Now this is an interesting handgun, the Medusa M-47. Designed to chamber a majority of .30 caliber handgun rounds, the ejector has little fingers that double as extractors/shell holders for rimless cartridges.
There is plenty to support the notion of headspacing cartridges off an extractor, and several firearms that do so safely. But I have to imagine that with the Medusa M-47 that some of these cartidges won’t work nearly as well as others, because the case walls aren’t straight on most cartridges designed for semi-automatic handguns.
Sure, they’ll fire-form to the cylinder, but the bullet will travel un-guided until it reaches the forcing cone, at which point it may not be very ballistically stable. And even then, I’m sure there’s enough variation with bullet diameters that not every round will perform as well as they would in a gun designed to fire them.
Check out the full-size Medusa M-47 in action: