The bore should be slugged to find groove to groove diameter. The throats must be a little larger from .005" but even if larger no harm is done. I will talk about my .44 SBH. Groove is .430" and throats are .4324".
Some will say you MUST make boolits to a snug fit to the throats but this is not true in most cases. I have no problems shooting .430" boolits or bullets. I normally use .432" but it depends on the mold and who made it. You just never want to shoot smaller boolits then groove size.
What is more important is the alloy and nose shape of the boolit. You want a truncated cone or RNFP so the nose pulls the cylinder in line with the bore, something a Keith can not do. You need a little play in the cylinder and on the pin, nothing super tight works unless the gun is PERFECT, hard to find.
Alloy must be hard or tough enough to take the rifling without skidding past the base band. Hard lead is great with a PB but if you soften lead a little, you need a gas check to arrest skid. Skid past the base opens gas channels and leads barrels.
Hard, brittle lube is no good, some will break out of grooves but any left will toss a boolit out of balance. I never liked Alox in any form, it burns in the bore and leaves ash. I only use Felix lube, soft and sticky.
The faster the powder, the harder the lead needs to be to prevent initial high pressure slump and skid. Unique, 231 and Bullseye can need as hard as 28 to 30 BHN.
I use 22 to 25 BHN with 296 and that is water dropped WW metal or an alloy with a little more antimony and tin added but still water dropped. Try to make lead act like your jacketed instead of trying to make soft lead work, it will not. Only BP can use soft lead.
A recovered boolit should look exactly like the one you loaded except for land and groove marks.
Anyway, as long as you have a boolit that is groove size to as much as .003" over, they will work but when you destroy grease grooves before or after entering the rifling, you will have a problem. Same as slumping a boolit in the forcing cone that removes the grease and the grooves before entering the rifling. Maintain boolit integrity from the chamber to the target.
Don't worry about a few thousandths at the throats, worry about what the powder and pressure does to the boolit. Never, ever believe in the "bump up" thing.