Good questions!
Scales are available that will weigh within a small fraction of an ounce. MY experiments say most shooters can detect a 4 ounce change in weight; thus, 1 ounce accuracy is acceptable. Balance point is detectable for most at 1/4" variation and can be measured to a smaller fraction. Saying mounted swing effort is "near" the butt does not account for the distance from mount point to spinal axis (the real axis of rotation). Ignoring spine to shoulder width means we will not be able to have an absolute number, but the gun's contribution is captured.
Q#2 - Yes. However, the point of balance is the point of rotation that requires the minimum force to accelerate rotation. Note that an object "flung" through the air will rotate about its balance point. Most shooters will rotate the gun held between the hands very near to balance point.
Q#3 - For each shooter there is a set of stock measurements that will make for the highest % of successful shots. However, purpose of the shot may well require differing sets of dimensions; skeet gun vs trap gun. Like wise, sets of dynamic factors will/may vary for differing shot purposes.
DDA
