The real answer to your question is: however far you can accurately hit your target I the optimum kill zone. Of course, this will change for each person with variable weather conditions. If someone online says the ethical distance is XXXyds, it's not a license to lob bullets out at that distance if YOU are not familiar and competent at that distance.
I've guided loads of hunters over the past 3 decades that claimed to be "good" to XXXyds and were, actually, only good to 1/2 that distance on their best day. Lately, the LR craze and availability of off the shelf rifles capable of LR shots has only magnified this issue. For the past 8 years I've been involved in blood tracking wounded deer here in S. Texas and we're seeing more and more guys with these fancy rifles, capable of 800+ yard shots, gut shooting (or worse) deer at 200. It's ridiculous.
There are guys that can "ethically" shoot elk at 1500yds but they practice regularly at that range and further. "Ethical" implies near certain confidence in the shot. If you have to wonder about making the shot, DONT pull the trigger.
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