) shot string.
So how can you easily improve your shot string (and patterning)? Spend the extra change and get quality ammunition to use. Look for something that is made of hard shot (high antimony count), platted shot (copper or nickel) and steel shot. Try and avoid the cheap soft lead ones.The harder the shot= the less it will become deformed= the smaller the shot string and the better the pattern.
A quick, down and dirty way to compare shot deformation between types is to open up a shell and grab a couple pieces of shot, then grab some pliers (channel locks work great) and slowly squeeze the shot making note of how much pressure you used and how much it deforms. Then try the test on some other types and compare.