Before selecting a mold you need to know what the groove-to-groove diameter of your barrel is.
Then order a mold the same diameter or .001 or .002 wider than your groove-to-groove diameter.
I use a .323 bullet in my .32 caliber barrel which has a groove-to-groove diameter of .321.
Then you need to match the bullet's length to match the twist of the rifling in your barrel.
You have to determine the twist of the rifling and then calculate the maximum bullet you can use with the Greenhill's formula.
(You need to Login or Register to view media files and links) I have a 11.5:1 twist which allows me to use a maximum length bullet of 1.35". I use a 1.298" long 235 grain bullet in my .32 caliber rifle.
Then you must select a bullet nose.
Flat nose - best for hunting with.
Spitzer nose - best for wind effect out to 200 yards.
Rounded nose (Creedmore/Postell) - best for 300 + yards
And match the nose diameter to your barrel's throat.
No throat - Money nose or tapered diameter bullet
Maximum Bullet Nose Diameter - same as land-to land diameter of your barrel
Then order a custom bullet that matches your rifle.