A couple thoughts. If your POI vs your POA is that far off on an adjustable sight gun, then a taller or shorter front sight or rear sight leaf may be in order. There should not be that much of a difference in POI with 240 / 250 grain bullets between 10 and 25 yards, unless you are shooting critical bullseye matches, maybe.

As far as unburned powder goes, there is almost always some depending on the load, and it is not really an issue as long as the load is accurate. I know it bothers some folks, but unless it is really bad, (and few known "book" loads are) I just clean the gun when I am done shooting and don't worry about it. I am not really familiar with the powders you are using, but generally, faster powders burn cleaner when used with light for caliber bullets, especially when being pushed to .44 spl velocities.

If your throats are oversized at .432, then your best accuracy will probably come with lead bullets sized to that diameter. Jacketed, if an option, are usually less sensitive to throat size, and .429 / .430 may work well for you. Another option for you may be cast or swaged lead .429 bullets with a hollow base, similar to what some factories load for the .45c, another gun with varying throat sizes. They work. You also might find softer cast or swaged bullets might tend to "bump up" upon firing, and better seal you throats. Can you obtain .432 bullet molds and cast your own?

A couple favorite powders for me when loading the .44 spl at less than 900 fps have been Red Dot and Win 231, both producing good accuracy and a relaitively clean burn with both 200 and 240 grain bullets.

Larry