Never heard of them? the 30-378 was a wildcat originally, but mainstream now, well kinda. Holds more powder then the RUM, but costs alot more, and with alot more powder comes recoil. It really doesnt show a significant gain over the RUM either. Ive heard of the warbird, its another big case, thats about as well known as a 300 jarett. The RUM is about the biggest of the mainstream cartridges, and anything on that is well past deminishing returns IMO