The Malleus Psycannon is a heavy bolt weapon that can get a damage boost when used by a psyker. However when looking through the various advance schemes, I only found two ways for a psyker to be trained in the use of one:
- Become an interrogator and use a wild talent to take heavy weapon training (Bolt)
- An elite advance.
Is there any other way that I missed ?
First, Malleus Psycannon is, primarilly an Astartes Grey Knights' weapon. 
That's for the fluff.
Concerning using one, in a DH game, remember that not only Imperial Psykers can be actual psykers.
Adepts can buy Psy Rating.
Any Carreer other than Imperial Psyker or Techpriest can become Nascent Psyker.
Any Carreer other than Imperial Psyker, Sororitas or Techpriest can buy the background package Wyrd.
So, unless you're a Techpriest, you can be a psyker. 
For example, you can be an Imperial Guard Wyrd or Nascent Psyker, buy Heavy Weapon Training (Bolt), take the Transition Package The Mind's Eye Open and become Interrogator (taking the Ascended Trait The Psyker's Gift), Inquisitor (idem Interrogator) or, even, Psyker Primaris.
DarkLoic said:
First, Malleus Psycannon is, primarilly an Astartes Grey Knights' weapon.
That's for the fluff.
Concerning using one, in a DH game, remember that not only Imperial Psykers can be actual psykers.
Adepts can buy Psy Rating.
Any Carreer other than Imperial Psyker or Techpriest can become Nascent Psyker.
Any Carreer other than Imperial Psyker, Sororitas or Techpriest can buy the background package Wyrd.
So, unless you're a Techpriest, you can be a psyker.
For example, you can be an Imperial Guard Wyrd or Nascent Psyker, buy Heavy Weapon Training (Bolt), take the Transition Package The Mind's Eye Open and become Interrogator (taking the Ascended Trait The Psyker's Gift), Inquisitor (idem Interrogator) or, even, Psyker Primaris.
I checked through the Adept advances, nothing there. Nascent is an elite advance and I thought Wyrd was as well, but it's a background package.
As for it being an Astartes weapon, wouldn't our PCs be getting one scaled down for human use ?
Or is it only a rifle sized weapon for the Grey Knights ?
I checked through the Adept advances, nothing there. Nascent is an elite advance and I thought Wyrd was as well, but it's a background package.
Um... yes, Adepts going for Loremaster can get Psy Rating.
Other than that, considering the Psycannon is a weapon commonly used by Inquisitors, I'd consider Psyker -> Interrogator -> Wild Talent an entirely appropriate route.
Cifer said:
I checked through the Adept advances, nothing there. Nascent is an elite advance and I thought Wyrd was as well, but it's a background package.
Um... yes, Adepts going for Loremaster can get Psy Rating.
Other than that, considering the Psycannon is a weapon commonly used by Inquisitors, I'd consider Psyker -> Interrogator -> Wild Talent an entirely appropriate route.
What I meant was that while adepts can get psy ratings, there is no way for them to train in heavy bolters.
Bilateralrope said:
What I meant was that while adepts can get psy ratings, there is no way for them to train in heavy bolters.
Sure is. Elite Advances; just convince the GM why you need to take it and haggle over the cost.
-=Brother Praetus=-
Bilateralrope said:
As for it being an Astartes weapon, wouldn't our PCs be getting one scaled down for human use ?
Or is it only a rifle sized weapon for the Grey Knights ?
As Cifer said, Ordo Malleus' Inquisitors are known to use some.
So it seems that some normal human size ones are avaible, in fact.
But, IMHO, psycannon are only avaible for highly trained individuals.
That's why it's a bolt heavy weapon, by the rules.
So, as I advised before, if you want to use one, you would better use a "military" Career Wyrd or Nascent Psyker than the Imperial Psyker one.
Or ask your GM to let you buy an Elite Advance, of course !