If you're going to use case expansion for reading pressure, here's the method I suggest. Buy a large lot of factory ammo. Wait 6 mo. to a year to see if there are any recalls on that lot of ammo for pressure or other issues. Test a statistically significant sample of it in the test gun. Pull the bullets and primers from the remainder of the lot and use it for your own load development, again using a statistically significant sample size. This way you have a reference to a known safe standard. Make sense?