Gonna haveto go with less.
At 1,000 I kept it within 3.5 MOA with my Barrett, I remember I opened up a good bit between 800 and 900 (MUCH harder)
Now, there's MANY people who are MUCH better shots than I.
But most hunters don't hunt with a 1MOA rifle.
So if we say 2MOA gun/ammo combo we're talking 16-18 inch grouping (Or area for one shot)
That's with NO varriation from the shooter, no matter the position.
We have tiny Deer.
I don't call that ethical.
It is not relevant that most hunters don't hunt with a 1 MOA rifle. Most hunters can't make an unsupported shot from 100 yards. We are not talking about most hunters. A number of people I know, myself included, hunt with a 1/2 MOA rifle. Besides, if you are going to do this, you would have specialized equipment so we are not talking about 16 - 18 inch grouping or a 2 MOA gun/ammo combination.
Your target size is going to be roughly 16" tall and 20 or so inches wide. For the sake of round numbers, we will call it 2 MOA tall. We know the exact distance to the target and we can assume the shooter knows the correct elevation to put on the rifle for that distance. The only elevation variation will be ammunition, but we have taken Xmeister's advanced reloading class so the ammo is capable of holding 1/2 MOA. The only other elevation question is how well can the shooter hold.
From position, I can shoot better than 2 MOA with a service rifle using post sights. With a aperture sights or a scope, it is more like 1/2 that, one of our forum members shot a group from the prone position at 600 yards with open sights that was less than 1/2 MOA tall. However, we don't have to worry about shooting with a sling. Since we are smart and prepared, we have a proper rest. Elevation holding errors are therefore minimized.
The big problem is the wind. With a proper rifle, you are still going to need to be able to call a full value wind within 2 mph for your first shot if you are unlucky enough to not have some kind of wind break (like shooting down a pipeline) or to not have the wind at somewhat less than a 60 - 90 degree angle. The wind drift on .223 ammunition used for highpower has about the same drift in inches at 600 yards as a 7mm or 300 RUM has at 880. I know there are 5 guys on BS.com who can put the first shot in a 12" ten ring at 600 yards with a service rifle nearly every time. They should be able to do the same in this situation.
The statement was that "there's maybe 5 or less people on this site who can shoot that distance accurately enough to hunt ethically." Putting ethics into the equation really muddies the water because ethics is in the eye of the beholder. Accuracy-wise, I believe there are more than 5 people on the forum who have the skills to make the shot given the proper equipment and situation (obviously a gusting full value wind would not be the proper situation). I personally limit myself to 400 yards and in although I have a new scope with an adjustable elevation turret that could spell trouble for something that lingers too long out to 600 yards. My rifle isn't set up for anything longer than that.
Tulse, I am not going to bet body parts on anyone else's skill. That doesn't mean that BS members like bjenkins can't make the shot.