SF writer needs tips on low-caliber, high velocity weapons

Discussion in 'General Firearms' started by FilWi, Sep 22, 2020.

  1. FilWi

    FilWi G&G Newbie

    Hi everyone,

    I'm a writer and in my latest Science Fiction (a spaghetti western in space with magic) I'm doing a semi-realistic treatment of weapon effects (semi because, hey, there's magic!).

    I've got a 5 mm submachine gun that I want to penetrate, or at least visibly impact, a stainless steel bar stool. I'm imagining that with a high enough velocity, and the right bullet type, it might be possible.

    What say you all - can it be done? If not, what type of caliber/velocity/ammunition do I need?

    I'd like it to still be able to do the work of an SMG, i.e. something akin to an MP5 or PPsh, enough to be effective in semi-trained hands in an enclosed environment.

    Thanks in advance!
    Jaison likes this.
  2. runfiverun

    runfiverun G&G Evangelist

    high velocity will do the job without any fancy tricks or any magic bullet blessings.
    just get a 50 or 55gr. bullet moving along at close to 4,000 fps and it will easily punch through 1/4" or more of steel.
    the 22-250 and the 220 swift will both get the job done no problem.
    noelekal and TXplt like this.

  3. runfiverun

    runfiverun G&G Evangelist

    and just so you know I'd use the sci-fi moniker not S.F.

    S.F. means something/somewhere else [although it too has a touch of fantasy and 'magic' about it] and you just about got told something about 'muzzle control' and basic anatomy that nobody want's to hear.
    TXplt likes this.
  4. runfiverun

    runfiverun G&G Evangelist

    if you need something specific, I could probably design a small case size that runs at higher pressure to accomplish getting close to that velocity.
    something like a 30mm long 7.62 X 25 case stretched out and necked down would suffice with a lighter 40gr. projectile.

    since your in a sci-fi world you could just use a sci-fi type propellant to get there and that'd be your easiest out of the whole thing.
    you could cover the back story with a single paragraph or maybe two and move on to the story line.
    TXplt likes this.
  5. TXplt

    TXplt Gun Toting Boeing Driver Forum Contributor

    This might be worth a look (especially HEAT although from practical experience sabot might have been more effective in GW1):


    In getting through armor plate, there has been much development of rounds that essentially 'liquify' a metal slug (much like a type of fast acting powerful acetylene torch) in real time to make it cut through the metal and into the interior. This is one way as is steel or heavier metal cored slugs which use more the sabot concept.

    As rounds get faster their qualities in doing this (i.e. liquifying due to kinetic heating) become more significant due to kinetic heating when they hit something. Many of us shoot at 3/8 to 1/2" steel plates for recreation (the bullet breaks up safely when it hits a dead-flat hardened steel plate and these are sometimes angled so that fragments go down or in a specific direction. It's POSSIBLE to get a bad bounce on low quality or spalled steel but usually unlikely for most rounds shot at them). There's a minimum safety distance depending on round. Anyway, most AR-500 or 550 steel has a recommendation/requirement for maximum velocity on impact DUE to the fact that kinetic heating above this velocity can damage or spall the steel (increasing the chances for a bad bounce or bullet fragments going where you don't want them to).

    To make your concept feasible you'd need to get something of high enough velocity while still having enough mass to reek havoc on the other side.

    Hyper-velocity driven by conventional powders isn't an easy thing (the .223 operates at around 55K psi -- which is relatively high -- but some variants go into the 60's or perhaps even 70s--and that delivers around 3200 FPS (full length barrel--on a 10.5 or 11.5 inch upper this drops to the mid-2000s) for a 55 grain bullet or around 3000 fps for something in the 60's; a grain is 1/7000 of a pound). The higher pressures induce additional stress on the operating components (particularly in a semi) and timing/dwell time/bolt lug stress issues, etc. all go up. And it takes a whole bunch MORE powder to get from 3000-4000 (it's not linear) in that drag and friction all go up as either the square or cube of the velocity depending on what it is and who you talk to (i.e. exponentially). So getting to hypervelocities in light, portable, semis (or full auto) presents some unique engineering issues.

    As has going to shorter barrels in M4s while trying to replicate performance of longer barrels (it's kind of the same concept).

    To get around the (outdated) Geneva restrictions on using FMJ ammo, the .223/5.56 was designed to destabilize when striking a target (essentially fragmenting and dumping its energy into something) when used at closer ranges; the bullet design being analogous to a tailwheel airplane vs. a nose wheel one when hit by a gusty crosswind (on a tailwheel airplane the gust tends to exacerbate the swing and can cause a ground loop if not corrected by the pilot by rudder and/or brakes).


