After beating them you will have obtained the next 6 weapons. The next step is to complete the side missions that should all be playable at this point since the story is now complete. After you have completed the main storyline you will have obtained 19 of the weapons. One is by completing the main storyline of the game. You will obtain these weapons in 4 different ways.
You will need to collect 14 Primary Weapons, 10 Secondary Weapons, & 10 Sidearms in order to obtain all the weapons. These areas are Mining Site, Village, and the Dam. There area a total of 34 weapons that you will need to collect throughout the three areas of Sniper Ghost Warrior 3.