Who, before you, described flip as that gun movement which occurs before the projectile(s) leave the barrel? Maybe you are assuming what others are confusing?
Isn't what's important the end result of all the forces at work? What does it matter what occurs before the projectile leaves the barrel or what happens the instant after?
Not trying to be argumentative, but rather to understand the point of the question. The question was, how big an issue it is for S x S shooters. What the end result of all the forces at work is, is what causes any effect on a shooter. Right?
SRH
