45 Auto
I have a Remington Rand 1911 A1 to go with my M1 rifles and carbines, 03 and 03A3 Springfields, and a few other toys. Not much good having only one of the family and leving out the siblings.
I love the 45 and it's going on 102 years old. How do you improve on something that works that well.
John Browning developed it in 1905 and the US Government adopted it in 1911. One of the strangest guns Browning designed had to be the Colt Potato Digger machine gun.