Ditto to Sir Charles's advice.
Plus; Regret, there is one basic rule for B/P loading:- NO AIRSPACE.
You fill whatever case you are loading with Black Powder so that when you seat your bullet, you compress the powder about 1/8th of an inch. Apply a reasonable crimp to hold the bullet in place and prevent it turning in the case mouth, load and fire.
I have done it this way for 30 years and it works for me, other shooters will also have their own methods and opinions, but personally, I always stick by the basic rule:- NO AIRSPACE.
Good Luck, AE