You should not need a die set
Bertrand do the brass
Providing you use the brass for the same rifle (which you will) the cases should not need resizing
Decap with a fine punch or grind down a hard nail
Recap (CAREFULLY!) with a hammer GENTLY
If using BP have milk carton wads with lube cookie in between (beeswax/crisco) on top of powder
If using Nitro for black use filler, small volumes of powder in large cases can be dangerous
Bell case mouths very slightly with taper punch check it will still chamber
use a vice to carefully fit bullet (ensure the bullet does not cant sideways
check overall length
There is a very good sticky on British Militaria Forums on loading the No.2 Musket
It is what the .577/450 should have been, very good to reload
If I can find time (too much work!!) I will repost pics of my WR Cape rifle with good pics of the sights in .577/450 and 12 G
If you trace my posts you can find it but I cannot work out how to make a connection

Good luck

TH44