yo jay the sormender can trigger equipment thru walls ex if a enemy is camping is by his landmine or claymore shot them with the ender and he does or is badly damage.(like so he see's it)
A good technique with the jokr is to find something to crouch underneath of where the zombies can't get you and just lock onto something in the distance. When you fire the jokr it will just hit what your underneath and kill all the zombies around you. The konni group trailers in the orlov military base are good for this
If taking down streak is an option for xp (if not just *intended* for launcher) then ground war is the way to go. That or the turret cheese in the first story mission in MWZ.
One way I farmed Weapon XP super easily was by playing Plunder. Every cache, chest, even medicine cupboards looted give the same weapon XP as a base kill (100 XP) so you can get loads of Weapon XP without even needing to try killing stuff. You can also max out WXP by using Cash Exfil Helis and Balloons which give XP also. Hope this helps for the other cursed weapons
Ugh i got all weapons liquid gold (yes the One trick camo is like a better version of gold) the Launchers WERE A PAIN the RGL was easy that's obvious but i struggled to get the JOKR as much as you did