Garand barrels in 7.62x51 nato

[Cosine26]

Thanks for the answers
Using the measurements provided by “mdoerner, I made the following calculations:
For the 30-06- 0.0790” the area of the port is 0.0049 Sq In
For the Army 7.62-0.105”, this is 0.0087 sq in or a 76% increase in port size.
For the Navy 7.62 – 0.1065”, tnis is 0.0089 sq in or an 81% increase in port size
These seem to be quite drastic changes. Were they computed or developed empirically?