Yes, you can shoot .38 S&W Special in a .357 Mag. The .357 Mag is nothing more than a .38 S&W Spl that has been lengthened by 1/10 inch. (or, for you .357 fans, a .38 Spl is a .357 Mag that has been trimmed back a 1/10"
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What you can't shoot is .38 S&W (regular). Head diameter is wrong. (It shouldn't fit in the cylinder anyway)
Dean
I should add, Welcome to the wonderful world of nonsensical naming of cartridges. .38 (in this case) really is .357 in diameter.