My understanding is that you may get a small increase in velocity. One test that I did with a large amount of seating depth change only resulted in 20 fps or so increase, and it wasn't a straight line change, it would go up a bit, down a bit but it trended on the increase.
It may differ for each powder/bullet/primer/firearm, so get a large opinion sample.
The extremes are a different can of worms, if the c.o.a.l. gets the bullet into the lands or if bullet seating starts powder compression it can change a lot faster.
It may differ for each powder/bullet/primer/firearm, so get a large opinion sample.
The extremes are a different can of worms, if the c.o.a.l. gets the bullet into the lands or if bullet seating starts powder compression it can change a lot faster.