Somehow, reading Warhammer 4000K
I assume you mean Warhammer 40k, unless ive not played it in so long that its up to 4000k
Anyway onto the system. While in theory it works relatively fine, my issues come up when trying to place it in a world and look at it in perspective. I may make a lot of assumptions along the way so feel free point out when I make an error.
1)From your description it seems like magic is not innate specifically to people, but is something that can be learned by most people (when you describe it being taught from books)
2)It is understood to be intrinsically dangerous, even under ideal conditions (i.e it’s a roll of the dice if at the end of your magic spell you’re gonna blow up or not, and this chance can only be lessened, never completely avoided)
3)It is dangerous to bystanders. (Sure you could just electrocute yourself, but you could also cause a lightning bolt to wipe out 5 square miles of civilization)
These three things lead me to believe that if this was the way magic worked then the practice of magic would quickly become forbidden by people not sanctioned by a ruling class. Much in the same way the world as a whole likes to control who has nuclear weapons.
I have no suggestion how to fix this, or even if it needs to be fixed, as I don’t know much about Full-Auto. If it’s the type of system/world where exploding-fiery death is as common as a rainy day, then this makes perfect sense. If that’s not what you’re going for then let’s see what might happen if we take out one of my three assumptions.
1) If not everyone can learn magic then you have a whole class of people who get persecuted for being walking time bombs. The world is also slightly safer because in general this population would be smaller than those that wouldn’t use it
2) If you get rid of it being dangerous, well then you’ve compromised your design goal so we won’t bother removing this one
3) If you make it less dangerous to use for people not involved (not in a direct way anyway, just so that a miss cast spell doesn’t result in widespread death for everyone, or at least make this the rare thing) then you get a whole class of people who are seen as nuts, or brave, or something else depending on cultural views of self-sacrifice and their use of a dangerous art.
As a whole I like the idea behind this system, I just think when something is this dangerous, it has wider reaching cultural effects and would be interested in seeing how the interior outsiders of magic view the art.