have you looked into using COW, and Bullseye?
IIRC, you fill the case with BE, and then weight that powder amount
divide by 10, and use that amount, top up to the top with COW and shoot it, holding it staight up.
if you need to, plug the end with crisco so you can load it easier.
if it doesn't fully form out, increase by 1%, then 2% etc until you get fully formed shoulders. use that amount for further fireforming.
this is going on memory, I'd have to check my books, but IIRC Ken Howell used the 10% BE technique.
before you try this, do a bit of research, to ensure the amount of BE.... any other fast powder would also work.