Les armes à feu spéculatives 2

That number is, of course, read as "deux". Guns post. Not all of them are directly sci-fi related, actually, but they all concern things that inform SF gun-thinking.

• Remember my musing about whether the USMC cadre of the Peacekeepers, in my SF, would use a bullpup rifle or not? (Either way it was still going to be a Stoner-like design.) Well, apparently, the trigger-pull issue? Doesn't exist with electronic firing. I should've realized it wouldn't.
  
  So now I guess the Marine gun looks a bit like the Bushmaster M17S, albeit probably not so 1980s. (It's still a Stoner rifle, a modified form of the AR-16 that was the predecessor of the AR-18, and therefore also of the Howa 89式 the JSDF use. It probably would, like the AR-18, still be short-stroke rather than direct-impingement, though; direct-impingement adds heat, which you don't want in a caseless design. The electronic firing, removing the issues of trigger-pull, probably makes up for any loss of accuracy.)
• Apparently, one of the interesting things about the "AKs are so reliable, ARs are crap" folklore, is, when an AK gets something in its gas-system (which can include rust, with old Russian-made or less-old Arab-made ammo leaving corrosive residue), it ceases to shoot. (Supposedly the way to clear it is to kick the bolt carrier. Like, literally. Apparently you often needed a hammer, though.) Know what an AR does, when something goes wrong with its gas-system? It becomes bolt-action.
  
  Apparently, AKs also jam if they start to overheat—and in even moderately sustained fire, they do overheat, not least because the forward grip consists of wood wrapped around the barrel (Soviet training preferred to avoid sustained fire; the nations they handed AKs out to like Halloween candy, though...). Wood is an insulator; apparently it will even start to smolder before too long, leaving you with a lovely birch-smoked hand (yes, I looked up what wood is most common for AKs) and a remarkably expensive metal-and-wood club.
• It occurs to me, the khângây might use small coil vulcans (or I guess rotary coilguns?) as their equivalent of an assault rifle or LMG. Presumably semi-auto fire, given their technology, has sufficient time between shots for barrel-wear not to be an issue. And I figure three barrels, like the M197 or GAU-19, might make assault-rifle rates of fire feasible (and I think the rotation would be recoil-operated, so the battery doesn't have to run the rotor as well as the firing).
  
  I figure they'll have a casing over it, like what sticks out of the nose of an A-10 Thunderbolt. Does a small-arms rotary firearm sound far fetched? It is overplayed, generally without reference to the real requirements of a machinegun of that size (though then again people ignore the realities of fixed-barrel machineguns, too). But, before you go saying it'd never be done, you may want to talk to E. C. Neal.
• I realize that Attack on Titan (which is actually Titan(s) of the Charge, given what "shingeki" means) is at least partly horror, so its plot necessarily runs partly on the Idiot Ball, but nevertheless, there are much more effective means at their disposal for fighting the things than leaping around on cables and chopping them with giant box-cutters. These people have cannons, so why aren't they using chain-shot? That'd quite easily cut a Titan in half, and if you point it so the chain passes through the weak-spot in the neck, it'll kill it in one blow, without anyone being anywhere near its hands.
  
  Of course, along with the Idiot Plot nature of AoT's horror aspect, is the "I don't care if it makes no sense, it's cool" nature of the action aspect. There are more efficient means of taking on Titans than the "3D maneuver gear"/giant box-cutter combo. Realistically, all but the biggest Titans would be little match even for men on horseback; you just have a few horsemen, working as coordinated pairs or small teams, ensnare the Titans' ankles, and then drag them over a giant version of "severe tire-damage" traffic-spikes, cutting through their weak-spot and annihilating them. And, since the Titans are the whole reason they live the way they do, they would've built giant traffic-spikes, and other anti-Titan defenses, all around the Walls, and into (at least) parts of the city streets.
  
  In real life, no one method of fighting—and Titans are basically armor without guns—is an automatic win, armor needs infantry support and infantry needs artillery; air alone is close, but you still need a diverse air force (something the "let's give the A-10's job to the F-35" people apparently don't understand). Titans would actually be only a minor inconvenience, at least for anyone who has guns.
• I think I've mentioned that zled space-forces are a branch of their artillery? They also have more ordinary artillery; as I said, they don't have our distinction between tanks and other guns, because their "tanks" are just up-armored self-propelled batteries that also have close-range attack capabilities. (I think zledo call them simply "armored guns"; we called a light-tank design project the "Armored Gun System", rather than, y'know, "light tank design competition", and unlike us zledo never used "tank", "cistern", or "reservoir" as code-names for "caterpillar machine-gun destroyers"—and they don't have "caterpillars", either.)
  
