At first Norma would provide reamers to qualified gunsmiths for re-chambering. This was even before production ammo was available. They wanted to insure a market when the ammo was produced a year later.

I believe the Norma reamer had a long throat almost a free bore to it. This could explain the higher charges with lower pressure between the two cases. As noted above with custom reamers no telling what the throat length could be or even the no throat chamber.

"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli