Editing Force Weapons

Psychic weapons are usually ordinary weapons instilled with a fragment of a psykers mind power. Thus, stronger pyskers make stronger psychic weapons. Psychic weapons use the warp to simply tear past any armour in existence, with only invulnerable saves standing against a hit from a weapon of this power.

Most psychic weapons can only be wielded by a pysker, as the power in them will burn out a lesser beings mind. Psychic weapons are simply so different to ordinary weapons that they are only able to be wielded by highly trained individuals. Mechanical devices are simply unable to utilize their potential, and non-trained wielders will die as a thousand tendrils of pyskic energy mind rape them to death. 

The only army that uses pyshic weapons as near standard issue equipment pieces are the grey knights. Also they can have ranged pyskic weapons, which is quite a lore-rape when you think about it. Because a psyker has to use a fragment of his mind to power weapons like this, it makes sense to make that weapon a reusable item, like a sword. Powering hundreds of bullets with your power would be tedious and sapping, and rather pointless. Thus the only time when a pyskic weapon is ranged is when mat ward shits on his keyboard.