We just
know things...
mysteriously... heh
Seriously, if you want to see what a weapon does, just click on it, when a unit or commander is wielding it.
Most of the time it will list all the special effects it does.
Sometimes, if it has both a secondaryeffect, and a secondaryeffectalways, only one will show up.
Also, I personally use the Dom3 Database, which has a lot of information about the game, and saves time in having to look it up in game.