>>542444405
Two of these happen to be explained in detail, a couple of the others are fairly straightforward gun designs.
Anyway, do MCH guns often have nonsensical or stupid designs? Absolutely, but they're all guns shooting bullets or slugs of various types. Yes, even the Allagan ones:
>These simple mechanisms, dating back to pre-imperial Third Astral Era, were powered by a powder of finely ground fire and wind crystals that would be ignited using a simple incan-tation of flame. The resulting explosion would cause air generated by the wind aether to rapidly expand, forcing a stone or metal projectile from the cannon’s barrel in the general direction it was pointed.

If it's doing "science-magic" to ignite something that accelerates a projectile after you pull the trigger, it's a gun, despite the weird or dumb design.
>>542445068
No problem. As frustrated and dispirited as I feel about the lore nowadays, I did waste a lot of time caring about it over the years, so I don't mind clarifying or explaining things like that.
>>542445542
Oda is not a good worldbuilder and cares very little about consistency. He also gives bullshit answers at Q&As just to pretend something was planned or connected all along, even if contradicts the game. The setting is carried by what Iwao established back in 1.0 and what others did with the story, though not even the latter can be relied upon anymore.