Well like all of them your going to have to experiment.
There will be no "magic load combo" to be found in mid October for the upcoming November Deer hunting season.
You could start now for next year,
The slow twists tend to like a tighter patch/ball combination and are more likely to give you two or more found balanced loads for accuracy.
One with a low charge and one with a higher charge.
You should try both .490 and .495 ball and both will need patch .015 or thicker like tom_in_vt said, your chances will be better in the .018-.020 range.
Starting at 70grns is a little high, I'd start at 60 and work each patch thickness variable in 5grn increments.
It's going to take some range time and shooting to get it right.
Don't forget to properly seat the powder charge and be sure to keep the nipple clean.
You should be able to dial it in sweet with only 150-200 rounds.
Need more?