for "cannot find saved game : unknown_weapon_type_...." error :
I think we simply need to add our weapon's name like this or id == "wpn_fort" in the gamedata\scripts\news_main.script just after other weapons.
Edit : working
Skullhunter,
do you have an error message into the console when you kill a npc with a new weapon?
"cannot find saved game : unknown_weapon_type_...."
I don't undestand how I can fix it.