To me personally, that would make about as much sense as doing all of the tests in one gun and then expecting them to work in another one.
You don't say what the round/case/caliber is but the case volume in a pre-fireformed case is different from a fully formed case, and pressure is probably going to be very different because you typically fireform with a slightly reduced load. Then when you have the fireformed cases you are probably going to try and load to an increased pressure/velocity. Isn't the increase the reason for the larger case or are you just wanting to improve a case design and still shoot what would be the same ballistic load in the improved case?
When I fireform cases I have fun and get in some long range practice but to each his own.

Then I use the newly formed cases and do the load workup.
