Seating depth…what does it do?

[Doom]

It’s interesting that predicated pressure and predicted velocity decrease and increase with seating changes that suggest a point of impact shift on the target and a chronograph variations beyond the normal ES but why do we not see it on the target ?

Not sure how Boyd stumbled into this thread! But if I may propose something here to explain what you have observed. When you consider short range accuracy (100-200yd) the requirement for accuracy is not a strong function of velocity. In fact the BC of the bullet or a 100 fps variation in muzzle velocity as a very small affect (you can verify with a ballistic calculator). What determines the final point of impact is the direction the bullet is traveling when it leaves the barrel and various effects of random dispersion. Probably the largest factor in quality components and barrels becomes consistent in the barrel pointing, hence vibrational effects. However those velocity variations that are negligible at 200 yds become increasingly significant as the range increases. At some point they become the determining factor in the dispersion.