It only happens when Im not aiming and it happens with every weapon of the mod.

I do have some some mods (including optifine) and the conquest texture pack.
Do someone know why does this happens?

Please stick to the issue template.
I need to know what version of Flan's Mod and Forge you are using.

Try removing Optifine and any other mods as well as the resource pack to eliminate external factors.
I will re-open the ticket once you've done this.

It seems that the conquest reforged mod was the responsible of the visual bug since it changes the default crosshair of minecraft.