Welcome to Librarium Online!
I just had a random thought pop into my head, as they often do, if I have a Zoan that I want to do a powered up shot and fail the test could I then still do my regular shot?
basically can I always shoot but the test only determines whether it is strong or not. I mean basicly one is a psychic attack and the other is just a gun for all intents right?
how would it work if say a marine had a psychic shot and failed could he then shoot his pistol?
No. Unless otherwise specified a unit may only use one shooting (including psychic shooting) attacks and may only use a number a psychic powers specified (but only one psychic shooting attack, can't use it twice). If they fail the psychic test, they can't shoot. Same goes for a SM Librarian.
Thats basicly what i thought just wondered how shooting/psychic attacks worked together
More specifically see page 50 in the main rulebook under 'Psychic Shooting Attacks'
I'm not sure what you are talking about. Zoantropes have two psychic powers that happen to be psychic shooting attacks, they have no "regular" shooting power.
As for psychic shooting attacks and regular shooting attacks, most models may only perform one shooting attack per turn, it doesn't matter if it's psychic or not, you only get one shooting attack. Some models can go around this, like the Hive Tyrant, since it is a Monstrous Creature it may fire two shooting attacks per turn, so it can shoot two Heavy Venom Cannons, or one Heavy Venom Cannon and use one psychic shooting attack like Leech Essence.
The opponents that have the hardest time accepting this are Space Wolf Players trying to use their Rune Priests for several psychic shooting attacks like Living Lightning and Jaws of the World Wolf. Arguably they may use two psychic powers per turn, but they may only shoot once, so it's either Jaws of the World Wold or Living Lightning or their Bolt Pistol. They can however use one psychic shooting attack like Living Lightning followed by another psychic power that isn't a psychic shooting attack like Tempest's Wrath (if he is upgraded to Master of the Runes that is).
Another good example is Eldrad Ulthran who may use 3 psychic powers each turn, and can even cast the same one twice is he so wishes. But he still can't use Mind War more than once since that is a psychic shooting attack and he may not fire another weapon. But he can do a Mind War followed by Doom and Fortune for example since the latter two are not psychic shooting attacks.