Ethics to me is more than one question. Ethical to animals? Sure. In my observation, all weapons are pushed to the limits by some hunters. Is an 800+ yard shot with a .50 off a solid bench less ethical to the animal than a 70+ yard bow shot? A 400+ yard .270 prone shot? I don't see the difference.

Then you have ethics for other hunters. If you do what my friend said he wanted to do, but never went through with, you would set up in a blind on a mountain with dial-in benchrest and wait. Dial in to an elk at 1200 yds or more and pull the trigger with a string. If it got to that extreme, it would be unethical to other hunters in MY opinion and regs might have to change to accomodate. But there's no line - it's a judgement call based on opinoin from most hunters. Some could say that compound bows are unethical compared to long bows. Gunpowder projectiles are unethical compared to compound bows. .338 mags with bipods and power scopes unethical compared to .243 open sights.

I personally don't ever want to hunt with a benched .50 bmg, but I do use a .300 wsm with 3 to 9 scope off a bipod. Maybe I'm unethical.