Instead of using particle textures for bullets, use a slightly colourised distortion effect as a selectable option. As this would probably slow some computers down, you'd want the option of using textures.
I'm suggesting this as I think it would make the weapons seem more powerful, at the moment some weapons, like the shotgun, give the impression that you're trying to shoot people with cardboard...
A continuous fire option for weapons. This would, instead of shooting multiple particles, just shoot one particle that stretches the range of the weapon, is continuously relocated to the aim of the player and whose hitbox is continuously moved with the aim of the player. Used to create continuous beam weapons(like a Tesla coil/cannon).
Also, as a side note, love the new Pistol model...
This is only my opinion and I mean no harm by it...