Is it possible to increase the speed of projectiles like a lot (to the point a bullet cant be seen ,unless in slow mo)?
Sadly, no. Contrarily to characters, projectiles don't have addressable attributes, apart from getting (not setting) their position. AFAIK, the only manipulation you can do on a projectile object is to play an FX on them or destroy it.
There also is no global constant for projectile speed we could use to affect every projectile.