Hey Robctwo,
I know you were speaking about reloading both 38 and 357, but I did not notice anything about whether you were also talking about loading for 38 and 357 revolvers. If you are loading both calibers for both 38 and 357 guns, then just ignore what follows.
On the other hand, if you only have a 357 pistol, the whole idea of loading 38 cases to use in your 357 just because you happen to have a supply of 38 cases seems like a waste of time to me. I freely admit this is just my opinion, and others may disagree with me.
I know you mentioned you have 300 .357 cases and 200 .38 cases, and I know .38 cartridges can be used in .357 pistols, but unless you are planning on shooting .38 cartridges in a .38 pistol, it seems more bother to reload them to use in a .357. My reason for feeling this way is because you have to change die settings between the two, and there are those who are inclined to change powders between the two.
My thoughts are if you want to shoot .38 rounds in a .357 pistol, why not just load your ".38" round in a .357 case? Of course you may want to use different bullets which may also require changing the seating die, but it still seems easier if you simply stick with .357 cases.
Now, after all that opinionizing, you will probably tell me you have both a .38 and a .357 pistol, and I just wasted time and space.
Best wishes,
Dave Wile