recapping:
1. It's a bad idea. Cylinders are not (usually) drop in parts for many reasons.
2. .38 Special is not some "weak sister" cartridge. I have a reloading manual from WAAAY back with the warnings "Do not use maximum loads in anything other than new strong revolvers." These are now called "+P" loads. .38 Special is arguably comparable to 9mm. Hot-rodders get in arguments about how hot they can load 9mm so we just say "Yeah but .357 Magnum" and they admit defeat by a country mile. Nothing wrong with .38 Special or 9mm unless primary purpose is hunting deer.
3. The OP wants to know the best powder for reloading. Two things:
a. BULLSEYE. Fast powder.
Bullseye is an "ancient" fast powder. There are ample recipes for Bullseye. It smells like gunpowder should. Maybe it's a little bit dirty but I never really noticed. It's got a grand history and anything W231 can do, Bullseye can do.
Bullseye's middle aged competitor is W231. Maybe it's a little better but you really can't tell much of a difference. HP38 is a special can with graphics and marketing specifically for most handgun reloading. You take W231 and put it in a HP38 can and now it IS HP38.
b. Unique. Medium speed powder.
With heavier bullets a slower powder is better. Like Bullseye, Unique is one of the grandpa cowboy powders. It can do it all but is a bit chunky for metering, especially for very small loads, which is where Bullseye is best anyhow. Unique is really good.
2400 works but is only "better" than Unique as we get up to .357 magnum loadings and if you already load for .357 magnum this is good. Likewise for the shotgun powders like Blue Dot- they work too but if you reload shotgun shells they are even better.
To me, .38 Special is like oatmeal. I guess all the cool kids are eating Greek Yogurt and Kashi now. Take some real oatmeal and cook it up with milk, add some brown sugar, chopped walnuts and some blueberries- mmmm. Granted, you need to learn to turn on the stove and it might take a few minutes longer, but oatmeal is classic. And tasty.