A very good 30 cal can (like the SAS titanium Arbiter) will do the 300 BLK proud with jacketed bullets. If you want to shoot cast as well as jacketed projectiles you might consider a good user serviceable 9mm can like the TiRant or the Octane-9.
Am using an Arbiter now and am adding an Octane-9 for cast bullets when the F4 clears. Obviously have multiple uses for the 9mm can.
It is my understanding that these pistol cans won't stand up to supersonic rounds. i don't want to have to worry about whether someone made a mistake giving me a supersonic round by mistake. i want soemthing rated for supersonic. I see your point though. I plan to have a dedicated rifle and pistol can in the future so thats why i am trying to plan this out.