he can simply remove the air from the chamber remotely and the reason I don't affect the humans with the vacuum directly, is because magic is involved, if one character is using magic so can his enemies, so they are strengthened and would not be affected by a vacuum like a normal human would...
I'm writing a novel and wanted to research a possible weapon I came up with to make sure the physics are at least possible. However, I could not find anything on vacuum-based projectiles other than ping-pong balls, while this is interesting, but it doesn't answer my question on what would happen...