Currently, as far as I can tell, there is no checking of any magic number in MRCReaderWriter. The only thing which controls the byte ordering is the hack having to do with looking for excessively large (and now excessively small) voxels.for example, if your magic number indicates big endian, but the data are actually stored as little endian, your output will be messed up - but the reader works perfectly as it should do.