SOLVED! I was already casting to AWM in that function, so I made a new variable in the AWM bp called RealTotalAmmo, which is being set by that same cast to AWM function in the HUD bp. So now, when I equip the AWM, the RealTotalAmmo is live at runtime, and I can use that number to interact with other runtime elements in the level.
Expensive? Probably yeah. But it works! XD