This is why I cast from 2 molds at a time. Fill one set it down. Fill 2nd mold, set it down. Pick up first mold and bust sprue, dump bullets.
Rinse, repeat.
The time it takes to fill the 2nd mold and set it down is all the time it takes for the first molds sprue to harden sufficiently to bust that sprue.
I've done it this way since I started casting bullets about 1962.