Definately sold on the cannons Djinn, it's something I've been wondering about, like, it's a ship game without cannon balls, it just struck me as very odd, definately something I'd love to see.
Also this game is pretty much WWI-WWII era, mostly dieselpunk if I may, the tanks in Paritus display a higher tech level than a regular WWI setting, especially considering what real WWI tanks looked like. I'd guess Tesla Tech would be a very good start for a mid range fire based weapon ( electricity -> heat -> fire ) that could probably use a cooling mechanic instead of a magazine, possibly with a penalty incurred to the gun if you over heat it, like taking damage overtime, which would create some awesome risk/reward posibilities! (for example, keep the gun overheating and do some extra damage and possibly finish the job or let it cool and have more for later with a healthier gun?) Gun could also not do much damage or have a high ingnition chance, but could have a chance to kick people off guns for example (say a small chance so it doesn't become too much of an issue, but that's something for a balance thread)
I've had an idea of possibly chaining the electricity on multiple components if they are close enough, meh, dunno.
We could have a missile based artillery gun pumped up with napalm (since we are going on the fire based theme) that could have an ability to instantly overheat any gun it hit directly (not with the AoE, but on top of the regular fire chances), missiles would have to travel at a reasonable speed of course, if it's single shot it should be perfectly accurate of course, if multi-warhead, have some slight spread, but still limited ammo mag, could deal a bit of fire and a bit explosive, but nothing TOO much on the explosive part, fire damage should be high though.
When it comes to medium guns having piercing, I'm much in favor of auto-cannons and not machine-guns, so we can use projectiles and have a considerable skill floor for them to be used as to not to be too easy. Pom-Pom cannons could fit that role easily while lookin' good as well.
Liking the Light beam gun as well, I think Muse already has a model designed for such a gun.