What Caliber For Accuracy At 500 yards?

[gumpokc]

unless i misunderstand, your looking for the following:

accuracy to 500+
abiliaty to hunt varmits
possible use for bear as well

.300winmag sounds right up your alley.
.308 could also do these things, all depends on what your comfortable with,though the .300winmag will have a slight edge over it in most areas of performance.