Should the bullet be cast (20-1 or 16-1) at 0.001" or 0.002" or 0.003" larger than the nominal bore diameter? For instance, in a nominal 0.375" bore should one use a 0.0376" or a 0.377" or a 0.378" mold/bullet? 
Thanks.

Can also depend on the diameter of your freebore and even more so if breech seating. I used to believe .001 over "groove"at the baseband was ideal. But I now personally feel it should be at least .002 and I actually prefer my own to now being .003. I am also using 16-1 and from the nose to the baseband I have found anything from bore riding, cylindrical too tapered as not being as critical as the baseband fit. 
I don't feel using the bore diameter is a good reference point to try and use and even at point .003 over the bore diameter it can still be well under the groove diameter size.

Chuckster wrote on Sep 24^th, 2019 at 11:02am:

You are, of course, correct. My new Shilen barrel is 0.3670" bore x 0.375" groove.
Will be going with a 0.376" mold. Be interesting to see how a lapped Shilen barrel works.

Ditto Gunlaker,
SSShooter, you Need to wait until you know what the chamber/freebore, and FF case I.D. is so you can get the bullet fit to those dimensions. 
beltfed/arnie

I like .002 over too, exception when using black powder you can get away with less due to bump up. Agree with Froggy on 1/25 too.

Boats