Bramble,

1. Start with the load that works best with the standard bullet weight. For your rifle, that is a 480 grain Woodleigh.

2. Take a lighter bullet of the same shape (RN, FP, whatever) and shoot the same load, very carefully.

3. If all works out, it should shoot low. Don't worry too much it they don't cross.

4. Back off 1 grain at a time until you are shooting a reasonable group.

5. Above all, you must keep meticulous records and shoot very very precisely.

This has worked for me every time.