Weapon do not have have an actual fuel/MU value only vehicles wreck.
That's not how it works. Because you can salvage the destroyed weapon.
There's several problems with how it was implemented.
1- You can not salvage abandoned units. This includes vehicles. Therefore you will never get resources out of MGs or Mortars.
2- Teamweapons such as AT guns do leave a wreck, therefore you can salvage them. They give small amount of fuel/muni.
ISG/Pack Howie gives mp.
3- You can't salvage certain bigger support weapons.
You can do so with Soviet Howitzer, but not with B4.
You can't with LeFH, but you can with Pak43 (both OKW and OH).
4- Values were normalised, but you will never get those values out of it. All wrecks start with 50% HP when a unit is killed.
5- While the LeFH is not able to be harvested, it's the one the exception at been at full health.
6- KT is considered a super heavy.