Several reasons might cause CS 2 FPS drop randomly, such as network instability, computer performance, and items in the game. For instance, when your character in the game walks to a place full of utilities like smoke, grenades, and Molotov, your FPS is very likely to drop.

The easiest way to do this is to play on Deathmatch free-for-all, as you'll have plenty of targets to take out. Plus, if you play against bots, then any reasonably skilled human player will be able to get the kills easily. Once you've got the kill, just play out the match until the end and you'll get the achievement.

By double-tapping Q, you will swap between your last two used weapons. Similarly, pressing keys 3 and then 1 quickly would have the same effect, though that requires more of an effort.