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My setting is set around the 23rd century, and for my military, I was wondering what kind of sidearms they’d use. After searching, I found something interesting: there are pistols chambered in 5.7x28mm rounds (which were originally made for PDWs such as P90s and MP7s).

I was wondering, would it make sense for a military to adopt sidearms chambered in 5.7mm ammo, and what reasons would likely lead them to doing so?

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  • $\begingroup$ most PDW's already chamber pistol ammunition , and 5.7x28mm rounds is a pistol ammunition so what exactly is your question? $\endgroup$
    – John
    Jun 18 '21 at 0:05
  • $\begingroup$ You will probably have to reason out the specific circumstances that lead to cased ammunition still being used by militarizes in the 23rd century given recent developments with polymer cased rounds and even caseless ammunition. The simplest might be that warfare is entirely automated and AI driven with humans being strictly 'rear echelon' and therefore rarely involved in direct confrontations with enemy. So they get issued with PDFs & AP rounds for taking out bots. PDFs were specifically designed for issue to and use by rear echelon troops to begin with. That might ruin your story though. $\endgroup$
    – Mon
    Jun 18 '21 at 0:48
  • $\begingroup$ Worthiness as a weapon aside, I suspect the answer will typically be "the politicians who sign off on your budget got kickbacks from the manufacturer/wanted more jobs in their district/wanted to prop up their nephew's company". $\endgroup$
    – Cadence
    Jun 18 '21 at 0:50
  • $\begingroup$ @Mon: I’m talking about the bullet itself. The cartridge can be whatever. Also, no, humans still make up the majority of the military $\endgroup$
    – DT Cooper
    Jun 18 '21 at 1:07
  • $\begingroup$ Then probably no (apart from rear echelon troops as discussed previously). Unless you greatly increase the amount of propellant i.e build an entirely new cartridge) for the same bullet there's no real point (and that can have undesirable ballistic effects). Armies want range as much as penetrating power. Also the caliber/muzzle velocity/mass/materials used in a bullet are going to be dictated by the amount/type of armor worn by the enemy and the ranges they typically expect to engage them at. And whatever that range they'll want the best ballistics they can get. $\endgroup$
    – Mon
    Jun 18 '21 at 1:44
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5.7x28mm is what the FN Five-Seven pistol is chambered in, and if I'm not mistaken, the 4.8x30mm round made for the MP-7 was also planned to be put into a pistol, although that project was cancelled because the round supposedly didn't provide amazing ballistics when utilized in a pistol.

It's the same case with the Five-Seven. It's a fine pistol, but it can't get the same performance due to the short barrel length. It still performs better than typical rounds like .45 ACP and 9mm parabellum.

There is no real thing as a PDW round, since PDWs are, by description, primarily chambered in pistol rounds. They just tend to have longer barrels, faster muzzle velocity, and a higher rate of fire than a typical pistol.

To me, personally, I think there's an advantage to having your standard PDWs to be chambered in the same rounds as your pistols, because the pistols are still better at military aspects like penetration, and on the production side it simplifies things so you're only producing 1 product as opposed to multiple.

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In the 23rd century?

Standards like ammunition have remarkable longevity because you often design weapons for existing ammo, or slightly improved ammo for existing weapons. Still, over two centuries are a long time to assume that a late 20th century round would still be in use. That would be like finding a Land Pattern Musket in combat use today.

So the two related questions are:

  • Would they still use firearms with chemically propelled, cased ammunition?
    Laser pistols might be available, or they run into problems of energy storage, heat management, etc., and remain a niche weapon for niche applications. Same for railguns. But how about liquid propellant or caseless? Those might be good replacements for conventional, cased ammo.
  • Would they use projectiles around 5.7mm with a PDW-like shape instead of shorter, fatter projectiles around 9mm or around 11mm?
    Possibly. Especially if they go for liquid propellant, PDW-style ammo could be much smaller, which allows more shots in a not-too-long magazine. With the right materials, they could be better at piercing armor, which leads to the question just how common body armor is in your setting.
    You could assume that all soldiers routinely wear armor, and either pistols are history because they're ineffective, or the only remaining pistols fire low-diameter rounds. Or you could assume that the proliferation of gadgets and gizmos leaves little weight for armor, and sidearms still work.
    • Side note: How about exotic environments?
      In space, a single tear in the space suit can be fatal. That could encourage 5.7mm-like rounds over .45-like rounds.
      On a dusty planet, at the end of a lightyears-long supply line, do you want a simple, reliable handgun with metal-cased ammo, or something like a laser pistol that can be recharged from a solar array, or perhaps a caseless pistol combining relatively light ammo with relatively easy maintenance.
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  • $\begingroup$ Well... We do have the Mosin-Nagant still in limited service in the world. 1891 design, original cartridge was black powder (very much like .303 British) but built with expectation of switching to smokeless. It's about as old as a rifle can get and use modern-ish ammunition. The Mosin is the longest serving military firearm in history to date, and it wouldn't surprise me to find them still in limited service on the 150th anniversary of the original introduction. $\endgroup$
    – Zeiss Ikon
    Jun 18 '21 at 14:16
  • $\begingroup$ @ZeissIkon, good point, but how much would you bet on another 100 years? $\endgroup$
    – o.m.
    Jun 18 '21 at 14:20
  • $\begingroup$ In service like Afghan rebels or sportsmen, I'd bet heavy. You still see 1903 Springfields, and they've been out of military service for 75-80 years. It's a robust, wear- and grime-tolerant design, with ballistics similar to the current 7.52x51, and there are literally tens of millions of them around. It was the most produced rifle ever, until the AK-47 surpassed it a couple years ago. $\endgroup$
    – Zeiss Ikon
    Jun 18 '21 at 14:23
  • $\begingroup$ @ZeissIkon I own a 1944 mosin :) $\endgroup$ Jun 18 '21 at 16:46
  • $\begingroup$ @Haveaniceday Mine is 1942 Izhevsk. $\endgroup$
    – Zeiss Ikon
    Jun 18 '21 at 17:16

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