By the way I did find a very old thread here on the forum. Of people necking down the 7.62x39 case to PPC..
Got to give that a try!
The late Glen Zediker used 7.62X39mm brass as a s starting point for 22PPC in an AR-15 XTC rifle. He details the conversion process in his book The Competitive AR15. Frankly, the workload is way OTT if 220 Russian brass is available except maybe for high volume users in a discipline where you're likely to lose cases.