.357 magnum, first loads!

[biker_bill]

Yes, concur. I looked it up and see that the starting load is indeed 21. It's been a while since I loaded 125 GR 357 mags. That being said, I also recommend you work it up to mid to upper range. As I recall, H110 is one of those powders that like to be loaded in the upper range.

Excellent advice.
H110 is DEFINITELY one of those powders that doesn't do well when loaded light.
You'll have un-burnt powder and you'll chrono all over the place.
Doesn't matter what you're loading and pretty much doesn't depend on the primer, though a hotter primer does help in the larger calibers....
As stated work to get to at least the mid-range.

 

[1006]

Red Dot is an excellent powder for light to medium power loads in the the 38 or 357 cases. I use it in everything(9mm,40,45,38/357) that it will fit into. It fills the case--bulky.

231/HP-38 is another good one for light loads. Although it does not fill the case as well as Red Dot, it is cleaner and just as accurate.

 

[Bayou]

I shoot a lot of 38 SPL in 357 mag framed wheel guns. So, I also like the stoutest 38 SPL loads. These tend to be the "+P" loads. They are listed on the Hagdgon website for the various powders and weight bullets:

http://www.hodgdonreloading.com

Since I have a lot of 700-X powder, I load with that.