It's nomenclature time!
template: a line of text with all the info jk needs to create the thing ingame.
projectile: the thing that jk creates from the template.
3do: three dimensional object - this is the file which contains all of the visual detail for your thing. just because this is the only part of a thing that you will "see" in the game doesn't mean a 3do is a thing (get it right jed addicts
)
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*gets off soap box.
I'm just saying this because "attaching a projectile tag" doesn't make any sense. It sounds like you're trying to change the template that your weapon cog is using - or at least part of the template. Your template will come from the *.jkl file of the level (which is inside a gob in the episode folder - extract using ConMan) or the static.jkl from res2.
JK's resource-loading priorities are confusing at first, but as long as you use the path switch and put all your resources in their appropriate subfolders (same as the folders conman shows, but in the path folder), everything will work fine.
Maybe that clears up a few things for you.
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Author of the
JK DataMaster,
Parsec,
Scribe, and the
EditPlus Cog Files.