9x39mm PAB-9 is a type of rifle ammunition featured in the S.T.A.L.K.E.R. series.
The PAB-9 cartridge is a cheaper version of the SP-6 as the latter is expensive and difficult to manufacture. The PAB-9 used stamped metal penetrators rather than machined ones, the penetrator of the PAB-9 was larger and more exposed than that of the SP-6, and the PAB-9 had a flat nose to make it easier to feed from magazines. PAB-9 rounds performed worse due to cheaper materials used.
PAB-9 rounds have similar performance to the 5.45x39mm BP and 5.56x45mm AP rounds, with a fairly high penetration ability - making them invaluable against heavy armor. However, despite having superior air resistance, they tend to be fired at much lower velocities, making them ineffective at distances where the BP and AP rounds may perform better.
Shadow of Chernobyl
Duty and Monolith veterans and experts will likely be the player's best source of these rounds, as well as the rare and more powerful armor-piercing varieties. Spetsnaz operatives deployed in Pripyat carry these rounds as well. The Barkeep and Sakharov will also begin selling 9x39mm rounds after the player's deactivated the emitter in Yantar, although typically in small quantities, and not too often until the player deactivates the Brain Scorcher itself. They tend to be found in stashes (Backpack with the loot, Secret stash in the bus in Yantar), as well as any outposts held by the Monolith, particularly within Pripyat. Colonel Petrenko will commonly sell them.
9x39 caliber rounds are more available in Clear Sky, as the Spetsnaz, Duty, and the Monolith are not the only factions to use them. Some Loners and Renegades equip 9x39mm rounds, the latter equips them later in the game. This ensures that the player can acquire 9x39mm rounds without too much trouble, although they generall come in small quantities. Mitay, Sakharov, and the Duty trader in the Red Forest may sell these rounds in small quantities.
Call of Pripyat
Though 9x39mm caliber ammunition is not at all uncommon in Call of Pripyat, officially PAB-9 ammunition is not available in the game. The "low-level" 9x39mm ammunition is the 9x39mm SP-5 round; however, its overall statistics are almost identical to PAB-9 rounds from previous S.T.A.L.K.E.R. games, and internally the ammunition is still treated as PAB-9 ammunition, to the degree that it uses the PAB-9 object name, inventory icon, and model.
In real life, the PAB-9 was made to be a low-cost substitute for the SP-6 round, using a stamped rather than machined steel core bullet. The bullet ended up being so poorly performing that it was withdrawn from use shortly after and is no longer made.