Why complicate things with two different case lengths requiring die adjustments unless you have a 44 special gun to load for too? Unless you just happen to have a pile of 44 special brass, which I doubt. Besides, when loading for my 66 or 686 I use only magnum brass because I have enough of it, even for light loads. Although I get that 38 brass is a lot more plentiful, in which case shoot what you got. Plus, after a long session of shooting lead from special cases you can get a ring built up that will make the magnum rounds tight. Shoot what you got but don't create issues you don't already have.