Pawpaw suggested that I could tighten up the patterns a few different ways, primarily by buffering the shot and by delaying the wad opening up.
First I baselined the 17 grain Red Dot load (Federal hulls and appropriate wads) with 9 Single-ought buck. This load generated a 6" pattern at 30 feet with 25 grains of Unique out of the Mossberg, 24" slug gun. The Red Dot load is a lower pressure, softer shooting load and I thought it might tighten up the group because it would not deform the shot as much.
I was wrong. The 17 grain Red Dot load was also a 6" pattern. There may be a difference in how much the shot was deformed but it did not show up in how it patterned at 30 feet.
Then I reloaded a ""buffered" load. Buffering accomplishes two things. It supports the individual shot so they don't mash together as much as they experience max pressure. It also reduces the shot column's permeability to air. Conceptually, part of the physics that causes the shot to separate is the air that rushes into the crevices between the individual balls and pushes them apart.
I used granulated sugar as the buffer for this experiment. It is what I had, flows well, is non-corrosive and it makes the meat taste sweeter.
Those loads patterned 4" at 30 feet.
Then I tried a combination of buffered load and two wraps of tape around the petals of the wad. That load patterned 3" at 30 feet.
|Hole circled in blue is a double.|
Pawpaw was right
Buffering and wads can tighten up the pattern to an amazing degree.
I will keep loading the unbuffered loads because 30 feet is the maximum distance I envision during home defense and a 6" pattern is about perfect. If I had to stretch out the distance to 90 feet (30 yards) I would certainly look at unslit wads and some form of buffering. Going to a tighter choke would also be an option if tighter grouping of buckshot was my goal.
I will leave the barrel as it is, a straight cylinder. It shoots Foster slugs with competence out to 80 yards and it is the ERJ family's back-up deer gun.