I had a set of the Zings in BeCu. They are one of those sets I still kick myself for letting go. Was funny that Ping did the complete set of Zings in BeCu but did not in the Zing 2's. Ping only made Zing 2 wedges in BeCu. The absence of BeCu irons in the Ping line was short. The iSi's quickly followed the Zing 2's and were in SST, BeCu, and BeNi.
Son-in-law has a set of the iSi BeCu irons, 1 through LW. Something like 12 clubs. All same serial number. All from Ping WRX with the S400 DG shafts.
20 years ago, while dating our daughter, he wanted me to find him some BeCu irons. I found that set priced right and picked them up for him. I let him know I had them. He brought cash to pay me for them the next weekend when he came to pick up our daughter. He told her he had a surprise for her. She, of course, thought it was a diamond. When he showed her the new irons, I don't believe in her 45 years I've ever seen her that mad. Once she quit screaming, he reached in his pocket and pulled out the diamond engagement ring. For a moment, we didn't think she was going to accept it. He still has those irons, but hasn't played them for years.