I load and reload constantly, have since 1965. I make such loads as you write of BUT I cannot do as good a job as a producer such as UNDERWOOD: 1. Fastest powder possible for the 2 - 3 inch .38/.357 S&Ws to reduce flash which is unburned powder. Also reduces the velocity loss from the short barrels. 2. I use much slower powder, like H110, for the carbines with their 16, 20, & 24 inch barrels. 3. Use regular .38/.357 loads for the 4, 5, and 6 inch barrel revolvers. 3. Still working on load(s) for the 8 3/8 inch model 27.
Reloaders such as UNDERWOOD have access to & use non-canister grade powders that I cannot get. Those powders will do a better job meeting the three different requirements I have for shortest & longest barrel revolvers plus the carbines.
There used to be commercial AMMO producers that would work with US but they are mostly gone now or have gotten too big for custom orders. One example is CORE-BON, Peter's father I think, maybe. Another small producer used to make heavy hard cast deep penetrating bullets for the .44 MAG and .45/70 for bear defense. I am sorry but I have forgotten the name of that company.
I do not take offense with that "...buy a Rock Chucker" crack BUT I have worn-out two of those and now have four of the best presses available not counting the three Dillons.
Best wishes...