I'm not a big gun nut, but I'm looking for some details to add some flavor to the campaign. I guess the specific construction of IK guns has some interesting side effects in the way they are handled (or should be handled). So let's get a-thinkin'?
First of all, as far as I see it, the IK blast powder seems pretty great. Ignition by combining components eliminates the need for a percussive cap and thus one element of failure. Also, a single spark might burn through the paper coating of one component, but won't cause the round to go off unless it manages to hit right where the separating liner is.
It also seems pretty smokeless (compared to black powder). Don't know how bad fouling is. Cleaning up the breech seems part of loading it, but beyond that, residue seems pretty low.
As for the breech loading mechanism, pretty much everything seems to be break action, like a shotgun, right? I'm not so sure whether those huge top-mounted knobs actually make sense at all. You might as well put them on the side, and then could aim a lot better along the barrel. So let's add that to the artistic license pile, along with the insanely huge calibers.
The ignition is purely internal, so rain is probably not a big factor. Immersion in water is a different matter, of course.
Breech loading allows you to reload on the ground, so there's definitely more sniping and skirmish action going on than in e.g. Napoleonic warfare. Which seems to support Warmahordes
Now drawing back the firing pin seems a manual part of the loading action. Any safeties around, possibly blocking the exposed part of the pin somehow? If not, carrying around a loaded gun is basically safeties of (condition 0?). Military discipline could be against it, with soldiers only doing it if e.g. they're advancing ahead, expecting enemy contact at any moment. And some crazy gunslingers could carry their braces of pistols all ready to go, just to shave off a few precious moments.