  Their artillery presumably does distinguish degrees of armor, among its guns, but also things like direct versus indirect fire, ballistic versus propelled (as in once the projectile leave the gun), and guided versus unguided munitions. I also think there might be a distinction between "fast" guns, on treads or spherical wheels (I think the spherical wheels give approximately the same performance as treads, but with an increase of speed and maneuverability), and "slow" or "all-terrain" guns, which are basically "spider tanks", with four legs. Hey, I said my SF had bipedal mecha, I never said all the mecha were bipedal.
• I really ought to go back to the Peacekeeper rifles' round being comparable to the .30-06, although it's still in a 7 mm package (rather than 7.62). Assuming each round weighs 10 milligrams (quite doable in that caliber if .270 Winchester and .270 Weatherby Magnum are any indication), and a muzzle velocity of 850 m/s, we get a muzzle energy of 3612 Joules. That requires a propellant load of 3.564 grams of nitrocellulose. 3.564 grams nitrocellulose is the equivalent of 1.497 grams of octanitrocubane, which has a volume of 726.699 cubic millimeters. If the propellant has the same diameter as 6.8 Remington SPC's brass casing (10.7 mm), and if we treat the 7 millimeter by 31 millimeter bullet as a cylinder, then we get a length to the propellant cylinder of 21.35 millimeters. It sticks out 1.85 millimeters in back (uniform thickness all around) and goes 19.85 millimeters up the side of the bullet.
  
  Given this, I guess we need to rename the thing "7 × 21 mm", rather than "7 × 18 mm". If each empty 60-round casket mag weighs 192 grams, and each round now weighs 11.5 grams (give or take 3 milligrams), then each fully-loaded magazine now weighs 882 grams. Compare that to the weight of seven STANAG 30-round magazines—each (taking into account that the M855 lead-free cartridge is slightly heavier than the old M193) weighs 486.3 grams—we find that, for only 3.6% more weight (3528 g vs 3404 g), each Peacekeeper can carry 14.3% more ammo—240 rounds as opposed to 210. And he only has to reload four times, instead of seven.
• Given the caseless rounds are only 32.85 millimeters long, it might be feasible to have the magazines load in the top—like those on the P90. FN 5.7 × 28 is 40.5 millimeters long, and we know you can use its magazines on an assault rifle (leaving to one side those who consider the P90 an assault rifle rather than a PDW or SMG). People do—there's a modified upper receiver for AR-15s that re-chambers them for FN 5.7 and lets them use P90 magazines. It's called an AR-57, or AR Five-seven (or presumably "AR Five-seveN", to those who didn't find that gimmick annoying in the pistol).
  
  One advantage, I think, to having the magazine where the P90 puts it, is you can see what your ammo-level is like (assuming the clear magazines so popular with the P90), without having to change your position. Most other magazine designs, bullpup or otherwise, force you to take your weapon off your shoulder to see where the mag-level is at, even if the magazine has clear sides. (Sure, you should keep track of how much you've fired, but what if you're handed a new weapon, or have to take one off a corpse?) Probably in real life, definitely in games, there are ways to mechanically or electronically indicate how many rounds remain—that counter on the back of the assault rifle in Halo?—but nothing beats being able to look.
• On the other hand, the sights on the P90 are a bit inelegant and unwieldy, 'cause of having to make room for the magazine. Might keep the magazine where it is ("normal bullpup", in other words) after all; I do have an awful lot of references to "casket magazines" that would need to be rewritten. Maybe use the P90 approach for the khângây small-arms coil-vulcan, though? That or helical magazines. Maybe both, under different circumstances—the helical ones would presumably be preferable for sustained fire/LMG applications, since they'd have less risk of jamming since they wouldn't have to rotate the bullet before chambering it. Ooh, yeah, I like that. And have the magazine under the barrel, instead of on top (which removes the "weird sights" issue). That probably means the bottom barrel is the one that fires, rather than the top like on our Gatling guns.