Hey, I'm glad you like it ^^
So, you can't upload schematics to your server? Do you know the server owner and could ask them if they can put the schematic into the server's schematics folder?

I don't make videos, so the only way I could show you how to build it would be taking screenshots of each layer, maybe.

Or you paste the schematic in singleplayer. Then you can take a close look at the cannon and examine how it's built.

You were talking about "schematica", is that supposed to be the plural of "schematic" or are you talking about the schematica mod?
To my knowledge the schematica mod only worked up until version 1.12, since 1.13 it's broken.
So if you're going to paste the schematic somewhere, I would recommend using World Edit. Most build servers support World Edit or FAWE, anyway. Just as a side note.

It definitely won't work in 1.12 because I built this gun in 1.14 and it uses blocks that weren't introduced yet in 1.12. But theorethically it should work in 1.15.
Did you use World Edit for Bukkit when trying to paste this schematic?

Can only agree there even tho this isn't a railgun, it's a totally normal gunpowder powered cannon xD

Yes