I am not sure why you would want to cast lead alloy .224" bullets. Excellent jacketed .224 bullets are so inexpensive that I hardly consider the expense for either of my 222s. This site has 55 grain bullets as cheap as 13.5 cents apiece. They even have one of my favorites, Hornady 55 grain V-max, for 16.5 cents each.
Why NOT cast .224 bullets?
I cast Lyman #225462 for my .223 Rem 788. It's a 55 gr. (casts closer to 60 gr w/Lyman #2 alloy). It's a double cavity mold and I've been using it for +25 years.
Loaded to +/-1,800 fps it'll hold well enough to take tree rats w/head shots out to +100 yds.
FYI - You can cast a pile of bullets in a short time when they're that small!
Good Luck and don't be dissuaded from your quest!