Modern Personal Defense Weapon Calibers 004: The 7.5x27mm FK Brno

An official image of the 7.5x27mm from FK Brno. Sadly, I do not yet own any specimens of this round.

It’s been a while since we’ve done one of these Modern PDW Calibers installments, but we’re back, and today we’re looking at a very new round on the market, one that is currently making some pretty big waves in the pistol world. I am talking of course about the 7.5x27mm FK Brno, designed for the CZ-75-derived FK Field Pistol from the company that shares its name. A high velocity .30 cal pistol round is not a new idea, having predecessors in the .300 JAWS, 7.62×25 Tokarev, and others, but what makes the 7.5 FK so interesting is just how powerful it is: A 103 grain monolithic bullet is advertised as leaving the 6″ Field Pistol barrel at an incredible 2,000 ft/s! This means that, if the company’s performance claims are true, the FK Field Pistol is ballistically the equal of the old WWII-era M1 Carbine!

The Field Pistol itself isn’t generally considered to be a PDW, but it does share several characteristics with the PDW concept as a whole, and FK has even developed an attachable folding shoulder stock for the gun. This does raise the question of whether some kind of pistol-rifle intermediate, maybe halfway between the Field Pistol and the B+T USW, wouldn’t be a good match for a round like the 7.5mm FK.

Onto the ballistics:

One of the things that will be a recurring theme in this series on PDW calibers is how difficult it is for high velocity rounds to match the downrange energy retention of even the humble 9mm NATO. Even the monstrous 7.5mm FK, with its 71% greater muzzle energy than the 9mm, only produces slightly more energy at 300 meters, despite the ballistic coefficients of the two rounds behind very similar. Matching the downrange energy of conventional pistol rounds like the 9mm and .45 presents problems for high velocity PDW rounds because of the dramatically increased drag of the supersonic flight regime. While .45 ACP is subsonic, and the 9mm becomes subsonic not long after it leaves the muzzle, rounds like the 5.7x28mm and 7.5x27mm stay supersonic for hundreds of meters, causing them to bleed velocity much more quickly as a result. With very low (in the case of 5.7mm) or only modest (in the case of 7.5mm) projectile weights, this means that after a certain distance these rounds will have shed their velocity advantage versus the 9mm, and therefore their energy advantage as well. For the 7.5mm FK, this isn’t a big problem as 300m is really the extreme end of its effective range, but the graph still serves as an illustration of this problem. For smaller calibers like the 5.7mm, however, low energy retention at moderate ranges is a real issue, and one of the biggest challenges I have found in designing small caliber, high velocity PDW rounds!

Since I do not have a 7.5x27mm FK round in my possession, I cannot say how heavy it is, but I can take a quick guess. The 7.5x27mm FK’s case is very close to that of the 10mm Auto, and its propellant load should be similar as well. I measured a 180gr (11.7 g) 10mm Automatic load at 17 grams per round, which gives us mass for the case + propellant + primer of 5.3 grams. If we add to that the 103 gr (6.7 g) projectile of the 7.5 FK, we get a per shot mass of approximately 12 grams, which in reality possibly shakes out to a little more – I wouldn’t be surprised to find that actual specimens weighed 12.5 or even 13 grams, depending on the mass of propellant and case wall thickness.



Nathaniel F

Nathaniel is a history enthusiast and firearms hobbyist whose primary interest lies in military small arms technological developments beginning with the smokeless powder era. In addition to contributing to The Firearm Blog, he runs 196,800 Revolutions Per Minute, a blog devoted to modern small arms design and theory. He is also the author of the original web serial Heartblood, which is being updated and edited regularly. He can be reached via email at nathaniel.f@staff.thefirearmblog.com.


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  • Wang Chung Tonight

    Is there a CIP classification yet?

    • micmac80

      In Europe nothing goes to sale without C.I.P: and yes cartridge is CIP aproved.

    • Hrachya H
      • Wang Chung Tonight

        Awesome, thank you!

        • Henry C.

          Getting a reamer made?

