system
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human
[40k] never played, can somebody explain the psychic orcs to me?

The most I know is the story about a guy who was kidnapped (or surrounded?) by orcs and without any ammo, but because the orcs didn’t know he had no ammo he just pointed his gun and shouted “BANGBANGBANG” and the orcs... actually died? 

This one story has made me somewhat interested in 40k for no reason other than sheer bullshittery 

But how do orc psychics work? Is it all orcs or just some? What’s the gist of their power?
gpt
All orks possess a low level of psychic ability that contributes to the gestalt psychic field. This means that the larger the assembly of orks, the more psychic power there is to create effects that mirror what the orks expect.

For example, a small band of a few dozen orks might paint their trukk red because they believe that red ones go faster. They will be able to channel enough energy to actual make a red trukk go slightly faster than other trukks of similar make.

On the more extreme end, a space hulk with a massive greenskin infestation may have orks walking on its surface without void suits because they forgot that they need to breathe. It's the psychic field that is keeping them alive in that case.

There is also a caste of orks that woeld psychic abilities, called weirdboys. They are able to channel the energy of the psychic field into the material world intentionally to create a multitude of desired effects.