Wiktionary
throw true
vb. to inherit a characteristic
Usage examples of "throw true".
She showed me a bar of lead twisted up into a knot, and said she was a good shot with it generly, but she'd wrenched her arm a day or two ago, and didn't know whether she could throw true now.
I am sure, though I have never seen them to ask since I was but four, that both believed my mother would throw true, a perfect child, a House treasure, and the Dowayne would take me in open-armed.