My Dad had two of these at one time, and as I was continuing the process of going through his accumulation of stuff, I found a set of RCBS dies for .280 Ross and a bag of some kind of huge, unbelted 6.5 European cartridge he used to form brass from.
I was kind of interested in the rifles back in the day, it was quite a ground breaking ballistic development. Sadly, it seems Dad must have sold them off at some point, these dies should have gone with one of them.
There's one on gunbroker right now; https://www.gunbroker.com/item/874178340
I really doubt I'll ever own one, but wouldn't rule it out completely, I like oddball stuff. Anybody have experience with these? I know it used an oversized 7mm bullet, which was OK with Dad as he shot cast in them. I'd kind of like to hear anybody's thoughts on them.