What is the muder weapon for Agatha ABC murder?

The murder weapon in Agatha Christie's "The ABC Murders" is a .25 calibre automatic pistol.

The killer, Alexander Bonaparte Cust, uses this weapon to shoot his victims: Alice Ascher, Betty Barnard, and Sir Carmichael Clarke.

It's important to note that the weapon is never specifically named, but described as a "small automatic pistol" and later confirmed to be a ".25 calibre" in the book.