Psybolt Ammunition, better known simply as psybolts, are silver-tipped, psychically-charged Bolter shells, used in Storm Bolters and similar Bolter weapons. Psybolts are the favoured ammunition used by the Grey Knights Space Marines.
When fired, each bolt can be imbued with a portion of a Grey Knight's innate psychic power, causing it to glow with an eerie blue light and strike home with significantly greater force than an ordinary bolt of its type.
Psybolts are difficult to produce and incredibly wearing on a Bolter's inner mechanisms.
But psybolts provide the Grey Knights with a relatively straightforward method of enhancing the power of standard pattern weaponry without resorting to the need to extensively retrofit the weapon itself.
- Codex: Grey Knights (5th Edition), pg. 62