qz...
What did your avatar buck score?
ONLY way I do it is to compare everything I can to mine. On 10 pointers....I just score it as an 8 and add in either the G2's or the G4's (whichever it more resembles my buck as to omit).
I've learned that most MB's are between 17 and 22 inches....can get pretty close on the H's and the spread's a guess that can't be but so far off.
It's fun for me to guess....and most times nobody can prove you wrong, anyways