Good honest report. Yes a 200 meter zero will end up similar too Mickys rule of 3 and will help. You just have to aim dead centre at reasonable ranges. Other ideas- if you cant afford the rangefinder, then when you are just out and walking around, pick an object in the distance and guess what it is, then pace it out. Keep doing that and your estimation will improve.
If you have access to a place that doesn't mind you firing shots, go rock hunting. Shoot rocks at different ranges from different spots and angles. It all improves your range estimation.
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