I think the OP is using a RCBS press.
Lee and Redding do a .357 die set and a .38 special die set. The .357 dies can't load .38 spec cases.
http://leeprecision.com/3-die-set-357-mag-carbide.html
Normal routine would be to use .38 spec dies (sometimes marked .38/357) and if you don't like resetting your dies you can fit a spacer under the locking ring.
http://www.midwayusa.com/product/312...ial-357-magnum