    FWIW, the 50 BMG has decent performance but is a big gun and cartridge:

    Last edited: Sep 22, 2020
    Jaison likes this.
  6. BigEd63

    BigEd63 G&G Evangelist

    First of all most bar stools aren't armor plates.

    I've seen a freaking BB Gun dent an old steel helmet because I'm the one that did it.

    I've also put .223 SP 55gr through 3/16"mild steel at 25ft. Velocity approximately 3100fps.

    Submachine gun or Handgun -something in .22TCM with penetrator rounds and alternate magazines for frangible loads aboard a ship as hull breaches can be a bad thing.
    Don't want to take off and run with your idea but thought I'd toss out some other possibilities. Selector switch in Safe, Burst (3-4rds) and Rock and Roll.
    I'd even go the top feed FN 5.7 route with 50rd magazines that fit flush. CQB in space can be very tight after all.
    Slim sleek design. In fact the handguard could be the magazines. Push button rotate handguard 180degrees charge and fire!
    2 50rd mags with a total of 100rds on board. Mags changed by pulling back on spring loaded recessed tabs on magazine near the muzzle. In fact the rotating handguard/magazine holder could be used to switch quickly from penetrator rounds to frangible ones
    Okay enough of my rambling.
    MosinRuger, TXplt and Jaison like this.
  7. Big Dog

    Big Dog Retired IT Dinosaur Wrangler Forum Contributor

    No need to over think this. Are you penetrating a sheet steel structure, or a simple SS tube (stool support)? In either case, a . 223Rem/5.56X45.. FMJ round will penetrate easily. Even the 5.7X28mm in a PDW should have no trouble penetrating these structures. They aren't armor.
  8. FilWi

    FilWi G&G Newbie

    Wow, you really are the friendliest gun forum on the web :)

    Big thanks for all the info, and I just might run with the dual flush 50rd magazines. It's the details that do it! :)
  9. Outpost75

    Outpost75 G&G Evangelist

    I always thought that a cowboy shoot-out in which somebody improvised steel fleshette rounds in a 12-ga. double, blacksmithing the heads of iron nails to produce "fins" so that they would be stable, than blowing the bar room to flinders would be great entertainment.

    Bar-shot connected by a chain and simultaneously firing both barrels could be synchonized only in the movies, because when the Confederates tried it with cannon they wiped out two gun crews...

    And of course you could have gun powder mixed with opium which produces smoke to make the bad guys compliant so that they could be easily arrested...

    More ideas in the old Kung Fu series were lost on the cutting room floor...
    Ranger4 likes this.
  10. Ranger4

    Ranger4 G&G Evangelist

    A common steel BB is 4.5 mm. In duck loads they normally travel 1,300 fps at 25 feet from the muzzle and a 1 and 1/4 ounce load would have 90 BBs in it. A steel BB at 1,300 fps is far different than your typical BB gun at 450-600 fps. Depending on the strength and thickness of the bar stool steel, which would not likely be heat treated or overly strong, I would think even one 12 gauge round would "visible impact" your bar stool. Even better just shoot it with standard 00 Buck. You might be surprised.

    The new 5.7 x 28 Ruger handgun regarded as a speedy little bullet only produces about 220 foot pounds of energy, a 12 gauge 00 Buck produces about 1,600 foot pounds, that will put a visible impact on a bar stool. In fact, any 9mm ball ammo should penetrate bar stool metal. I have seen many from a sub machine gun penetrate and entire car, both doors, door paneling and all landing somewhere in the world beyond the car. IMHO
  11. runfiverun

    runfiverun G&G Evangelist

    impact to a bar stool would be an understatement.
    I have made some high BHN 32 cal. buckshot loads that'll penetrate an old school freezer both sides and keep on zinging off into the dirt.

    if you look at the old [90's type old] Cobray guns they have a unique magazine setup you might be interested in.
  12. runfiverun

    runfiverun G&G Evangelist

    oh one more thought.
    if you want you could make the gun a revolver, and chamber it in 22 Casull.

    that is a 454 Casull round necked to 22 caliber and is run at the high pressure of the Casull round.
    it will zip a 22 cal. bullet out with enough speed to easily cut through 1/4" stainless steel at bar room distances.
    [freedom arms model 83]

    call it whatever you want, Dick won't care he only made a pair of the handguns, and he has been dead for 10 years now.
  13. MosinRuger

    MosinRuger G&G Evangelist

    .22 tcm or 5.7x28 would make good penetrating SMG/ pdw rounds.