I hunted a farm many years ago. The farmer's son used a Remington 700 in .243 caliber. I saw where his stand was, and later that week the farmer told me where the kid shot the deer he'd taken, at. It had to be close to 300 yards. And he said that .243 planted that buck right there. I "think" he shot factory ammo.
Congratulations to your son. Its nice when a rifle does what they should.