I think cases can be made with cut down 32 ga shot shells an forming by backing of the 56-46 dies.I will give it a go tomorrow an let you know how it works,the bullet is the biggest problem,I think it will be a custom mould a custom mould or nothing .If you must reline the barrel(something that I would have trouble doing ) I would go for a 1 in 24 twist .458 ,56-46 Spencer lined barrel,this is by fare the most accurate Spencer calibre that I have used and components for reloading are readily available.OK the forming of the case worked out to be very easy ,cut 32 ga shot sell to 1.4 ,annealed anran into 56-46 CH4 die till the shoulder was .958 forward(I would keep trying for fit but I belive this will be very close)trim to 1.2 OAL and expand with expanding plug until out side of cass mouth around .491.Now the bullet,with a 1in 52 twist a short .55 long bullet of .483 + or - to fit throat with a 0.2 long heel and a grease groove .2 ahead of heel,because the cartridge is a bottle neck one the nose would be best be only slightly rounded,OAL will be 1.6 inches