I use .357 cases, rather than .38 for my target/plinking loads, since I shoot a lot of them and it doesn't crude up my cylinders as bad. I tried coming up with some really light loads with Universal and it didn't work too well for me either, even using a 158gr bullet with a good crimp. And I tried both standard and magnum primers, and couldn't tell any difference. I got a lot of smoke and soot out the front, but the sides of the cases would be covered in soot as well if the charge gets too light. And accuracy was poor at best. The only possible way to ever hit the 10 ring was to not aim at it.
My favorite now for shooting lead with light loads is Trail Boss. I really like that stuff, it burns clean, and gives a nice soft recoil.