Originally Posted by boomtube
You aren't "crazy" but you're missing a part of the puzzle when you isolate and measure the height of a new primer; they don't stay that high. Observe the profile of a new primer and you will see that the anvil legs are proud of the cup edge by a few thou, that make's transporting and handling them a bit safer. There is no standard height for new primers, the makers can use all the anvil height they wish.
When we seat them - properly - the cup will bottom in the primer pocket, forcing the anvil in to slighly compress the priming pellet and increase firing pin sensitivity.
So, you're thinking but you need to fully seat the primers and THEN measure the cap height; it should be 3-4 thou below flush, you will probably be fine. If not, THEN it may be time to use a bit more seating pressure OR a pocket uniformer.
Your velocity spread probably came from a slightly low ignition temp for the type/volume of powder you're using, not the height difference. All powders burn most consistant in a proper peak pressure range and cooler primers may not get it up to where the burn will be good.
You are absolutely right boomtube. I measured a new primer, primed a case, decapped it, and remeasured it and sure enough, it shrunk by about 2 thou. My pockets still seem to be a little shallow though. I may just try to uniform the pockets to get them to seat below flush. Thanks for the advise.