OK, so what are the factors of a weapon? In Venn Diagram, if possible. For example, here is what I have put together based on what I have gathered from this thread:
Cartridge Both Weapon
Length Diameter Distance between lands
Amount of powder (?) Distance between grooves
Heeled or not
Weight of bullet
There are straight-up 8mm cartridges (8mm Lebel and 8mm Nambu, to name two off the top of my head). There are also at least two 7.5mm cartridges as well - 7.5x55mm Swiss and 7.5x54mm French. (I know, not what you meant, but I thought it was worth mentioning).
Brand differentiation is also applied. The .300 Weatherby uses the same slug as a .300 Winchester, as does a .308 Winchester and a 30-'06. But all have slug diameters of around 7.62 mm. The .224 Weatherby also uses the same slug as the .223 Remington and the .222 Winchester.
Yeah, that’s a big part of it. The given NAMES don’t mean much. For example, the following are all considered 9mm:
Common name - Actual size
9x19mm Parabellum/Luger - 9.01mm
9x18mm Makarov - 9.22mm or 9.25mm
9x17mm (more commonly, .380 ACP) - 9.00mm
.38 Spl/.357 Mag - 9.10mm
.357 SIG - 9.02mm
.38 S&W - 9.20mm
.38 ACP/Auto - 9.00mm
But some of the interchangeability means parts can be reused, like when reloading.
Many more modern calibers were created by ways like: increasing the length of an old one (.357) or decreasing the caliber but keeping case the same size (necking down; e.g. .22-250 Remington [.250 Savage]; 7mm-08 Remington [.308]). A lot of the time it is due to a combination of convention and physics.
Actually, the 5.5mm socket is fairly common, it’s even part of some metric socket sets.
http://www.craftsman.com/craftsman-5.5mm-socket-6-pt/p-00943511000P
I’ve seen 5.5mm fastners used by automakers a fair amount, mostly on trim pieces, and seemingly mostly on American cars. Why? I really don’t know!
7/32" ?
It is very close, but 7/32" would be an odd size fastener to begin with, so I’m not sure of how exactly the 5.5mm fastener came about (as it gets used on metric-only cars). There certainly have been a few times that I’ve been quite glad that the 5.5mm socket has been in my toolbox, though. 
The reason I mentioned it was that I was using a 10mm to get my car battery out the other day, and found a 7/32" in the socket set. It’s not a very large set.
So…can we assume that a cartridge name is meaningless without more information?
For example I’ve been puzzled as to how a 5.56 (.223) round could be effective - although it obviously is… A .223 is only a tiny bit larger than .22 and having used a .22, it ain’t a knockdown round.
And today is the first time I learned that a 9mm is close to a .45.
Great thread.
It may not be obvious when you only look at bullet diameter, but when you compare the complete cartridges, there is nothing puzzling about it.
Yes, the name/number alone are useless for comparison. Here is a comparison photo of .22 LR vs 5.56 NATO (.223). Yes, the bullets are only only .003" different in size. However, the .223 cartridge has tons more powder and propels the bullet to a much higher velocity.
Oh. My. God.
Witness the hilariously named but scary .22 Eargesplitten Loudenboomer!
Th…this isn’t a joke, right? Guess not.
I can’t say whether the round pictured in the link is real, but there was an experimental round of that name.
It it appears to be real. That is a ton of powder behind a tiny bullet.
That is the point many of us have been trying make. People have invented literally thousands of different cartridges for their own use or to sell commercially and only a few are widespread. A couple of numbers won’t tell you what they actually are. That is an extreme case but it looks like a great way to fire a 22 caliber bullet incredibly quickly.
Just by doing some quick mental math, that has to be one of the fastest bullets in the world and I have no doubt that it is earsplittingly loud when it is fired.
Was going to chime into the thread earlier, but gave up. I recommend to Rucksinator that s/he check out a good reloading manual from the library (I’m partial to the Sierra Bullets’s one) and see the multiple dimensions that are measured for a given cartridge. And then go take up benchresting, and learn them in earnest…
My point with your quote though, Shag, is that I thought that burning nitrocellulose could only propel a cartridge so fast, no matter how much of it you used. IIRC, around 4150 fps (about the speed of some of the crazier .220 Swift, .17, or .22-.250 loadings) and to go faster than that, you needed a sabot. See the HARP project for how wild a gun in atmosphere could get. And then there are light gas guns… (Aside, isn’t Sandia Labs one of the most fun places in the world to work, for one’s inner 8 year boy that loves tosee things go “BOOM”?
Edit: a link that might be of interest, detailing some of the attempts to get higher and higher muzzle velocity in rifles and artillery.
The most recent edition of “Cartridges of the World” has over 1500 different cartridges in it.
Now, CotW basically covers almost every cartridge from their invention to the present day (with a few omissions), but it’s worth bearing in mind that there’s probably only a few hundred at most that are in widespread use (ie ammunition is still commercially produced in that calibre).
Personally, I wonder why people keep coming up with new cartridges all the time - surely we’ve got enough now to cover pretty much any scenario pending further developments in the small arms field?
