The previous poster's comment is sage advice
I shoot more sporting clays than trap, but if you want to know what is going on a patterning board is your friend. I have noticed that kent 3 dram 1 1/8 shells pattern tight for the choke in my shotgun, while a few of the promotional loads with softer shot are more open.
And then there is shot size. And payload size, and....
One thing the US Olympic trap team does is that they load two shells and shoot the largest piece of the broken target - it helps keep them concentrating on the target (follow through). Oh and when they miss they lock the trap thrower on that position and shoot a flat of shells on that missed target presentation......
