Do you mean: "air cooled"?
I have found applications where hardening lead bullets is counter productive. For instance I had a Winchester 94 Legendary Lawman in 38-55 Win. It had the true old bore diameter of .379 and I could find no bullet mould that would drop a bullet bigger than .375. So, the accuracy was pretty poor until I let the bullets air cool (and stay soft), When I shot the soft bullets with just under max for cast bullet loads listed by Lyman for 38-55, they evidently orbitrated (swelled to fill the bore, not sure of the spelling), and filled the bore adequately to give pretty good accuracy.