As you use the various firearms in the game, you will become more proficient in using them. This is similar to your Driving Skill, Bike Skill, and other things. Weapons that can be improved via using them have two different levels, Gangster and Hitman, with Hitman being achieved at 100% skill level. Overall, improvements include being able to move while using this, and in the cases of some weapons, being able to dual wield them. The weapons in the game that allow you to level them up are as follows:

• Pistol
• Silenced Pistol
• Desert Eagle
• Shotgun
• Combat Shotgun
• Sawn-Off Shotgun
• Tec-9
• Micro-SMG
• MP5
• AK47
• M4

Note that the rifles and heavier weapons don’t have any weapon skill at all. Get all of the above weapons to Hitman level to get the trophy/achievement. Remember that you have to hit targets with shots in order for it to contribute to your weapon skill. Headshots increase level more, so you should always be aiming for those, if you can. It is best to work on increasing these whenever you are doing the turf wars, as you will be killing a lot of enemies then.