Commonality! I try to ingrain that in new Shooters/Gun Owners go with a 9mm x19. Ammo is commonly available for purchase and if/When the SHTF 9 will be readily available for “pickup” after dispatching the enemy. It’s common Worldwide. And a lot of LEO uses .40 and the zer0 and ilk Ordered/Purchased a Gabillion Rounds to hand out to NWS/Library/Smithsonian/FDA/NOAA/DHS/DOE(Energy)/DOE(Edumakashun) and all the others. As well a .223 IIRC.
Of course I’m very particular about the .45. It feels like part of My hand just like the old Ruger P85MK-II.
Another I like as long as it’s possible to stay in place is .44 Magnum in a Ruger Blackhawk and a Lever Action Winchester to take on the Heavy work. Not good for “Mobile” due to bulk weight on the big Caliber.
.22 for on the super mobile with a good Rifle for sniping& Dinner and a Pistol for PDW at Close range. Some people don’t think much of a .22, until I remind Then a .22 almost killed President Reagan with a flailing long shot that hit the door jamb and entered.
Ruger,
RUGER P85,
Talk about That One!