I wish the author would mention the odd reason why we now call a 36 a 38 and where the .357″ diameter came from. That was the heel diameter for the original 38 Long Colt which had a major diameter more like .380″. It was similar to our 22 LR which uses a heeled bullet roughly the same diameter as the outside case diameter.
The 38 Long Colt was used in 36 caliber percussion revolvers bored through to take metal cartridges (back then still going strictly by bore diameter rather than groove diameter). So the major bullet diameter was close to .380″ and bore close to 36, but since the case had to fit the original chamber diameter, the bullet heel was made to around .357″ to fit inside the case which in turn fit inside the original 36 percussion chamber of around .380″.
The heeled bullets had the lube groove exposed outside the case, and that became a problem when handling loose cartridges, so when manufacturers started making guns designed from the ground up to use metal cartridges, they used the same cartridge case, reduced the bullet’s major diameter to the .357″ heel diameter, eliminating the heel, and used a smaller bore.
And that is how we ended up with the “38” cartridges, based on the 36 percussion revolver, which use a .357″ bullet.
A similar progression took place in regarding the 44 percussion revolvers. In that case cartridges split off to become the modern 45s and the modern “44” which takes the .429″ bullet based on the heel diameter of the 44 Colt cartridge used in conversion revolvers.
That’s also how we ended up with two different “45” diameters; the original (I would say “true”) 45 which uses a .458″ bullet, and the 45 that grew out of the 44 percussion revolver which takes a .451″ bullet and is actually a “44” by 1860s standards.
Here’s another bullet, showing the genesis of our modern “38” caliber designation. Notice the major diameter of .375″ , the heel diameter of .357″ and the outside-the-case lube groove. It’s for the 38 Long Colt cartridge, to be fired in a converted 36 caliber percussion revolver frame and barrel having a bore of .36″ and groove diameter of .375 to .380″ http://accuratemolds.com/bullet_detail.php?bullet=38-135C-D.png