Old 'traditional' wisdom said an 8" circle was about equal to the kill zone on a deer. I'd personally exclude the shoulder area and therefore drop that estimate to 6" on deer sized game for determining effective range. I myself get pissy if my arrows leave the 5 ring of an NFAA target at 40 yards with broadheads which is I think about 4". If you're hitting a grapefruit every shot at 40 yards then it's well within your effective hunting range, as long as you can do it with broadheads...