In this video I will show you an easy way to upgrade your heavy weapons and to grind in general in your endgame.
Go to ++ Lab X ++ especially for heavy weapons level upgrade.
++ Nachtfalter ++ is also very good for none heavy weapons to easy upgrade. For heavy weapons it is a bit problematic since you do not get a lot of ammo during the mission.

Lab X is also the best way to get a lot of ++ experience points ++.

+++ Check out my video guide: +++

https://youtu.be/v1m-zuUAMqM

PS: Also good way to get the ++ sting like a bee achievement ++ - each run two + easy + Supersoldaten to sting.