I don't know for sure....

by Glen, Monday, April 15, 2013, 11:25 (4243 days ago) @ Harry O-1

....about that specific die, but the other M dies I have are all have the M die stem mounted in an over-sized die body, so as to accept a wide variety of cartridge cases. I would expect the 10mm die to be similar, and should work for .38-40 just fine.