300 ish yards to maybe 400. Even though my rifle shoots a nice 3-shot group of .64 inches, that was at an indoor range on those little tables with the butt against my shoulder. I am blessed if my whole system, including me, is 1 MOA in the field. When I am hunting, I use a tripod with a clamp. Even if seated in my little camp chair and the tripod legs played out.
If it looks like I might take a shot, I loosen the clamp to allow free recoil.
I drank the koolaid on 7 PRC and that is my new go to. Even with some people measuring 2800 fps, which is 200 below the box value of 3,000, it is still over 2,000 fps at 600 yards. 600 yards I might could do in a few years after some more work on my skills.
Some might think that is overkill. I have .308s and any one of them is good for 300 yards. I use to go by impact energy. Now, I go by impact velocity because what we need to know is the required velocity for the slug to petal out into a fat tissue disruptor.
I may change to copper, not because it might be a little faster, but because of the impact performance and better chance of an exit wound to trail the game. Especially if I am going for mule deer or barbary sheep like the Aoudad, which we have here in my state. My boss got one with his .300 WM. Then again, that is one of favorite hunting rounds.
TLDR: at my current skill level and comfort level, 300 yards. On the public land I have been hunting, the longest target zone I have ranged is 250 yards and I can be very steady for that.
I say the ethical shot is what the hunter and rifle are capable of. But also, within the limits of bullet performance.
A long time ago, in a galaxy far, far away....
Aaron at Gunwerks took his son and some friends and one of the Gunwerks 7 RM on an elk hunt. They posted on one hill and this big bull showed up on another hill. 1,376 yards. The kid, used to practicing at their 1,000 yard range. Made 2 shots. The second one brought theh bull down. I don't know if he actually missed on the first one. It can take more than one shot to bring down an elk, even at closer ranges.
Aaron was on a podcast a few months ago and regretted having that shot made. The bullet did not work well enough. It was simply too far. I think a lot of people at the time were thinking he was just doing it to show off his rifle.
And, again, it can take more than one shot. The Aoudad my boss shot with a .300 WM 200 gr? He shot him right through the boiler room at 220 yards. That ram turned and was charging straight at him while he racked another round. As soon as it was into battery, the ram dropped, having run about 30 to 40 yards on his last heartbeat.
Here he is, on the left.