Thread: How to tell the caliber of projectiles?

I could probably google this but hey it’s a forum right? But how do we find out what caliber projectiles are?
I’ve found some old projectiles and am wondering what they are.
My best ill informed guess would be 50cal as they are from an old WW2 military firing range.
One weighs in at 668grains and another at 684grains. This could be due to corrosion, sediment etc
Photo of them next to 130gn 308 projectile.