I lucked out a couple years ago and found a new .450
Nitro express Hornady die set on eBay or Gunbroker for about $65.00 delivered. They work fine for my .450 3 1/4" BPE double rifle, but some people seem to have a problem using the newer dies to load for old .450 BPE's due to some older guns having slightly smaller chamber dimensions.
Some guys get around this by having their chambers reamed to modern dimensions, while others choose to order slightly undersize sizing dies from RCBS or CH4D. Another possible solution is to run the brass a tad further into the die by using a shell holder that has been ground thinner, and driving the well lubed cases out with a wooden dowel.
If you have fired your rifle, you may want to measure your fired brass before getting in too deep. Or do a Cerrosafe chamber cast so you don't get stuck with dies you can't use.
