they don't call it a hand cannon for nothin'

The Colt Tennessee-Class.

Great! ...so now where am I supposed to get this? I mean that defeats the purpose of 'open carry!'

Slowest gun in the West.

But highest kill ratio per round!

I mean, 7.62mm in a handgun is also... optimistic.

This is why the US needs the metric system... like the rest of the world.

Also great for people who don't like loud noises, because it is usually fired remotely.

Let me introduce you to the obrez.

Hey Tokarev was a thing

so now where am I supposed to get this?

You can order yours at a naval shipyard of your choice. Unfortunately, due to high demand and supply chain issues, delivery might take a couple years, though.

7.62x51 sure. 7.62x25 tokarev no big deal

Add this elegant piece of furniture to your living room and fire your 357mm Handgun from the comfort of your sofa.

I got a little curious about calibers having these arbitrary weird numbers and tried converting them. So, 7.62mm is just 0.3 inches, and .357 is just 9mm, are they using the other system just to sound special or what? xd

Also neither .223 nor 5.56mm make sense to me, no idea what they are cooking

And great for target shooting, because even if you miss by dozens of metres, it's still a hit, if you're not completely unlucky, a bullseye, even.

Also great for people who don't like loud noises, because you'll only hear the loud noise once and never again

Even 38mm seems excessive. (1.49" for the primitives)

It's not that bad, but I can see why Walmart stopped selling 223mm and 357mm, because the weight of a single one of those will surely break a normal shopping cart when placed inside.

While the diameter is the same the heights and sometimes shape of the the bullet is a bit different. A .357 is significantly taller than a 9mm. This prevents you from using the bullets interchangeably even though the diameter is the same.

Silly metric conversions, everyone just calls it 14-inch shells.

But now that Walmart doesn't have them how am I gonna supply my King George V-class battleships?

One is thousands of an inch, which is a typical unit of measure for milling operations.
As the other person in this chain has said, ballistics is a weird game. End of the day, m(ass)*v(elocity)=f(orce), and the goal is getting f to a useful value. At that level, big and slow and small and fast have the same outcome.
But, because ballistics is bastard, other factors start to interfere.

For example, If you want to shoot farther, you can either go faster, or be lighter. Going faster requires more powder in the case, which creates a different profile for the round and changes the acceleration profile during firing (there are several rifle rounds over the years that have approximately the same load and bullet, but are ever so slightly different shaped, to change how the powder burns off and how it accelerates down the barrel)

Being lighter reduces your final impact force, and can impact stability mid flight (leading to alterations to the length and profile of the round itself)

Closer to the first point and tangentially related, the US has been a capitalist hellscape for a while, and has numerous instances of a company making a firearm using a new round because they did the math and said this is what we want and what you should want, followed by everyone else making more or less a clone of it if the gun in question sells well. Due to copyright it can't be identical, but as math goes, there a lots of ways to reach the same outcome.

Fortunately, me and the homies went shopping before this went into effect:

Amazon Prime...overnight that shit!

Short version of it is most of these names originated a century or longer ago in various parts of the world using different standards, the names have just been kept the same or shortened to the form we have today.

Take 9mm for example. Properly, it should be known as 9x19mm Parabellum, and was designed at the very start of the 1900s. There's a billion different "9mm" cartridges, some even with 9mm in the name, but 9x19mm Parabellum is so common everyone just calls it 9mm, because any other 9mm cartridge you could get is rare enough you have to special order them (like 9x18mm Makarov).

It was designed in Europe, so it uses mm. It has the same bullet diameter, but because .357 was designed in the US, it uses fraction of an inch in its name. At this point, they're essentially just used as names and not measurements, so they stay how they are. The distinction is important because they're completely different rounds and are not interchangeable, here's a pic of them side by sode:

With power assisted loading it's not that bad.