Line-based calibers

As an American, calibers come in two varieties: Imperial, and metric. While there are some irregularities with the Imperial system (some .44s are actually .43 because they originally used heeled bullets, and anything may or may not have an extra .008" to allow for rifling), the Imperial system is blessedly devoid of any such. (Except, of course, for 8mm Mauser, which is 8mmJ or 8mmS.) Those two systems of measure - one of which I grew up with, one of which is intuitive - are the only ones that matter. Not so in Andalusada.

Sans decimalizing revolutionaries, France doesn't adopt the metric system. Sans France, nobody else necessarily does either. Up until the French Revolution, the world had worked just fine without universal metrication; there's no reason to think it couldn't continue to do so. (Except for France, and even that Augean stable doesn't need metrication.) And that means two, three, many systems of measurement - making my beloved gun porn a nightmare to write about.

But today, poring over two, three, many obsolete customary measurements, something clicked - and after doing some math, I found a beautiful heuristic in which to express calibers: for most of the world, smokeless cartridges are measured not by any international norm, but in lines.

The line as obsolete unit of measurement

The line is an old measurement. It was recognized in England in 1066 (half a generation before Andalusada begins), and judging by Wikipedia it apparently stayed in use across Europe until metrication.

So how big is a line? Beats the shit out of me. In the British Isles, a line was a quarter-barleycorn: ¹/12". In France, it was... a twelfth of a pouce, whatever that was locally. Where it gets complicated is in Central Europe; a Russian line was apparently 0.1 diuym (what that was I have no idea; Peter the Great standardized it to the English inch), and within the Holy Roman Empire it could be either 1/12" or 1/10".

To the best of my knowledge, the only army that ever used a caliber measured in lines was that of Tsarist Russia, who established a three-line cartridge for their service rifle. (In good fashion, they also sighted those service rifles in arshins.)

Line-based measuring leads to proven ballistics

Imagine my surprise and delight, then, to discover that certain magical numbers... naturally surface when you parse things in lines. Take, for instance, the pre-decimalization Danish line. What would be the caliber of a ball 3.5 Danish lines long? 7.21mm. Or a Norwegian line; three Norwegian lines would equal 6.55mm, an Imperial .25." Based on a nominal Saxon foot of 283.19mm, three "short lines" (based on decimal lines, so ³/120') would measure 7.07mm, three and a half 8.26mm - both only fractionally over the well-established .270 and 8mm of IRL. (Using long lines of ¹/144', three lines comes in at... well, just under 6mm, so too small for military use prior to the intermediate cartridge; but four lines would be 7.87mm...)

How much of this is coincidence, I honestly don't know. By the smokeless revolution, continental Europe (sans Russia, which used the Imperial inch) had metricated already; they also knew enough physics to calculate ballistics on paper, rather than through trial and error. (AFAIK, the only bore that wasn't chosen for ballistics was the American .30", which was set by Army Ordnance because it was divisible by 10 and would therefore make the math easier for engineers.)

But it's fascinating to me, how many proven bores can be generated simply by measuring in various local lines - absolutely fascinating. And more to the point, it's useful.

Line-based measures are easy and fruitful to copycat

The first modern smokeless rifle cartridge was the 8mm Lebel. It was like nothing seen before - and a lot of things seen after, because many 8mm cartridges popped up mushroom-like within a few years. The reason? Militaries favor proven technologies, especially ones that enable them to kill better - and in 1887, there was nothing like the 8mm Lebel on the planet. (Also, militaries generally don't like to get along, that being not their job; and this was the age of nationalism, when everybody wanted their own proprietary national caliber - even 8mm Mauser didn't go really international until the breakup of the Second Reich.)

During Andalusada's 19th-century smokeless revolution, similar logic leads (I declare, based on fiat) to an analogous but very different trend: nations copy relative bore sizes. I envision this playing out something like so:

• An initial nation (it's probably France) goes smokeless and beats the stuffing out of another state. Maybe they're using a line-based bore, maybe not (something makes me think that France does absolute measurements.)
• The beaten state, in turn, decides to modernize and upgun France, loudly adopting a "three-line" caliber.
• Other states, seeing the beaten party adopt a line-based caliber, adopt the same measurement, in lines, for themselves.
• At a certain point in this process, a customary system runs into insurmountable problems with this kind of copycatting. (Something like Norway or Saxony above, faced with something that's silly-small or stupid huge - although Poland-Ruthenia might do stupid huge. They certainly do postwar, after all.)
• Rather than saddle themselves with a bad gun, they instead adopt a different line-based standard, providing an example for further iterations of copycats.

I know, from established (though unwritten) development, that reinterpretations of absolute bore sizes happens all the time in the New World. Europe takes it a step further, making numerical bore sizes completely unnecessary. To condense this down to a further rule: most of Andalusada's Europe has adopted three-, 3.33- or 3.5-line service cartridges. These three measurements (three lines, three-and-a-half lines, or a third of an inch) will generate anything a European rifleman has ever fired in anger.

There are consequences to this, but that's for another day.