On machine gun taxonomies

By 1930, the real world had pretty much sorted out what a machine gun was and what they could be, establishing the light/medium/heavy trichotomy that survives more or less to the present day (with adjustments for the GPMG.) Andalusada, however, is nowhere near as straightforward, despite having invented and adopted them pretty much on schedule, and having started a major war cycle (the Great War, most recently the Russian Wars) that really should have sorted this stuff out.

And because I've derped about this at length offline, I may as well take the opportunity to say why. And that answer is: It's France's fault.

Pre-Russian MG doctrine

The French Empire was an early adopter of the machine gun. Very much like the historic mitrailleuse, though, the French army considered and treated machine guns as a kind of artillery, not as a small arm; an unusual one, to be sure, but artillery nonetheless. I'm not totally sure why, having only outlined rather than written, but I can hazard a few guesses:

• Mounting. The Montigny mitrailleuse (very much like the Gatling gun before it) used a cannon mount that wouldn't look out of place in the Age of Sail, rather than the tripods we now associate with MGs. It was essentially a horse-drawn weapon. (IRL, that was why it had such ambivalent results: the French tried to use it for counter-battery fire, the same way they'd use a normal field gun.) I'm guessing that French machine guns in Andalusada more or less followed suit.
• Design. Militaries can be hilariously parochial - at least until the nonsense results in lots of needless, easily preventable deaths. (A lot of Cold War gun politics can be explained by the fact that the Pentagon simply did not want to have to admit that anybody else's ideas might be valid.) If the French MG was developed by, say, a panel of artillerists, it could very plausibly be branded "an artillery thing" from the start, coloring French MG doctrine for years.
• Caliber. That kind of office politics could also explain why French MGs were chambered for a different cartridge and caliber (8mm) than their infantry rifles (6.6mm.) (Andalusada's France went with 6.6mm for the same reasons so many European nations went with 6.5mm IRL, i.e. "the ballistics are pretty good now, and impossibly good in the black-powder age.") Nobody worries about horse artillery shooting something different from the light infantry, and this was a specialist weapon; why start worrying now?

At least originally, what excited the French most about the machine gun was the idea of a beaten zone. (A certain number of older officers are very fond of that sort of thing, and have trained with it until they can create precise and ornate patterns of lead in that zone.) And France, being a trendsetter for second-generation smokeless powder, set the trends that almost everybody else followed - which meant that the two-cartridge solution (and in particular the 8mm machine gun) became very standard across Western Europe.

After the Jura War

I know that the first major conflict where both parties fought with smokeless powder was the Jura War, triggered (if memory serves) because of an international incident involving a shipload of Swiss guns and a "consultant" or two getting seized en route to Surat during a war with the Sultan of Multan. The experience was like the Italians in Ethiopia, or the Japanese in Nationalist China: in most engagements, the great power's soldiers were consistently outgunned by opposing forces that were supposed to be noncompetitive. It was also the first time that machine guns (on the Swiss side) were seriously used for suppressive fire.

Part of the French response was to neck up their service caliber to 7.4mm, which was less of a trend but still went on internationally. (IRL, Italy was the only country ever to adopt a 7.35mm cartridge, but calibers being rather arbitrary there's no reason it couldn't take off elsewhere.) The other part was to start issuing more machine guns to the infantry, which is where the problems started - "more infantry machine guns" could be done in two different ways:

• Rifle-caliber MMGs: meant to be fired from a static position, but using infantry ammo for ease of logistical burden, meant to be organic; and
• MG-caliber LMGs: meant to be portable and used for short bursts, but logistically it'd lend itself more towards being part of the same artillery-company structure as the French MGs were, and attached.

Because it's the sort of dubious decision that a military would make, the French solution was to adopt both of them. Right in time for a colonial issue with England-Scotland to make the period "the Great War."

MG taxonomy after the Russian Wars

The lessons of the Russian Wars are still being digested, and there's no consensus as to what those lessons even were. (Warsaw School, I'm looking at you.) But there were some important technical developments to consider after it:

• The recognizable HMG: The Russian Wars, in particular the Thousand Days, saw the birth of what we'd recognize as modern vehicular warfare. With that came the rise of the first huge-caliber MGs, which eventually consolidated into a class of its own. (Andalusada's standard for "heavy" is "at least twice the caliber of your infantry caliber"; for some idea what that means, .50 BMG would be on the small side for the verse.)

As of 1930, "unitary" cartridges have been adopted in enough nations that the light/medium/heavy/HEAVY taxonomy of IRL is starting to establish. Not all of them have, though - sometimes because the unitary cartridge isn't there (the Japanese Empire in particular is having a standards crisis now that it includes the Meammosiran Cossacks), often because the designs proliferated. (Great Russia, in particular, has so many designs - field modifications, one-off wonders, the first fruits of a public education effort started under Evgeny IV, plus what they can manufacture with the machines they looted from Sweden - that there was military support for the Technical Census.) I'm not sure about how England-Scotland fares in this; but France, which did more than any other nation to make this headache happen, is definitely in the position of "too many designs blurring too many lines."

One thing I can see arising out of this, oddly, would be the French invention of the GPMG: a single machine gun, in a single caliber (rifle or not doesn't matter), designed to function in any role that isn't HEAVY. It'd be a hell of a shakeup if they did.

But that, it should be said, is for the future, not for 1930. And having reached the present day, I bring this post to a close.