I think rather than straight increases or decreases in muzzle velocities related to seating depths picked up by chronograph or radar, it would be that you might see inconsistent readings. More so with reduced OAL rounds, and mainly with semi auto firearms. From my experience, if I went a little to far with a charge or short OAL, I\’ve seen fluctuations in velocities before flattened primers (and way before primer flow). I think another contributing factor has been case and primer brand but even more so is how many times that case has been reloaded as pockets may start to loosen. For clarity, these things I found were when working up 10mm loads in a pretty robust Springfield 1911, but the basic physics should still apply. I only mention it because with the 9mm work up, I\’m not really trying to \”Hot-Rod\” them so much as have reliable consistent performance. With the 10mm, I am looking to squeeze every last bit out of it but still run safe enough that I wouldn\’t hesitate letting my wife or kids handle it. (before anyone has a melt down, my \”kids\” are 28 and 32 years old)
Safe and happy shooting!