You might try using cardboard "gas checks", actually just a cardboard disc under the bullet. They whole idea is to isolate the bullet from the hot gases produced as the powder burns and this works great. I have used it in 45/120, 416 rigby and 50/140 with excellent results, no leading and very good accuracy. Cut to slightly over bullet diameter they just go in with the bullet and many of our loads are slightly compressed, so placement or movement after loading is not a problem.