You are on the right path here but simply have not taken it far enough. Cast bullet revolver accuracy is more dependent on throat-bullet fit than any other factor, assuming other good loading practices. The reason is that undersized lead bullets are subject to gas cutting, which will positively ruin their accuracy potential. Most of the gas cutting takes place while the bullet is in the throat. To give just one example of how good fit of bullet to throats pays off, my Redhawk went from a best of 2" at 25 yards to a constant (Ransom Rest) average of 3/4" with a simple bullet diameter change. Throats in this gun are .4345" and I use .434" cast/swaged lead bullets in it.
Try this
Take a SOFT lead bullet and squeeze it gently in a vice until it is about .010" oversize (say about .436-.440" for a .44 cal. car- tridge). Attempt to push this slug through each throat of your cylinder using hand pressure only. If it will not pass through, your slug is large enough. If it will pass you must increase the diameter slightly.
Before doing the following, remove the cylinder from the gun, clean it of ALL lead or copper fouling, lube it lightly and make sure that it is solidly supported on an appropriate wooden block.
With an appropriately sized brass drift, carefully drive the slug through each throat from the end of the chamber where the cartridge is normally inserted. What you are attempting here is to find the diameter of the smallest throat, so handle the soft lead carefully and drive it straight to avoid distorting the slug. This may take a couple of practice runs because the transition between the area of the chamber where the brass case resides and the area into which the bullet projects (throat) varies from cylinder to cylinder. Some cylinders have a sharp step while others have a relatively long smooth transition. If the gun that you are working with has a sharp step it may be easier to minimize the distortion by driving it from the other end of the cylinder.
After you have completed the above, you have the "ideal" bullet diameter to be fired in your gun and you will be very fortunate if the bullet is the nominal diameter for that caliber. Usually you will find that it is somewhat larger. For the time being don't worry about the difference in the throats in a particular cylinder. I find that even though they are sometimes badly oversize, they usually do not vary much more than about .0005".
An exception that would negate this approach would be if you encountered a barrel that slugs larger than your throats. The only solution to this unfortunate situation is to either open the throats to .001" or .002" larger than the bore or to get a new gun. Fortunately, this occurrence is rare (I haven't yet run into the problem, but have read of others who have).
Another exception is the condition where the oversize bullet is so large that when it is loaded into the brass, the cartridge cannot be chambered. In cases where this condition is just marginal, a taper crimp will solve the problem. Where it is more extreme, the chamber (but NOT throat) will need to be enlarged to accommodate the cartridge, although if the gun is new, return it to the manufacturer.
Remember that when shooting cast bullets, the size of the expander plug is very important, and if one uses a plug of the standard sizes normally supplied by the manufacturer, the oversize bullet will be sized down when it is seated in the brass case thus ruining all of the above effort. Your expander plug for cast bullets should be .001 to .002 smaller than your new bullet diameter.
The way that I accomplish this is to keep a supply of next- caliber-up Lyman expander plugs, then when I need a particular size, I con a machinist friend to turn one to the proper diameter. The Lyman is a very good design because it has the step that makes for an easy way to start the bullet into the case with the bullet axis concentric with the case axis, a VERY important condition in pistol and rifle ammunition.
Still another problem, although not a cylinder problem, is one that few shooters know exists and is directly related. In most revolvers, the area of the bore directly adjacent to the forcing cone where the barrel is screwed into the frame is sometimes smaller than the rest of the bore. This damages the bullet much the same as an undersized throat and, unfortunately, is a very common occurrence.
The solution is to lap the bore with a cast bore lap to remove the constriction. That is not the easiest job for the inexperienced. An alternative is to shoot several hundred rounds (200-500) depending on the amount of constriction, charged with a proper lapping compound. This has the added advantages of polishing the rest of the bore and providing a very slight taper to the bore for excellent cast bullet shooting and will do a great job of minimizing leading. It is important that a PROPER lapping compound be used. Again, Veral Smith of Cast Bullets Technology has the proper stuff for about $10.
You will find, that with properly fit bullets, alloy hardness will not be nearly as critical from low velocity target loads to the highest velocities that your Super Redhawk will handle.
Custom molds to fit your gun are available from LBT for little more than commercial ones.