choke would be figured from the percentage-
but shot sizes pattern differently - so it would make sense for someone to require the pattern figured with their favorite size
this Chart has American size 7 in it
http://www.hallowellco.com/shot_size_chart.htm
percentages given by O'Connor
Full Choke: 70% or higher
Improved Modified: 65%
Modified: 55-60%
Skeet No. 2: 55-60%
Quarter Choke: 50%
Improved Cylinder: 45%
Skeet No. 1: 35-40%
Cylinder: 35-40%