5.7×28: The Ultimate Survival Caliber? (w/Video)

A tag team I never would have expected

Bear with me friends, this week’s gun review is going to be a little off the normal structure. While the firearm we chose to use is important, the bigger picture, in this case, is what that means for the caliber. The previous sentence should actually read firearm(s) because it is two in tandem that really makes the case for what I am proposing as a radical departure from the norm in survival calibers.

CMMG upper on the test lower

From the picture, you can no doubt tell we got our hands on a CMMG AR-15 upper in 5.7x28mm. And like all the other CMMG products I have reviewed, it is absolutely fantastic. If you are a long time reader, I don’t have to tell you how highly I think of the CMMG 300 series firearms. I have already done so here, here, and here.

Leupold Freedom RDS

Just a few notes on the upper, before we get to the meat. I don’t mean to overlook the CMMG engineering here. It is amazing and has all the awesome features of the other CMMG products we have reviewed. Our test model was a 16.1 inch upper in Burnt Bronze cerakote, one of the 12 free cerakote options on any CMMG product. Instead of a gas impingement system, the Mk57 upper uses CMMG’s patented radial delayed blowback system. Just like on the 10mm pistol, it reduces recoil significantly, as well as runs like a sewing machine. Due to the lower pressure of a 5.7mm round, the bolt is skeletonized to reduce weight. And par for the course, it includes CMMG’s oversized Ambi charging handle. It’s fantastic, as has been every other CMMG product we have tested.

Oversized CMMG charging handle

But the real story here, to me, is what this means for the cartridge. Especially when combined with a new handgun from Ruger last year, the Ruger 57. Either gun, by itself, pretty cool I will grant. But neither alone really enough to convince me to relook 5.7x28mm. But together? Now we are starting to look at a system that has the potential to turn survival caliber debate on its head.

Besty’s in 5.7x28mm

Let’s start with the ballistics data, as that is particularly relevant to this discussion. 5.7x28mm from a pistol length barrel (The Ruger 57 has a 4.94-inch barrel) is fast, but not what we would call staggeringly fast. To deep dive this, we have to first take a step outside of our current gun discussion and address some terminal ballistics theory.

Skeletonized 5.7 BCG vs standard 556 BCG

Now I say theory because terminal ballistics or wound ballistics is not a settled science. If it was, we would all be running a single caliber by now, military included. There has been a lot of testing, and a lot of debate, which does give us a starting point. We also have a lot of real-world experience shooting humans over the last 20 years, which matters too. But at the end of the day, we all still have to make our own decision. My take on the 5.7x28mm is fueled by my combat experience and what I can ascertain from scientific data, but a lot of it is still an assumption. While all that experience bit is real, the fact remains 5.7x28mm hasn’t seen much if any battlefield use, at least not by anyone I have met. So let’s call what I am going to say next an educated guess, very much open to new data.

A bolt face best described as cute

In the great debate as it pertains to small, fast projectiles we come across two mechanisms of wounding. And you can go down some serious rabbit holes here, starting with Dr. Martin Fackler. The first principle is what is called a temporary wound cavity or secondary cavitation, depending on your preferred verbiage. The idea here is that the velocity of the projectile directly affects how much tissue stretches away from the point of impact. Tissue being largely water, it reacts to a high-velocity missile much like the ripples in a pond. You can see this in anything from a boxer hitting another boxer, to the flex of a gelatin block with a bullet. The principle is that the water/tissue flexes away from the impact, pushed not only by the force of impact but the air being dragged along by said projectile, especially in supersonic flight.

Note blowback vs DI carrier key

Where this theory gets dicey is in how much it matters. No one, ever Dr. Fackler, debates that it happens. But there are competing claims about how much it matters. Dr. Fackler theorized that secondary cavitation meant almost nothing, as the tissue usually just stretches and returns to form with minimal damage. Later theorists, however, dispute that. The second theory is that secondary cavitation does matter, provided the incoming projectiles speed is high enough. The idea here is that below a certain threshold of about 2400 fps, the tissue is undamaged. But above that threshold, the tissue stretches so much that it is actually torn and damaged, producing wounds all out of proportion to the size of the bullet.

556/223 vs 5.7

The second theory of wounding comes from the principle of fragmentation. The idea here is that if you push a bullet fast enough it will come apart when it impacts tissue, as the g forces on the yaw of the bullet snap it apart into multiple smaller projectiles. Each with their own wound path. ( Yaw can be simplified like this. Bullet is flying nose forward toward tissue. The nose hits the tissue first, and therefore starts bleeding speed first. Like a car wreck, the rear of the bullet has not had time to slow down as the nose impacts. So as the bullet is penetrating tissue, it is also flipping over. In high quality ballistic gel you can often see this. Small wound path, a big one as the bullet is actually flipping over inside the tissue, and then the bullet exits base first.) Once again, for fragmentation, speed matters as does bullet design. It was a happy accident that M855 Green Tip, allegedly built with a steel core for barriers, does this at high velocity. The jacket rips off and goes one way, the steel penetrator another, and the base of the bullet yet another. The data varies on the velocity needed for most FMJ bullets to do this, but a rough estimate is between 2400 and 2550 fps.

