I don't have personal experience shooting that far, but a regular on another hunting website regularly takes deer with his Omega in the 200 - 300 yard range. He uses the 200 grain Shockwave, a BDC or Mil-dot scope, has a rangefinder, and practices a heckuva lot. He's also stated that he'd never even think about a long shot with the ML if there is any wind - wind affects ML bullets MUCH more than centerfire rifle bullets.
So sure, it's possible and in my book, ethical IF - you have the right setup (rifle/load combo) that will get you there, a BDC or Mil-Dot scope, a rangefinder, and you practice a lot at those ranges. 300 yards probably is really close to the limit though - even with a compensating scope and rangefinder, you just lose too much velocity, energy and trajectory to make 1 shot kills much past that.