I read your post and I want to ask you to look at what you have done again. The bore is the surface of the rifling, it is the hole that was cut or bored into the barrel. The groove is the cut wider than the bore to make a relief cut and thus create rifling. The bullet you want to cast should be the groove dia. plus .001 or so. The bullet fills the groove and is cut/etched by the rifling. The bore has no effect at this point for consideration. When you slug your barrel the largest diamiter is the groove. that is what you must fill. Any less and you can have gas slip by the bullet and it can melt lead from the bullet (gas cutting) you want to fill the groove with a little extra to form a swedge fit. I think you are on the right track. you may be calling the groove the bore. I hope this helps. JB

To answer your specific question, geobee, I think your .359" bullets will be just right with a .358" chamber throat and .357" groove diameter. A little oversize is usually good with lead bullets, as long as the case necks aren't expanded by oversize bullets to the point of making the loaded round difficult to chamber.

I personally know of one exception. There are I am sure more.The Bator 35 cal 260 gr.bullets that I loaded had a long front end that also measured .359" dia. and my .358" dia. throat said " You ain't coming in here" and meant it. Just something to be aware of. Roger