[ur-whale]

From an engineering perspective, I've always found fascinating how complicated ammo taxonomy is and how weird the various units used are.

I get the historical aspect that led to this giant mess, but ... at the end of the day, there's not that many parameters to define what a bullet is and does.

In particular, wrt physical dimensions, my - probably naive - take is that (radius x length) seems to go quite a long way in describing a bullet.

Anyone more knowledgeable care to explain why things are so complicated and haven't been normalized / simplified over time?

[colechristensen]

I was once called an expert in external ballistics, this may have been an overstatement but I did spend quite a lot of time writing simulations for the ballistics of various bullets.

There are three phases that are important for bullets: what happens inside the barrel, what happens outside the barrel, and what happens when it strikes the target.

There are a lot of parameters effecting that characteristics of all three. (not just 2 dimensions of size)

Shape, muzzle velocity, reliability, ease of manufacture, etc etc. are all quite important.

There is also long history, a gun is a thing that can be around for decades; you can't so easily throw away the past and start over. There is also a strong consideration for the design process. Fulfilling a set of requirements can conflict with the desire for standardization. Also when standardization is an idea, using an existing standard rather than making a new one has been the pragmatic response.

NATO though has done quite a lot in standardizing American rounds. There are many almost-equivalent NATO standard rounds with things like metric measurements instead of the more historical American measurements.

But also, things are just complicated. When talking about an airplane you might as well say that length and wingspan might "go quite a long way" in describing it. I mean, in some sense sure, but a very long way from fully describing one.

There's a book "American Rifle" which goes through quite a bit of the history of the development of guns in the US.

[collegeburner]

Because there's a ton of organic growth over more than a century and a shitton of holdovers. Think of it like really old legacy systems in computing.

Like look just at naming: old stuff was often named based on caliber and the number of grains of powder back in black powder days. Like the .45-70 is a .45 bullet and had 70 grains of black powder in a standard load. But then this carried over when they named the .30-06, which had a .30 bullet and 6 grains smokeless. Some handgun rounds are "ACP" because they were developed for new (at the time) auto-loaders instead of revolvers. Now cartridges are mostly named by caliber.

Then there's stuff where cartridges were slightly tweaked, like for NATO. .223 is mostly the same as 5.56 and .308 is mostly the same as 7.62, but the latter are both NATO rounds re-named and changed a bit from their predecessors. Oh and by the way, .308 rifles can typically fire .308 or 7.62, it's not safe to fire .308 from a 7.62 rifle though. Oh but for .223/5.56 it's the other way: You can fire .223 from a 5.56 chamber but not vice versa.

Every country developed its own rounds for a long time, just look at the number of 9mm cartridges there are. Different bullets, different nomenclature, etc.

There's a ton of variety in how you make a bullet, even beyond "broad" varieties like hollow point vs jacketed vs semi-jacketed vs wadcutter vs semi-wadcutter... or the actual metal composition of the bullet, jacket, etc.

Different rounds are also loaded differently, you can have some under-pressured for subsonic if you're running suppressed, there's usually some variation in what's "standard" and bodies like SAAMI and CIP are voluntary and typically define max pressure only. Plus there are overpressure (+p) and over-overpressure (+p+) rounds...

Lots of complexity from over 100 years of a lot of people developing their own ideas than merging them only sort of.

[nataz]

You have to go one layer deeper and think beyond the projectile (bullet) and include the cartridge (bullet, accelerant, primer, case).

Basically how fast some thing shoots (how much accelerant) is just as important as what you are shooting (bullet characteristics).

Each of those variables also have weight and dimension penalties which determine how much you can reasonably carry.

An interesting relatively recent example is the development of small caliber armor piercing rounds. NATO needed something to deal with the rise of body armor. Same requirements, two different solutions to get there in the fn 5.7 and hk 4.6x30 (simplifying enormously here). Basically these are engineering and manufacturing challenges.

[collegeburner]

For anybody who hasn't heard of them and wants a rough overview of the differences, the 5.7 and 4.6 mostly work on being smaller-caliber at higher velocity. 9mm parabellum usually has muzzle velocity anywhere between 1000 and 1500 ft/s where 4.6 is closer to 2300 ft/s. The 5.7 is closer to 2800. They're also usually steel core.

[ggreer]

I'm pretty sure all the steel core 5.7x28mm is considered armor piercing handgun ammo and is therefore limited to law enforcement.[1] I've never seen steel core versions of it sold at any gun store.

1. https://www.atf.gov/firearms/docs/open-letter/national-jan20...

[collegeburner]

Sadly yeah, it's one in a massive list of stupid laws but FOPA states anything that "may be used in a handgun" if I'm remembering the wording right. I believe they submitted the duty round for the NATO RFP tho and that's steel penetrator. If i remember right blacktip .223 is similarly banned because of AR pistols, you can basically only get AP in full rifle rounds (.30-06) or something like .50 BMG.

[bjt2n3904]

> there's not that many parameters to define what a bullet is and does

There's a surprising amount of parameters that define what a bullet is and does. Consider this article, which describes the difference between secant and tangent ogives.

From an engineering perspective, long range shooting is FASCINATING!

http://bulletin.accurateshooter.com/2011/03/tangent-vs-secan...

[sigstoat]

> In particular, wrt physical dimensions, my - probably naive - take is that (radius x length) seems to go quite a long way in describing a bullet.

that doesn't describe much of a bullet, and nearly nothing about a caliber.

you can take a look at the SAAMI specs and get a sense of what goes into such things.

https://saami.org/technical-information/cartridge-chamber-dr...

the popular name of a caliber is exactly that, a name, and describes the caliber about as well as "John" describes a human being.

[0x7E3]

For the bullets themselves, in addition to the diameter and length you've got mass, material and shape (round nose, hollow point, ballistic tipped, etc.).

For the cartridge as a whole you're also going to be concerned with powder capacity, shape (necked?, rimmed?), and to a lesser extent material.

These are just a few examples and all are significant.

[akerl_]

What would the upside be in “simplifying” it? At present, there’s a known set of standard ammo sizes in use, and millions of guns in existence that use them.

Sure, the nomenclature is weird, with a mix of imperial, metric, and just plain weirdness, but it doesn’t seem to be negatively impacting anything.

[paisawalla]

I think this is yet another area where large budgets and low accountability creates "innovation" primarily in how to spend public money. Large police and military budgets create incentives for manufacturers to innovate away from the standard and introduce "high performance" proprietary form factors.

In some cases a new round size/weight does actually produce better performance for the desired application. In many cases, IMO, those advantages are academic and achieved in highly controlled environments, i.e. they are nullified by the high variability of other factors, in real world situations. I am just an enthusiast and not any kind of professional though.

[sigstoat]

> Large police and military budgets create incentives for manufacturers to innovate away from the standard and introduce "high performance" proprietary form factors.

extremely few of the calibers out there have ever seen military/LE use, and fewer of them started out with military/LE use.

[paisawalla]

If you're considering the full history of ammunition going back over 100 years, then yes. But if you limit yourself to the most commonly stocked ammo types that you would see in a store today, which would include

- 9mm

- 10mm

- .357

- 40 S&W

- 308 winmag

- 5.56

- 7.62

then no, these are most (all?) cartridges that began life with LE or military application. Even many of the less common ammo types that are still not unusual to see stocked, or seen at the range, like 300 blackout or 6.5mm Creedmore also start life as RFPs from military or LE operators.