Extra ammo that doesnt take space

After getting respawned from my deathbox i realized that i have 120 ammo in my inventory but it showed 270 on my weapon. After dropping all my ammo from my inventory i could still reload and it would take away from that 150 non-existent ammo so it isnt just a visual bug

as you can see the 5 bullets i shot are reduced from an imaginary pool
this was after i got respawned from my deathbox so they could be related