Why did the 223 Remington and 308 Winchester twist rates change for Vanguard rifles?

Weatherby has changed the twist rate of the Vanguard rifles in the 223 Remington and 308 Winchester chamberings to give the rifle the ability to accurately shoot longer, heavier bullets which are growing in popularity in these chamberings. The 223 Remington was changed from a 1-12" twist rate to a 1-9" twist rate. The twist rate will be the new 1-9" rate from serial number VB084281. The 308 Winchester was changed from a 1-12" twist rate to a 1-10" twist rate. The twist rate will be the new 1-10" rate from serial number VB046406.