dc clamp meter design with 10mA resolution

[justarandomelectron]

hello gang,
I wanted to design a dc clamp for measuring current with a resolution of 10mA. I am just measuring stuff upto 5A with 10mA resolution. I have some 49e laying around and a iron core. Now I have 2 choices, either make a open loop design or a closed loop with compensation winding. I think that open loop design will be worse since the resolution will be worse    , and the core will be magnetize after measurement even though slightly. Though I searched online but I couldn't find a detailed design guide on closed loop design. Can anyone help me? Also will the 49e be sufficient for measuring flux near zero point in closed loop design?

Also I found out another method called self oscillating fluxgate sensor with a single coil using a simple op amp . Anyone has any ideas about it too?