The problem for a pistol design is: how do you fit something like that in a regular grip, with big .44 Magnum rounds in it?
You don't, you have the magazine attach outside the pistol grip. Of course that makes it an illegal assault pistol in CA, so you can't have one.
That law effectively limits how powerful autoloaders can be since the cartridge length can only be so long while still working for most hands.
A unique magazine design that attached lengthwise or something similar could help keep the dimensions the same as a regular pistol for use with a holster etc.
Perhaps a pistol magazine that has a a few tubular stacks, or something similar to the way the p90 magazine operates, but attached on the bottom of the pistol lengthwise forward of the trigger guard. Or maybe even one designed to attach along the side of the pistol.
Once someone was used to such a design it would quick to load, but allow cartridges larger than what can be fit into the pistol's grip.
The grip itself could also be any size or shape you desire since rounds would not have to feed through it.
There is a few options for larger rounds, but all of the ones I can think of require a magazine that attaches outside the pistol grip.
As far as the OP's question,
a 9x25 dillon loaded light will use the same bullet as the .357 Magnum, and at the same velocity. So the round can be duplicated exactly.
It is normaly loaded quite a bit hotter than the .357 though.
