Actually, there are apparently 3 different receivers now. The stainless, which are Special Weapons receivers, the Hesse which is stamped and has the HK drum style sights, but within the last month, Century has apparently begun making their own stamped receiver for their CETME and G3 clones. Unfortunately, I don't know if there really is any way to tell them apart, as I don't think there are any markings on the receiver indicating the original manufacturer. I've seen places advertising the new receiver, but I haven't actually heard any reports on them yet.
Rocko