A couple of thoughts when approaching this contest, which has suddenly become curious as to who can outspart the next guy...LOL!
1. Print out a full-size photo of the Bison to try out your ideas. Add sketched parts, re-arrange the elements, etc. It's in 2D, but it will help you re-imagineer the gun.
2. With the book(s) in hand, totally immerse yourself into the universe. My guess is the winner will be chosen not so much on the whiz-bang (pun intended) of the cleverness, but in how the look and feel elicits the "that's it" reaction to how it fits into this creative universe. There is a lot of heavy theming going on here, and "thinking 1900" will help make this happen for you.
3. This has nothing to do with looks, but I'm putting a beeper motor and small counterweight inside of it to simulate something "kattywampass" working inside. The photo captions in the book describe near-disaster and total toxicity when using this not-quite-proven technology that pre-dates the Titantic! I suppose a Bison "bursting into flames" could be an optional design?? (Who's up for a flame paint job on their "Buffalo Burger"?) LOL...
My designs are immersive and reversed engineered...although I'm not quite yet willing to divulge them. My thanks to WETA for their patience. Kinda reminds one of guessing how many gumballs are in a jar? i.e. how thick is the jar's glass? etc...
-Paul.