An objective data-based view of acceptable accuracy...
I am on record for saying that it is a rare modern (i.e. CNC machined) hunting rifle that does not hold 1 MOA with decent ammunition. All my Blaser R8 barrels do, and that is good enough for me because the stark reality is that virtually nobody, me and AH crowd respectfully included, shoots
reliably and predictably less than an MOA from a field hunting position*.
* would-be game sniper generally included...
I can also vividly remember reading in the 1980's and 1990's all sorts of great gun writers (e.g. Finn Aagaard, Ross Seyfried, Ken Waters, Layne Simpson, Craig Boddington, Bob Milek, Ken Elliott, Gary Sitton, and all the gang at Petersen's Publishing) for whom the Holy Grail was a 1 MOA hunting rifle, and who were perfectly willing to accept 1.5 or even 2 MOA from a factory Win 70 or Rem 700.
Older rifles, and even older military rifles, can shoot just as well, or better, or can shoot ... all over the place. What with worn out barrels (e.g. too many solids, or too much vigorous barrel 'cleaning' with steel rods), corroded bores (e.g. mercury primers and cordite); poorly rifled barrels or poorly reamed chambers from commercial high-volume, or military war-time production on worn out machinery and/or blunt cutting tools, etc. etc. etc.
But what is the definition of "acceptable accuracy"?
Acceptable accuracy means hitting the target where intended, and in hunting terms, killing the game cleanly (i.e. ethically).
The question is: what accuracy is required to hit the vital area of the game?
This is related to the size of the game.
Tiny Ten: ~4 to 6" vital area.
A 6" circle represents 2 MOA at 300 yards...
A 2" group at 100 yard is technically acceptable.
Pronghorn / small deer / small African antelopes: ~8" to 9" vital area.
A 9" circle represents 3 MOA at 300 yards...
A 3" group at 100 yard is technically acceptable.
Medium size deer / medium African antelope: ~10" to 11"vital area.
A 11" circle represents 3.6 MOA at 300 yards...
A 3.6" group at 100 yard is technically acceptable !?
Large deer / North American wild sheep / mountain goat: ~11" to 14" vital area.
A 14" circle represents 4.6 MOA at 300 yards...
A 4.6" group at 100 yard is technically acceptable !?!?
Elk / large African antelope: ~14" to 16" vital area.
A 16" circle represents 5.3 MOA at 300 yards...
A 5.3" group at 100 yard is technically acceptable !?!?!?
Moose / Eland: ~18" to 21" vital area.
A 21" circle represents 7 MOA at 300 yards...
A 7" group at 100 yard is technically acceptable !?!?!?!?!?!?!?!?!?!?!?
Of course all the above numbers need recalculation if the maximum shooting distance exceeds 300 yards, but few folks among the millions of licensed hunters have any business attempting to shoot past 300 yards from a field position anyway*.
* I would add that the AH crowd should generally not consider itself as the shooting baseline. I have verified many times that our shooting skills are vastly superior to that of the average hunting Joe who shoots 3 to 5 rounds per year.
Do not rush to lick the stamp on the hate mail, I am not advocating that 7 MOA is "acceptable accuracy", but the fact is that I have shot as a kid many captured 8mm K98 or .303 SMLE parachuted to the French Alps resistance in WWII, that shot 5 rounds in 6" at 100 meters (6 MOA) with stowed away WWII military ammo and were considered by their owner perfectly acceptable for Chamois hunting (as in: 'got the job done') out to 150 to 200 meters, and sometimes farther, with their original military iron sights. A case in point where 6 MOA was considered perfectly acceptable accuracy...
But this was then, and now is now, and I would venture to say that "culturally" the modern objective meaning of desirable accuracy is probably 1 MOA or less, and acceptable accuracy is probably 2 MOA or less.
Never mind that many (most?) hunters have difficulty holding 2 or even 3 MOA from the bench, and 6 MOA from a hunting position*
* see above note.
If you doubt me, grab a sample of any 10 hunters in any hunting camp, be it in America, Europe or Africa, put a 6" steel plate at 100 yards, and invite them to shoot. I will wager that results will be better in Africa due to folks using sticks (which remain less used in America and Europe), but results are still bound to be fascinating*
* see above note.
And when it comes to used rifles, "acceptable accuracy" is in the eyes of the beholder, or should I say the seller, so it mean exactly ... nothing, zero, zilch, pure snake oil.
But then again, it is not all that different from buying a new rifle: you have no idea how it will shoot until you shoot it. Not to mention that your preferred load / bullet may or may not fly well from that pipe.
In summary, while you can rarely get a proof target with a used rifle (and not necessarily trust it if you get it), it is easy to get decent quality pictures of the bore to verify that it is still in decent shape with crip lands and grooves. If that is the case, you stand a very good chance that a post WW II rifle will hold 2 MOA, or maybe 3 MOA at worse, which is still technically acceptable for about any hunting out to 300 yards, aside from the Tiny Ten.