So that Elder Signs achievement.

Is there some trick to getting this thing to register? Have tried countless time during the applicable days to get the second sigil to count for this achievement and it still won’t work. I look at it from every angle possible, doesn’t work. I unload the ammo of every gun on the map into it, doesn’t work. I zoom in and out with every gun on the map, doesn’t work. I sit there starting at it for 20 minutes, doesn’t work. What do i have to do to get this thing to register so i can move on from it?