Agreed Its a great way to experimentRegardless of 9mm ammo cost there's other reasons to make your own.
Want a powder puff SWC load?
Long ago, we tried to discover the barest minimum charge to cycle a 1911
We also wanted to see if we could make rounds that would just clear the barrel and others that were slow enough for us to see in flight.
We hammered a lot of bullets out of barrels