Complex sentence: In August 1901, the case hardened receiver wa 100,000 second model rifles were produced with case hardened receivers, and 200,000 were produced with blued receivers.
Split into simpler sentences: In August 1901, the case hardened receiver was changed to a blued version. Approximately 100,000 second model rifles were produced with case hardened receivers, and 200,000 were produced with blued receivers.