Durango Dave.
By now you've realized the vastness of your questions. Besides everything posted above, there are some basic realities to know and understand:
1. Like any subject there are short cut nick names and just plain misnomers. For ex.: we don't load 'bullets' into guns; we load 'cartridges'. A 'cartridge gun' uses a self contained cartridge made up of a case, bullet, gun powder and primer.
2. Many cartridges are very similar to other cartridges using the same caliber bullets, therefore manufacturers use arbitrary cal designations to differentiate between the different cartridges: .22s probably have the most variation of cartridges. And all shoot a .224" caliber bullet but can be labeled, .22, .218, .221, .223, etc., etc. Usually with various descriptors attached to differentiate them: .22 CB, short, long, or long rifle, .218 BEE, .221 Fireball, .223 Remington and several more because these cartridges range from rim fire to center fire and from 1/2" tall to 3"+. One reason is safety so someone doesn't try to load just any of those .224 cal cartridges in just any .22 cal. gun!
3. Most all common cartridges used today have evolved from round ball caliber sizes of the percussion era, to heeled bullet sizes that followed, to the modern Inside Lubricated bullets.
4. Actual bullet diameters, and barrel bore and groove diameters are not an exact science but work safely with small diameter variations. But in order for a lead bullet to be accurate it must always be a bit larger than the bore diameter and even .001" over the groove diameter (less for jacketed bullets) for a good grip in the rifling to obtain its spin!
The bottom line is that every cartridge has a different story as to how it ended up what it's called today. So as you can imagine, each of those different stories cannot be answered here in a post, they fill a book and must be read.
One very good inexpensive book reference book is the soft cover "Barnes Cartridges of the World", about $15. No one reads the entire book! You just look up the cartridge or cartridges that you are particularly interested in, and read that paragraph.
Hope this helps