I don't know what Smack is using, but I'm using straight Lapua 6.5 Grendel brass in my 243 LBC barrel with no neck turning. I've also tried forming from 7.62x39 brass and didn't need to neck turn for that either, at least in regards to chamber neck dimensions.
That's with BHW's 243 LBC chamber; with other variations of this cartridge you may or may not need to neck turn. If you were to chamber one of these yourself with a 6 PPC reamer, you'd end up with something that required neck turning and thin necks in most cases.
