Okay so maybe I am asking for this at the wrong forum but please help,
Just for some context, we are playing a Homebrew Campaign of a setting based on the mobile game Granblue Fantasy, we are all playing Homebrew chars and I am playing the Witcher class as indicated here: https://docs.google.com/document/d/1oqys8fAJ_GTxbC7T2lsx_R9zqRsyo3R4W0E2NJ4 eAMc/edit?usp=sharing
Long story short we found out that there are crystals in the world that store and pulsate magical energy, so I asked our DM if he would allow me that if I come into posession of said crystal, to make a missile (One of our players is a Prodigy Engineer by Lore who nuked all his feats and stats into Lore Engineering and Craft) by basically combining 30 of the Witcher bombs, who we agreed work as unstable liquid inside of glass vials, and then using the crystal to make sure the liquid does not go inert... He at first agreed, but when I gathered all the necessary components, (Basically I hired a bunch of miners to get me Charcoal and Sulfur for Gunpowder, found a Chemist to make me Saltpeter to finalize it) and found the said Crystal, he kinda backed down and said I cant make it unless I explain by Pathfinder rules, how I make it, cause despite me knowing how it works IRL, it wont work in Pathfinder unless I explain it by rules.... Which is an issue for me.
Could someone maybe offer an advise or was the idea boomed to fail from the start ? Cause honestly both the Engineer and I are kinda dissapointed cause we spent a lot of time and gold into it... He even made a custom cannon capable of launching said missile...
Is the GM just asking for a reasonable analog from an existing rules source?
Bomb from Ultimate Combat (which is normally an acceptable rules source), though its sort of a siege weapon (though can be used without).
More personal sized: Pellet Grenade/Fuse Grenade
More high-tech: Aasen Mortar from an adventure path.
Or Rocket Launcher/Grenade from the Technology Guide.