We did not have to re-invent the wheel on shotgun shell ballistics – we just had to buy the book with the eponymously succinct title of :
Shotshells & Ballistics: Ballistic Data Out to 70 Yards for Shotshells from .410-, 28-,24-, 20-, 16-,12- and 10-Gauge for over 1,600 Different Loads and 22 Manufacturers
Catchy eh ? War & Peace, it ain’t, but what John Taylor does not know about shotgun ballistics is not worth fooling with. It will enlighten you as to which cartridge is right for any particular use. Different horses for different courses.
So, in order to calculate the ballistically correct lead out to 70 yards, we just pick a shotgun shell – 2 3/4″ #8 – and get the elapsed time to the intercept point. That’s when the shot string hits. What it looks like comes from Dr AC Jones work on shotgun patterns: