.38 S&W is an older semi-obsolete cartridges that has not had a revolver chambered for it in decades. It differs from the .38 Special in diameter, length, pressure, and power and the two cartridges are in no way, shape, or form interchangeable.
.38 S&W has a much lower pressure ceiling than .38 Special does. Maximum SAAMI pressure for .38 S&W is 14,500 psi as opposed to 17,000 psi and 20,000 psi for .38 Special and .38 Special +P respectively. The .38 S&W has a significantly shorter case than the .38 Special being only .775" long as opposed to 1.15" long for the .38 Special. The S&W also uses a slightly larger-diameter .360-.361 bullet as opposed to the .357-.358 bullet of the Special. This also means that the S&W's cartridge case is slightly wider at .3855" neck diameter as opposed to .379 for the Special.
A common misconception is that the .38 S&W cartridge can be fired in a .38 Special or .357 Magnum revolver. This is untrue as the S&W's larger case diameter would prevent it from chambering in a revolver made for one of the other two cartridges unless they had unusually oversize chambers. Also, firing an oversize .361 bullet through a .358 bore would cause an increase in pressure.
Standard factory ballistics for the .38 S&W are a 145-146grn bullet (usually a lead round nose) at 685fps for 150 ft. lbs. of energy. In a strong, solid-frame revolver like a S&W I, J, or K frame, handloaders can often get a bit better ballistics, but in an older top-break revolver one should not push the cartridge as top-breaks aren't the strongest action type in the first place.
Smith, and Wesson, and Me. -H. Callahan
Well waddaya know, one buwwet weft! -E. Fudd
All bad precedents begin as justifiable measures. -J. Caesar