The Beretta 418 was an unmitigated piece of shit. A .22 is a far better killer than a .25 ACP. The most worthless cartridge out of any in production. The Walther in .32 isn't much better. Fleming knew absolutely nothing about firearms, you can tell it from reading the Bond novels.
Rule#1: If you must get in a gunfight with only a pistol, make sure the caliber starts with the number "4".
The Beretta 418 is also known as the favorite pistol of James Bond. In the James Bond novels his pistol is described as having a skeleton grip (i.e. grips removed - frame only), and either a threaded barrel to support a silencer or completely sawed off barrel. It was his weapon of choice up until the novel and theatric adaption of Dr. No when a Major Boothroyd, introduced as "the greatest small-arms expert in the world", insists it be replaced by the Walther PPK. In reality Ian Flemming received a fan letter in 1957 from Geoffrey Boothroyd, a Bond enthusiast and gun expert, criticizing the choice of firearm for Bond calling it "a lady's gun" and suggesting several alternatives, among which were the PPK.