Symbolism, Imagery, Allegory
To say that the Gun Club loves cannons is pretty much the understatement of the century. To start, Maston calls cannons "the most startling manifestation of human power, which it sums up in its entirety" (7.13). He one-ups himself a few paragraphs later, referring to them as "the great criterion of terrestrial velocity" (7.15)—whatever that means. Clearly, the Gun Club sees the cannon as an impressive piece of technology (which it is) while neglecting to mention its actual purpose.
Well, we certainly know the purpose of cannons. When all is said and done, each member of the Gun Club is responsible for the death of roughly "2,375 men and a fraction" (1.11). That's a lot. What matters to the story, then, is that the Gun Club is so in love with the power of their technology that they don't think about its consequences. Maybe this moon mission is their way of choosing a different path for the club—but we doubt it. As Maston frequently notes, they'd gladly go back to producing weapons of mass destruction if only they could find a war to jump into.
In this way, cannons come to represent the hypocrisy of the Gun Club. Like Einstein working on the Manhattan Project, they become so infatuated with technology itself that they don't realize the harm they're doing. Oops.