I have been handloading the 38 Special for over 50 years and it is without a doubt my favorite sixgun cartridge. I don't use bullets harder than ACWW and often softer. I prefer to use an expander the same size or .001 under bullet diameter to keep deforming the bullets. With some brass springback and a proper crimp, this works just fine for me.
Over the years I have accumulated a fair amount of loading gear for the 38 Special and thought I would show you a little about how it has evolved and some special needs.
First pic is of some RCBS expanders and from left to right they are;
1. A 1958 expander that measures .357. This is before jacketed bullets became popular.
2. A 1980 expander that measures .356. This is after jacketed bullets became popular.
3. An older .357 expander I modified for wadcutter use. The bullets seat deeper in the case and therefor the case needs to be expanded deeper as well. The second step for bullet seating is .360.
4. A special .3585 long expander for hollow base wadcutters. These long bullets with thin skirts can be easily deform with a regular expander. Use this only in wadcutter brass as they will bulge regular 38 Special brass to the point they will not chamber. Sorry to say, but RCBS no longer offers these special expanders.
Second pic is of some Lyman expanders and left to right they are;
1. A 310 expander that measures .357 (so marked) with a seating step of .359.
2. A 310 expander that mesures .358 (so marked) with a seating step of .361.
3. Current "M" style expander that measures .356 with a seating step of .360.
I find it interesting that Lyman can't seem to make up their mind what an expander should look like.