A unique appearing weapon, the SSP 90 has a 50 round clear magazine loaded into the top of the weapon. Its ballistic performance is vastly superior to the 9mm round. This weapon fires from a closed bolt which allows for perfect accuracy while firing semi auto. Its ergonomic design makes it easy and comfortable to fire and helps add to its deadly accuracy.
It is so far the only auxiliary weapon that has 50 rounds in each magazine.
In Syphon Filter: The Omega Strain, it shared ammunition with the SP 57. This is correct in real life as well. The SP 57 and SSP 90 are both based on real weapons made by FN, the Five-seveN and the P90, and both are chambered in 5.7x28mm, essentially a pistol-sized rifle round. Its ammunition is capable of penetrating Class IIA body armor.