Bob, I have Brister's book but don't have access to it at the moment. I'll try to remember to check and post better answers when I can.

I read it years ago, here's what I remember. I could well be wrong on some of this. First, shot strings were increased with fuller chokes (no surprise but exactly when you don't want longer strings). Some were longer than most in this discussion -- I'm stretching but I think some were up to around 12 feet. Soft shot is definitely a handicap, and was a prevalent problem when Brister wrote the book, in the late '70s.

Incidentally his greatest interest / concern was (appropriately) waterfowl loads, so he worked at some ranges beyond 40. Also, most ducks fly at speeds closer to 50 to 60 mph, rather than 30.

Fred