Rob,
You are asking the right questions.
The problem is with the ammunition makers. They think the entire market is driven by muzzle velocity. So as the payload changes, they tinker with the powder, charge weights, etc to get the mv to hit the magic 1200fps. You are correct, you will not find many listing pressures, but again they are quick to print the velocity on the box.
As Rocketman pointed out, they have to produce a shell that will cycle those semi-autos. That is where the dollars are being spent.
Pete