          • Wang Chung Tonight

            Just wanted to get some data. 43,000 PSI operating pressure. If it has small primer pockets. Just want the brass. To make crazy 9×25 Dillon loads. But I can and already do with reamed SSA 6.8 spc brass. It would be neat to shorten this case/cartridge a bit to fit in Glock 20 magazines. Shorten the dies to fit a new short case and oal. A 6.6in barrel with a compensator in a Glock 40 could easily match this 100gr 2000fps with the same proprietary 7.5mm projectile

  • RSG

    Will be a cool pistol primarily for the rich, or those willing to make large sacrifices to obtain. The pistol alone is going to be $5000. I can only imagine the cost of the ammo, as it’s only manufacturer is the folks who built the pistol. It is very unlikely to ever be manufactured by another ammo company.

    • Sulaco

      Bren 10 all over again?

      • Pumpkin King XXIII

        Nope, at least then bren 10 had Miami Vice to help sell it, it will never have the popularity and branding. This will far away with almost no examples produced like the Boz 224

  • LJC

    What is the pricing going to be?

    • You had to ask, so you can’t afford it.

      • Pumpkin King XXIII

        That not necessarily true, he may have the money but he’s not retarded and is financially responsible so he doesn’t want to up eating cat food when social security goes belly up.
        I mean it’s all about priorities, in college I ended up on a diet of Rama noodles for close to 3 months so I would buy a new 629 classic Dx With an 8&3/8″ barrel.

        • Jayste

          At least you had a beautiful 629 to shoot, when you could afford ammo. That’s what I may have to do (eat ramen noodles) if I don’t stop buying guns.

  • noob

    They need to make a cheap (think hi-point cheap) carbine for this. It ought to be legal for dear right? With such a short oal, the action length can be short also. Will it work with ordinary projectiles of lead or jacketed lead without getting projectile breakup?

    • I would not want to stand anywhere near someone firing a cartridge like this out of a carbine that was built Hi-Point Cheap.

      • DW

        Unless it is really a hi-point

        • Jayste

          They are ugly but pretty tough, my friend had one under his truck seat for a couple years, it fell onto the concrete more than a few times.

  • Bierstadt54

    I have hopes for this cartridge and I like the pistol, but I am not going to drop 5k on a pistol. Perhaps a US gunmaker will make something for the cartridge at a price point for the rest of us. Otherwise, it will be yet another boutique round for a boutique gun that only collectors own.

    • John Yossarian

      And more proof – with traditional cartridge design – there’s nothing new under the sun.

    • john huscio

      I’d expect glock to eventually have a model chambered for the caliber.

      • SPQR9

        That would greatly surprise me.

        • john huscio

          If it catches on even modestly, I’d bet on it.

      • They’ll come out with their own 7.5 GAP that’s 3.5mm shorter, and five years later when absolutely nobody uses them anymore, you’ll be able to pick them up LNIB for $200.

    • If there’s $5,000 of craftsmanship and performance in there, I’m sold. If not, my other “boutique” sidearms will continue to suffice. The price may also be a way to recoup the costs of development/importation/etc. It wouldn’t be surprising to see these drop to $3,500 (with a lesser finish) in a few years.

  • iksnilol

    What if we used a longer barrrel on it?

    Think M1 Carbine length barrel.

    • You’d probably be disappointed, since the propellant burn rate is almost certainly optimized for shorter barrels.

      • Jared Vynn

        It might be like 22tcm and pick up an additional ~800fps for an 18″ barrel. I think the larger bore would reduce the velocity gains of using a longer barrel possibly. Using the powley computer I was getting figures of an estimate of 2,400 fps for an 18″, but the computer doesn’t handle handgun cartridges or powders faster than 4227 well.

        • I am highly skeptical that the .22 TCM picks up 800 ft/s from an 18″ barrel.

          • Jared A. Faber

            Not 18″ but 22″ barrel pushes 40 gr .22 TCM to 2777 fps. Which makes a whole lot of sense, considering the fact that the .22 TCM pistols are infamous for their ridiculous muzzle flash.

            Velocity source: Rifleshooter

            Ps. Us Jareds have to stick together!

          • skeptic

            You should do some digging. Rated for ~1,900 FPS from handgun or ~2800 fps from a 22″ barrel. 800 fps seems reasonable.

          • That’s a gain of like 45 ft/s per inch of barrel, with pistol powder. I am skeptical.

          • Jared Vynn

            I had wrong barrel length it’s 22.75, and Richard Johnson covered an article on the rifle. It’s about 800 fps for an extra 17 inches roughly. Same factory loads as the handgun.

