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You need to remember there is not an easy answer to your question.
Barrel dimensions differ between manufacturers and cartridges.
Older rifles often have a different throat than new manufactured firearms, even when they are chambered for the same cartridge.
Lyman has a new edition of their Cast Bullet Handbook ready for release. If you get a copy of this book you will see a chart with bullets cast from the same mold using different alloys and their respective diameters. The chart is quite helpful in estimating as cast diameters of bullets.
You also need to be aware the various mold manufacturers traditionally use different bullet diameters for bullets intended for use in the same cartridges.
Ideal and then Lyman traditionally used oversize bullet diameters, until recently when Lyman reduced some of the bullet diameters. Ideal and Lyman both made molds marked with a “U” which were undersize. The “U” number molds were available on special order.
In general terms the fit of the bullet in the throat of your rifle or handgun is far more important to accuracy the bullet diameter Vs bore or groove diameter. I typically shoot all of my cast bullets “as cast” and lube by hand or tumble lube the bullets. You will be well served by studying a copy of the Lyman Cast Bullet Handbook and as the latest edition is now “overdue” at the vendors it will certainly be available shortly.
 

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As a collector and caster I have many molds: Ideal, Lyman, H&G, B&M, LBT, Lee, NEI and several other lesser known brands.
I have rifles from across a broad time line.
You have not mentioned what rifle and cartridge you are loading for. In general terms you will find the current Lee molds casting bullets at or very close to their specified diameter.
Some other brands of molds are also very close. If you ask Veral Smith at LBT for a mold which casts .401” diameter using a 1 – 10 mix, your bullets will be exactly that.

Cast bullet fit and lubricants are not difficult to understand once you have the books for study. In the book section there is a link to Phil Sharps Complete Guide to Handloading on a PDF file. Sharpe’s book will give you a great deal of basic information on bullet fit and lubrication.
 
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