The 9mm Pistol is not particularly effective against multiple targets, and better when facing off against one or two targets at a time. When engaged in a firefight using the 9mm Pistol, aiming at the target's head is advised. Aiming for the body is not very effective, especially not if the target is wearing body armor, and it can take up to seven shots at medium range to score a kill. On the other hand, it normally takes only two headshots to kill.
The 9mm Pistol's recoil makes it difficult to quickly fire the gun while retaining any accuracy past short range. Instead, one shot should be fired at a time to hit enemies at medium to long range.
The 9mm Pistol is significantly more accurate than the MP7 and does a little more damage, making it convenient as a backup weapon if the other weapons are running low on ammo.
Ammunition is plentiful in the early chapters while battling Metrocops in the Canals, but it becomes slightly harder to come by in later chapters, where it is usually only found in some supply crates and abandoned outposts.
Both Metrocops and Overwatch Soldiers can be killed by a single shot if they are unaware of the player's presence, even in Hard mode.
Although the 9mm Pistol lacks considerable stopping power, it has a high rate of fire (as fast as the trigger can be pulled) and a sizable 18-round magazine. It is a useful all-rounder and is particularly effective against weak or slow enemies, such as Metrocops, Headcrabs, Barnacles, Zombies and Scanners.
The 9mm Pistol is one of only two ranged weapons that can be used underwater, the other being the crossbow.
When the 9mm Pistol is fired by the player, no spent cartridge casings are ejected, while it does when fired by an NPC.
Before the May 26, 2010 update applied to Half-Life 2 and Episode One, players could hold down the secondary and primary fire to "charge" their next shot (it would fire several shots at once at the same angle, essentially creating one extremely powerful shot).