Seating force reflects the friction in the neck, and is a measurement of that. It does not directly reflect the "grip" or tension on a static bullet in the neck. There is no commercially available method or tool to measure the hoop tension of the neck.
Does the bullet, when the cartridge is fired, slide out of the neck while maintaining contact with the inside of the neck? Or does bullet release from the neck occur before any movement of the bullet out of the neck? It's an interesting question.
In my testing I have never been able to find a correlation between seating force and projectile velocity or impact on the target. But your experience may be different.
Finally, someone who understands the 2 frictional forces!!
Kinetic Friction, (frictional forces between two bodies in motion), and Static friction(frictional force between 2 bodies at rest, velocity=0). Static Friction > and/or = Kinetic Friction!!
"PHYSICS IS BASED ON PRINCIPLES, NOT ANALOGY", ELON MUSK!!!!!
HOWEVER, I disagree with the statement that Static Friction can not be measured!! As an Industrial Physist, with 105 credit hours of Pure Science, It can be determined with the OPs equipment!!
The Static Friction can be determined by stopping the seating depth a few thousands shy of the desired seating depth!! At that point, all motion is zero or STATIC!! Readjust the seating die to the desired depth and use the load cell data recording the Static BREAKING Forces (Static forces are the Static Tension Force in the neck which is equal to the opposing Static Compression Force of the bullet). YES, you have to use BASIC PRINCIPLES, also called the FUNDAMENTALS of Physics using Newton's Laws of Motion!! These Fundamentals are:
Bodies at rest, tends to stay at rest, unless a force acts on those bodies!! The Static State!!
For Every Force, there is an equal but opposite Force!! The Tension Force = the negative of the opposing Compression Force! Thus the 2 forces are balanced or Static!!
An understanding of Principles of Pysics leads me to a conclusion!! The uniformity of the Breaking Force is more Critical to Accuracy than uniformity of Seating Force!!! Another Fundamental of Physics and Engineering!!
STATIC FRICTION IS GREATER THAN OR EQUAL TO KINETIC FRICTION!!! In other words, who cares about kinetic friction once the static friction is over come by the accelerating pressure buildup behind the accelerating bullet which is now in motion or DYNAMIC!!!
Anyone opposing these Basic Principles does not understand them, and will argue using Analogies!!!