Are you speaking about what we see on page 3? I'm pretty sure those are cannons. The action lines make it look like some sort of gatling gun spinning, but we can see the cannon's large barrel opening in the recoil's "afterimage".
I wasn't expecting trench warfare in this world... it's an interesting comination: "classic jrpg-esque fantasy + attritional warfare". I hope I can find something to feel that niche.