How Shots are "used"

[Gerry1]

Hello:

I was firing my Jagdpanzer at a crew so I use T and then W as I only wanted to fire the BMG that is in slot 4. (I know about the slots).

Before I fired it the number of shots available was 3:-:4:5
After firing only the BMG the shots went to 2:-3:4

Before I fired I thought I had 3 shots with the 75mm, 4 with the Nahverteidigungswaffe, and then 5 with the BMG. But when I fired the BMG it subtracted 1 from each slot. So I am guessing I misunderstood the shot count system?

Thanks.