Rim dimension difference

Okay, so why the nerd out on ballistics? Because this is where it starts to matter. If we are talking about just a 5-inch pistol barrel, the 5.7x28mm round pushes a 40-grain projectile at around 1750 fps. Impressive, but below the thresholds mentioned for either wound theory as it relates to rifles. Does that mean 5.7 isn’t good enough in a handgun? Not exactly. There is one real-world example of the lethality of 5.7x28mm from a handgun, though I hate to give any credit to my enemy. When Nidal Hassan shot up Fort Hood, he was using an FNH 5.7. And while he was shooting unarmed Soldiers inside a building trying to do some BS paperwork, we also cannot ignore the statistics. 13 Soldiers were killed outright, and another 30 wounded. Considering 82% of those shot by handguns in the US survive normally, those figures matter.

30 round AR mag top, 40 round 5.7 bottom

Then we get to the rifle part of 5.7x28mm. While it was introduced in a pistol at the same time, 5.7 was always intended by FNH to fit in a submachine gun. Therefore, the caliber finds its ideal velocity in a 10.5-inch barrel such as the original P90. While our test model was a 16.1-inch barrel, CMMG does make both 10.5-inch uppers, and complete 5.7x28mm AR-style “pistols”. And in this platform, things start to change rapidly.

CMMG 5.7 mag is same footprint as 556/300AAC

From a 10.5 barrel, 5.7 can achieve some absolutely staggering velocities. Round dependent, 2350 fps is fairly common, and some newer premium designs make it all the way to 2800. Which, if you know anything about short barrel 5.56, should immediately have you scratching your head. Why?

Because that very nearly matches what 5.56 will do. It is well documented that 5.56 starts losing velocity as barrel length is shortened from 20 inches. 223/5.56 was made for 20-inch barrels, and it starts falling fast as you chop that off. With the proliferation of AR pistols in 8 to 11.5-inch barrel lengths, with 10.5 being the most common, this should cause a serious rethink. It turns out, 5.7x28mm will very nearly match 5.56 if you are packing a shorty.

3 rounds, 55 grain 556

Which opens up a lot of trains of thought. First of all, since it was designed for the barrel length, 5.7×28 doesn’t create the dragon’s breath fireball of shorty 5.56. 5.7 has less recoil, as it is a lower pressure round. I can tell you from shooting it in the CMMG upper, it recoils like a rimfire. And oh Lord, the difference in weight of ammunition. Some of this is in the projectile, to be sure. 55 grain 5.56 vs 40 grain 5.7. But still, the 5.7×28 weighs roughly half as much per loaded round of 5.56×45. It isn’t unreasonable to say you could carry twice as many bangs per pound by switching to 5.7x28mm. And be able to share ammunition with your handgun, which is basically a logistics dream come true. And did I mention the normal mag size for 5.7x28mm in an AR holds 40 rounds? Plus 20 in your handgun, that is a lot of bang.

3 rounds, 40 grain 5.7

These new guns, in tandem, have the capacity to shape the future. Especially as we see the price of 5.7x28mm drop as its popularity goes up. (We of the Cult of the 10mm have been blessed with this over the last few years as well.) At least if the ammo market ever recovers. It has been impressive enough to make me re-evaluate the 5.7, and I hope it does you too. I have a feeling the little cartridge that could is just getting started.

Recoil is so light it may as well be a 22LR

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About the author: Clay Martin is a former Marine and Green Beret, retiring out of 3rd Special Forces Group. He is a multi-decade and -service sniper, as well as 3-Gun competitor and Master ranked shooter in USPSA Production. In addition to writing about guns, he is the author of “Last Son of The War God,” a novel about shooting people that deserve it. You can also follow him on twitter, @offthe_res or his website, Off-The-Reservation.com

{ 25 comments… add one }
  • Higherview February 13, 2021, 8:12 pm

    I always find Clay’s insight interesting. This may be an idea who’s time may come – someday. But in a long term survival or SHTF scenario, the ability to restock at sometime should be a consideration as well as barter. Even during this time of shortage I come across 5.56 and 7.62×39 quite often. Just a quick look on Ammoseek shows the 5.7×28 is available at over $2.50 each (plus shipping) at the bottom end. 5.56 is going for .83+ cents per round (plus shipping) and 7.62×39 at .38 cents per round, and we know these are current prices way up from a few months ago. Even .308 can be had for around .80 cents for the Russian stuff. Trying to replenish these, or use them for barter in a SHTF scenario will give a person a lot more flexibility and availability. You might be able to carry more 5.7×28 and you’ll probably have a lot less weight in your wallet to drag you down. Someday it might be a reasonable scenario, and perhaps in a sort term survival situation it might be now. But once one is in a survival situation, how can you know it will be short term?

