Good report! I trust all will proceed equally well.

As for the fireforming, let me suggest that you anneal the Bertram 500/416 brass before blowing it out.

I have blown out at least 100 Hornady .470NE cases to .500 3-1/4" (straight wall). My method is to use 11.5 grains of Unique or Red Dot (Bullseye equivalent), fill the case with cream of wheat, plug with a wad of newspaper balled up, and use for "dry-fire" practice. I have never had a case not to expand perfectly. However, I do notice that Hornady brass always exhibits color from annealing, which must be their final process.

On the other hand, I have found some Jamison brass to be rather hard and in need of annealing when purchased. That may be your problem.

I hope this helps. I'm not trying to be a "know-it-all."

Curly