Reading the thread on 45 leading leads to thequestion: After measuring your cylinder throats which size do you use in relationship to that measurement?

As tight as will chamber.

In two instances, I use a .431 bullet in a ..430 throat, .429 groove guns with hard bullets. You dont want obturation as it may plate the cylinder face.
In others, the bullet can be up to .001 smaller than the throat if snug fitting isnt feasible so alloy needs to be bumpable with pressure. Whatever it takes to seal the base and support the bullet the maximum amount. The more unsupported deformation, the hollower the accuracy. The fatter the better.

For rifles I size to chamber with some resistance with the throat. Even better is some land contact is made. Fixed chambered autoloaders are done in the same fashion, obviously with reliability in the equation.

Anyone else?

I try to size the same as the throats. I don’t worry about bore diameter much unless it is larger than the throats. Example: if the throat measures .431, and the bore is .429, I size to .431.............lube is LBT Blue Soft. I must be doing something right as I get good accuracy without much if any leading. My cast bullets are 15 BHN which is probably a little harder than necessary for reduced loads (950-1000 FPS) but I use the same bullets for full power loads.

Thanks guys. I use a pin gauge to measure the throats. I use that size to begin. If I can't push that bullet through the cylinder using a dowel & hand pressure I drop down one size. Everyone has their own method but that's what works for me.

After I started powder coating I quit worrying about precise sizing.

It's a good place to start by making sure that all the chamber throats are the same size and reaming them to match if needed. Ruger 45 Colt chambers can vary .005 in the same cylinder.

Had a SBH 44 once. One throat was 'bout .001 large. My gunsmith took care of that.