I've always used my Mark I eyebone to boresight, centering some object out around a hundred yards in the bore and tweaking the scope to match.
What I've found through the years is that any conventional bolt action with a low set of rings/bases, dead on at 25 yards is generally about two to three inches high at 100 yards and within a couple of inches sideways.
I've always zeroed all my deer rifles for two inches high at 100, which is right at dead on at 200. Maybe 225 for magnums. Six inches low at 300, and maybeso around five inches for the hotshots.