I use extra wads or corn meal for fillers, to take up space in the chamber with lighter loads.
Cream of Wheat is often suggested, but it's almost imcompressible. Corn meal is fairly compressible, so if you add a little more than needed, it's not a problem.
Add too much Cream of Wheat and you have to scoop it out with a Popsicle stick or the scraping spoon on a pipe tool (handy tools in the shooting box, by the way).
The use of fillers has been debated for years. Frankly, I feel it's overemphasized, especially on the Colt design with its primitive sights.
I've not been able to find a difference -- on real targets, from a benchrest, at a measured 25 yards -- between using a filler with lighter loads and not using one.
But, I tend to use fillers on my Remington .36s and .44s because the Remington rammer is so much shorter than the Colt's, and with reduced loads it won't push the ball down firmly on the powder.
In my box I also have some short plugs of hardwood dowel -- 5/16 for the .36 and 7/16 for the .44s -- for use with light target loads.
I ram the ball down with the revolver's rammer as far as it will go, then pull the rammer up and insert the plug in the chamber. The rammer comes down again and the plug transfers its energy against the ball, ensuring the ball is down firmly on the powder.
Then I remove the plug. Removing the plug is very important, as it may create an obstruction if left in front of the ball and raise pressures catastrophically.
Using this system, I've not found any difference between a deeply seated ball and one brought near the chamber mouth by the use of fillers.
But, using the wooden plugs is a clumsy system.
It's far easier just to use extra wads, or corn meal on top of a single wad, to ensure there are no gaps between the components.
Using filler to supposedly promote greater accuracy is, I believe, a moot point when you consider the primitive sights on the Colt design. Even the fixed-sight Remingtons are far from ideal for super-fine target work. Modern, adjustable Patridge sights on a Remington might be able to indicate a difference between a deep-seated ball and one with filler that puts the ball nearer the chamber mouth.
Even then, it may not be noticeable.
I'd like to put a pistol scope on a Remington and Colt someday, and see if it makes a noticeable difference. I think it might, but perhaps of 1/4" or less in total group size.
There's far more variance than that in my 57-year-old eyeballs trying to align original-design Remington or Colt sights.