The 9mm and 40mm are the most common design that police officers and even some civilians buy as their first handgun. The 9mm pistol is much of an older design than the 40mm. The 9mm was designed in 1901 and was released to the public in 1902 while the 40mm was released in 1990. the 9mm pistol is widely available around the world while the 40mm is restricted to the United States. Due to this, the 9mm has more sales than the 40mm.
The ammunition of the 9mm is also way cheaper than the 40mm because of the low cost of materials and the cost of manufacturing them. The 40mm has a bigger caliber than the 9mm thus, can penetrate a little further than the 9mm.
Those who have always loved guns will have no problem trying to figure out the difference between the two. The .40 will have a heavier cartridge as compared to the round of the 9mm. Since the .40 is known to be more substantial, this will also tend to be slower as compared to the 9mm.
Another main difference between the two is that the 9mm is known to be better and widely used all around the globe as compared to the .40. Those who do not know much about guns may think that the .40 is more potent because of its weight, but the truth is that it is not.