          • 22.75″, maybe, if you handloaded it with slower propellant.

          • Jared Vynn

            I believe factory ammo uses 22wmr powder, and most reloaders have used h110 and lilgun. I don’t have a rifle to chronograph myself yet, medical emergencies have taken priority.

  • CS

    I want to see SIG make an MPX for this caliber.

    • Ryfyle

      I wanna see What Keltec might do with it.

      • bmstylee

        An interesting plasticity thing that needs to be redesigned 3 times after going to market as it was not engineered properly. Then once it’s fixed they will make 3 a month. SOP for them.

    • Pumpkin King XXIII

      Hell, I would be happy if sig would just make the caliber swaps they said the mpx would have. It’s like 4 years latter ad still no 40 or 357.

  • ostiariusalpha

    Where did you get .160 G1 ballistics coefficient for the 124gr. M882 bullet? Everything I’ve read says it’s .149 above 1100ft/s.

  • Bernardo Costa

    Although I’m a bit skeptical of this round’s (weirdly plausible) capabilities, I’d love to see it tested and, perhaps, popularized. Seems like it holds a great potential if further developed properly and, obviously, well accepted by the firearms industry. Thanks for the great post, Nathaniel!

    • Thanks for reading, Bernard!

    • john huscio

      There’s video of a guy taking red deer (euro elk) with it.

      • Bernardo Costa

        Really? That’s impressive! Where can I find said video?

    • If there’s a big popular push behind it, I think it’ll definitely appeal to any 10mm fan. Brno needs to get one into the hands of a big action movie blockbuster star, post haste.

      • Bernardo Costa

        I endorse your words friend!

  • Disarmed in CA

    What 9mm pistol has an 8″ barrel?

  • Ballistic-Analysis

    Basicly its good to use a light fast round, but this time i think its just too much, a middleground would be more usefull. KE=1/2m x v² while p=m x v. Therefore a light projectile with high velocity has lighter recoil than a heavy with the same projectile. But i think the 7.5×27 exeeds the limit of a usefull middleground. Its Recoil is too high for a pistol with high % hit propability under stress.
    But some people here note that the gun is expensive anyways, therefore it might be not even intended for self defence, idk. Just my 2cents.

    • ostiariusalpha

      You should look further into the 7.5 FK Field Gun, it’s recoil is reputedly quite mild for the power of its cartridge.

      • Ballistic-Analysis

        Ofcourse, thats what i meant, im just saying you could further optimize a self defence cartridge. But i dont know if this is even intended for that role.

        • ostiariusalpha

          One of the early names for the pistol was the Combat Field Pistol, so take that as you may.

          • Amplified Heat

            It’s being ‘sold’ as a weapon for punching body armor, which obviously its long, skinny, projectiles traveling at high velocity are ideal for. Now in reality, it’s an impractically large gun for service (I think it’s just about Mk23 sized) and its excellent long-range ballistics are somewhat pointless seeing as it’s a handgun. But at closer ranges, it would certainly do a better job of defeating armor than anything but a true automag (and likely better than some of those), but I’d personally be wanting a stocked weapon for something like that.

          • ostiariusalpha

            FK BRNO seems to be directing their marketing almost exclusively towards sporting use for the pistol, it’s basically just us nerds that are considering its combat potential. And as Nathaniel has already mentioned in the article, it does come with a stock.

      • Amplified Heat

        That has more to do with it being both massive and enormous, though; neither of which are endearing traits for any kind of service weapon. Granted, it has the nifty recoil-damping weight inside it (in reality more of a rate-reducer, as seen in the PM63 PDW) as opposed to a simple lump of metal, but it’s still quite the imposing weapon.

        • ostiariusalpha

          2.86 lbs is certainly on the hefty end, but the Desert Eagle and AutoMag are about where I define massive for a handgun. Compared to other PDW SMGs like the P90 (5.7 lbs) or MP7 (4.2 lbs), having the whole unit (with stock attached) add up to 3.62 lbs isn’t an absurd weight.

  • Gary Kirk

    So, it’s pretty much a .30 cal .357 Sig with the proper parent case (10mm instead 40)??

