First thing I would do to decide what bullet to use is measure the barrel's groove diameter. Slug it with a lead ball pushed from breech to muzzle, then carefully use a micrometer that gets repeatable readings to the ten-thousandths of an inch. Bullets smaller than groove diameter have never consistantly shot super accurate in any barrel.
Second, find a bullet of around 70 grains that's a few ten-thousandths bigger than your barrel's groove diameter. One even 7 or 8 ten-thousandths would still be very good.
Third, use an extruded powder of the same speed as H322 then work up loads that are safe. Use the powder and primer that produces the best accuracy.
Determine accuracy by the size of the largest group shot with a given load. Ignore the smallest ones. The largest one is what you can count on all the time; smallest ones are seldom repeated.