Spreader and concentrator loads are about as old as choke boring. When considering such loads it is worthwhile to think on how patterns work. Each piece of shot follows a ballistic path based on the velocity and actual direction it is pointed at the point it is last influenced by other pieces of shot. We can consider that each piece of shot has a forward (direction the gun is pointed) velocity and a sideways velocity (90 degrees to the forward direction). The forward velocity is large and the sideways is small. Choke effect seems to be constrained to cylinder bore to full bore. To get more or less choke effect we must introduce something else into the shot load. Spreaders have been more effective than have been concentrators.
There are two more or less fundamental ways to spread the pattern. We have to have some way to inpart additional sideways velocity. Over shot wads have been maligned for "breaking up the pattern." Bingo! We add several over shot wads. However, the wads act outside the barrel and, thus, have a significant degree of randomness to the disruption they cause. The other way is to add a "post" within the shot column. the shot will pressurize the post during acceleration. As the shot clears the muzzle the post will depressurize and, thus, give back a degree of energy to the shot in the sideways direction. The shot will have an additional amount of sideways velocity. The post is much more controlled and much less random in how many and how much individual pellets are influenced.
DDA