  • Tassiebush

    I have a totally different role in mind but I really like the idea of something like this in a lever, pump or straight pull carbine in a super short action and with a real short barrel length. Should make for a very handy gun.

  • ozzallos .

    Measuring a personal defense rounds’ performance at hundreds of meters? I guess, but why? I’m sure it’s a super nifty round, but within “personal defense” ranges or even modern sport ranges, the cost vs advantage is going to be slim to almost zero. I mean, what are you doing with 9mm past 150-200y where this epic energy retention comes into play anyway? I guess it gives you a longer engagement envelope, but with a 31gr projectile? It screams ’boutique varmit round’ within the ranges its specified as being superior, not ‘personal defense’.

    That’s not to say I don’t appreciate the out-of-the gate horse power. But like you said, Tokarev and friends. I like me some laser rounds. And I freely admit i’m might very well be missing something here, but…

    • Brian Mead

      5-7 is pretty much the round nobody knew they wanted and nobody asked for, but they accepted anyway because they didn’t want to be mean and it looked okay at the time. It’s like marrying your first serious girlfriend because you’ve been together a few years and you just can’t rationally say why not and you don’t want to make her mad or go back to having an unwarmed bed.

      • Amplified Heat

        LOL, what? 5.7 was made in accordance with a specific request by NATO seeking to standardize rear-echelon weaponry across many nations, and they were nearly accepted but for HK’s queering the deal and the fall of the USSR taking off some of the pressure for an immediate upgrade. It was kind of the biggest ‘ask’ on the part of any military as far as small arms since WWII. In fact, it was so big that HK knew they couldn’t survive if they lost the contract to FNH, which is why they made such a fuss and kept the project from progressing (same thing as the US Tanker plane contract, same as joint strike fighter, same as the MHS contract will be)

  • Joe Deats

    A few thoughts, though my thoughts and a Buck might get ya a cup of coffee. That would be a fantastic SMG round, a longer barrel, more velocity, more spin for better accuracy, throw in a 30 round mag and some sort of AR15/MP5/AK74 small package and that’s a fantastic set up.

    The other thought is cost, most folks don’t throw around big bucks on hand guns, yea yea the occasional 2,500$ .45 but I think most people pay about a thousand bucks for a hand gun or less. I love the FK handgun it looks like it shoots well and is made well (though this is subjective right now as I’ve never used one) but the cost needs to be brought down.

    The round has possibilities, I hope it works out. The 10mm proves gestation times can take a while its just getting legs now (I own a 10mm Glock and love it, all hail the 10mm) so let’s hope this works out. I love interesting and yes niche rounds but the 7.5 doesn’t need to stay niche.

  • Colonel K

    I seem to recall the old 38 Super Cooper touched 2000 FPS using a 90 grain projectile and cut-down 223 brass fired from a 6.5″ 1911 barrel. I also remember the 110 grain 357 Auto Mag load claimed over 1900 FPS, and I think 2300 FPS was achieved when using a 90 grain bullet.

  • ChiptheBarber

    Somebody might have already covered this, but I would like to see the 7.5 compared and contrasted with more similar purpose rounds. Like 10mm, .357 mag, and .44 mag. Not a 31 gr projectile. I seem to remember one of the original articles I read on this gun/round was that it “hits like a .44 and recoils like a .40”. What’s not to love about that? I think there was even a video of a 100 yd one-shot-kill on an elk. As for the price point, I guess I’ll just have to wait for Taurus to come out with it in a $500 revolver! Yeah, I’m a barber.

    • Doctor Jelly

      It’ll be interesting to see how adoptance of this round progresses. Last I knew it’s proprietary, so no one will be making a chambering for it without paying royalties until FK BRNO relinquishes their rights and allows it to be standardized.
      But while I was instantly taken with with this cartridge when first announced (as it’s essentially a necked down 10mm putting out 30 Carbine performance), it would seem someone has mislead you with its felt recoil. According to FK, it’s supposed to kick like a 45+P, but that’s only in their handgun (which is big, heavy, and has a recoil mitigation system). So if it were in, say, a polymer based full size (about 2/3 the weight if we used a Glock 20 as an example), I have a feeling it’s going to quickly become too stout a kick to regularly shoot for us normals. Based off a quick Google for felt recoil charts, I’d estimate it may encroach on the recoil of a .454 Casull!