Because of having about 200 mag cases, and over 2000 S&W Long cases, and with the price of cases, not wanting to go out and spend a few hundred dollars to buy a couple thousand cases 1/10th of an inch longer than the cases I now have.
I can start with the 3.5 gr of Unique I have already used and work it up, but I thought maybe someone out there may have already done this.
This is the same reason for using 38 special cases for medium 357 mag loads. Case availability. In that case, the old timers such as Keith and Skelton had done the load work, and listed good using loads in their writings. In their time, it was 32-20 that filled the role of the 32 mag today, and they did list hot loads for that.
Thanks for taking the time to respond
Louie