This is interesting to me. I have tried cast bullets in a .470NE, a .500NE, and two days ago in a .450NE. In all cases, the accuracy was dismal. I've tried wheel weights, cast as is and heat treated. Light loads, full power, and everything in between. Different cast styles and weights. In the .450 I used Lyman 405 grain cast and heat treated, lubed with Lyman lube, with 91 grains of H4350. The good news is that they didn't key hole but the "pattern" was 10" @ 50 yards. Using the same bullet in a .450 marlin, accuracy was excellent at around 2" or less @ 50 yards. I'm thinking that the deep Ballard rifling in the.450 Marlin was able to deeply engrave and stabilize the bullets whereas the very shallow rifling in the modern double rifles was relatively ineffective. I've all but given up using cast bullets in my double rifles at this point.