don't know about the Lee measure. Over the years I have tried several different things, but for cap and ball revolver, I use an empty cartridge case or a flask with a spout that measures the amount I want. It has been so long since I actually paid attention to what amount I use, that I don't even recall. I just remember that this measure goes with that gun. I did figure it out once years ago. With a revolver, there are so many variables, from lubes to hold, breathing and follow through, etc, that the actual amount of powder kind of became secondary. With my Ruger old army, when I get a little practice, I can shoot a three inch five shot group at 25 yds. I can do slightly better with my muzzleloading percussion pistol. I once shot a 1.3 inch five shot group at 25 yds with a 36 cal muzzleloading pistol. That was my personal best and got alot of attention from the other competitors. I measured then as I do now. an empty cartridge case, or flask with a spout.
I've done a lot of BPCR shooting too, I know the way I measure powder throws about 60 grains for my 45-70 loads. What I actually use has been long forgotten. I've used the same method for years. I have a flask with a short spout that measures about .44, but has a hole that is only 3/8 or so. I put the empty primed case over the spout and tip it up to allow the powder to flow into the case. I shake it back and forth three or four times to settle the powder, close the valve and withdraw the flask spout from the case. It leaves exactly the right amount of powder for a grease wad and Ideal 457-125 lead bullet to be seated down to leaving the last grease groove exposed. That's my load and I'm sticking to it with the results I have had over the years.
I played around with loads and charges for years, before I realized that sticking to one consistent load for each gun and adjusting my shooting got better results. While certainly, I am not getting my picture in the magazines and books, I won a great many local matches against guys that did measure each bullet or ball, measured their powder on an analytical scale etc. For short range pistol shooting, the exact powder charge is not as critical as for 100 yd rifle shooting. Breath, hold and follow through are the primary pistol shooting factors IMHO.