I did a lot of pattern testing loads in the 1970s. The most important factor turned out to be quality of shot (hardness and roundness) -- no surprise. Cu plating on really hard, round shot patterned about 5% tighter than the same shot without plating. With soft, irregular size and shape shot I could get at least one full decrease in nominal choke, sometimes two, from percentages same load did with quality shot. Soft shot, plated with Cu is still soft shot.
I also rediscovered the obvious fact that one needs to count the actual number of pellets in a load, not assume the nominal values given in tables.
I did find some loads that patterned tighter or looser, given the same shot. Another useful result was that above a certain volume of shot, the patterns got progressively thinner for my guns. This was 1 3/8 oz for normal 12s (70 and 76 mm chambers), 1 1/8 oz for 16 and 76 mm 20s. No surprise here either.
I also found some loads that gave more consistent pattern percentages than others, again, no surprise.
Size of shot did not have a consistent effect on pattern density, again, no surprise.
All this was quite usefull to me. It made my use of my guns with my reloads a much more predictable activity.
I still sometimes pattern my guns, especially ones new to me, mostly to determine how close POA and POI are for me. When I went back to waterfowling many years ago I patterned several loads with bismuth and Kent TM. Those "ugly" bismith pellets patterned quite tightly, almost independent of choke. The Kent TM behaved more like Pb alloy shot in the same guns.
Patterning is a highly recommended activity for shooters, with their loads in their guns. No more, no less.
Niklas
