Messing with the powder charge will disappoint you, I expect. I tried that with a fairly hefty Dan Wesson with a 6" barrel in .357 magnum years ago. The amount of vertical shift in point of impact (POI) with powder charge proved to be small compared to changing bullet weight.
What affects the vertical POI in a revolver is how much the recoil moment pivoting around your grip elevates the muzzle before the bullet clears it. There are two things that can increase that elevation: increasing recoil force and increasing barrel time. But what happens when you change the powder charge weight is those two factors change in opposite directions, tending to cancel each other out. That is, lower the charge and you reduce the recoil force, but lengthen the barrel time. Raise the charge and you increase the recoil force but shorten the barrel time.
The two effects don't cancel exactly. This is because the average force on the base of the bullet accelerates it, and acceleration is a function of the square of time. So halving the average force pushing the bullet base only increases the barrel time by a factor of the square root of 2 (1.4142…) and not by an exactly compensating factor of 2. Nonetheless, when I did the experiment back the 1980s, if memory serves, changing between 125 and 158-grain bullets shifted POI in my revolver about 3-4" (maybe at 50 feet; I don't recall the test range any longer), while running a wide range of powder charges under either bullet only made about 1" of difference. I may not be remembering the numbers exactly, but the difference in the relative effect on POI is along the lines of those sorts of ratios.
If you shoot the 300's and find the compensation incorrect, you can at least find out what the POI difference for that weight made, and then order cast bullets or even a custom mold for exactly the weight you need. A simple linear interpolation or extrapolation should be pretty close. If you need help with that, PM me.
If you take a cleaning patch or a bit of rag and rub molybdenum disulfide powder on the bullet and put a little pinch on top of the powder in the case, you will find you reduce the engraving force of those jacketed bullets to nearly the level of a cast bullet. It's a good way to get an estimate of what you need. You might find you need a 285-grain bullet or a 325-grain bullet or some other value to get your sights timed exactly.