The trainer sometimes just "bings" at first start, then I qiut, start again with the game, and works. Another problem is, the infinite ammo disturbs the weapon. The machine gun can fire only 1-shots, but it has to shoot continually (not the police rifle). Rais's unique pistol is basically burst shooter. Bum-bum-bum. 3 shots per click. But with the infinite ammo it shoots only 1 bullet per click, because it "reloads" itself always. I have 99 ammo, I shoot, I have immediatelly 0 ammo, the 99 ammo appears again. So ALL of the 99 ammo disappears with 1 shoot, then appears after shoot.
(Spoiler: Rais's personel pistol can be found during a side quest from the hippie guy in the Old Town, where the loud music comes, near the library)