  • JohnL February 12, 2021, 6:22 pm

    Price vs 22 mag? performance (civilian) vs 22 mag? The next question is when you say survival in what condition and against whom? Are we talking post apocalyptic, behind enemy lines. BLM or on a hike? Personally I think the Israelis have it right. suppressed 10/22 ruger, lol!

  • Earl February 12, 2021, 3:04 pm

    Thank you for the article and demonstration pertaining to the 5.7 upper conversion. Did you have to make any modifications to the lower, or was it basically “plug and play” with the appropriate magazine for 5.7?

  • Geo Ling February 9, 2021, 9:53 am

    Clay, I have enjoyed reading your articles for a long time. And…I really appreciate your service to our Liberty!

    I’m not trying to be an ass but as we all know now days “words matter” 🤦‍♂️

    Now, since you hit this misuse of the term theory square on the head…

    “Now I say theory…”

    A theory in science is an explanation of a process that is “known”, is scientifically settled, it’s been figured out already.

    The proper term for a process that is not figured out but has a proposed explanation or several concepts that attempt to explain how the process works, is “hypothesis”.

    So, in context, we should read “…terminal ballistics hypothesis”. “Now I say hypothesis…”

    Now on with the great discussion of the 5.7.

    • Big Al 45 February 10, 2021, 10:01 am

      You need to reread the definition of ‘Theory”.

  • Leigh February 8, 2021, 5:20 pm

    Ammo was hard to find and expensive at the best of times. Maybe if more companies made it.
    Hornady…are you listening?

  • Norm Fishler February 8, 2021, 12:19 pm

    A friend recently bought a Ruger 5.7 and was thrown into catatonic arrest when he discovered how difficult it was to find 5.7 ammo. There was a time when I was keen on picking up an FN 5.7 but I have since cooled my jets concerning such. Ballistically, there is not such a wide gap between the 5.7 and the .22 WRM that I would put myself through such distress.

  • steve hammill February 8, 2021, 11:34 am

    TISSUE DAMAGE in deer:

    .270 velocity bloodshot – 10-12 inches in all directions around the bullet hole. Bloodshot meat must be handled separately from the rest of the deer.

    .45-70 – very little bloodshot, maybe 3 inches unless a bone is hit. The old-timers say you eat everything but the hole.

    I’ve butchered deer so badly bloodshot by bullet velocity that the shock of the velocity alone was probably enough to kill the animal.

    • Frank February 9, 2021, 9:23 am

      KUDOS on the velocity comments. I don’t know how anyone who has cleaned/examined big game animals taken with traditional high velocity cartridges, could question the absolute increase in lethality caused by cavitation (temporary wound cavity, hydrostatic effect… whatever term you prefer). I’ve taken whitetail deer with .22 LR,. 30-30, .30-06, .280, 7mm RM, .35 Whelen, and .54 patched round-ball. I’ve seen huge sections of the lung cavity turned to jelly by the high velocity rounds. I’ve also seen numerous exit wounds I could put my fist in. I’m neither a Ph. D., nor an MD., but I can conclusively state, VELOCITY MATTERS, and significantly increases the lethality of any round.

      • Big Al 45 February 10, 2021, 10:08 am

        Sorry, but there is no REAL evidence of your claim, and plenty off ‘Professional’ hunters and Guides have and do counter your claim.
        And when one considers the taking of so many Elephants ( and many other game species) by W.D.M. Bell with a 7 x 57 using solids, your claim falls on it’s face.
        Your further claim of “I can conclusively state” in the matter is arrogant at best.
        Peter Capstick wrote of this in “Death in the Silent Places”, and discusses several other P.H.’s sharing that opinion.

        • Frank February 11, 2021, 11:12 pm

          With regard to my apparent “arrogance”, my rather extensive law enforcement training, including research conducted by the FBI, reinforces my take on the matter. Nowhere in my comments did I state that velocity was the “only way” to effect a kill. If you would have paid attention, you would have read that I’ve taken big game with a .22 LR, a .30-30 Win. and .44 Rem. Mag… none of which are considered “high velocity” rounds vy today’s standards.

          Perhaps you are one who subscribes to the theory of “knock down power”, which was completely debunked by FBI research. When dealing with a deadly force encounter, the quickest way to incapacitate someone (absent a brain or spinal cord shot) is to create as large of a wound channel as possible. If you lack observational experience in game animals body-shot with high velocity cartridges, perhaps you can talk to a coroner or Armed Services surgeon about the effect high velocity rounds have on a human torso.

          You, sir can shoot whatever floats your boat. You can hurl large rocks with super-slow velocities at your chosen quarry. You will never however, be able to disprove the simple physics of all other things being equal, a higher velocity projectile creates a larger wound channel.

          BTW, Karamojo Bell made brain shots with his mauser. Capstick did the same thing with his .470 Nitro Express when dealing with elephants.

    • Baldbigears February 9, 2021, 1:41 pm

      If deer size game is headshot with a .22 mag then “Bloodshot” is not much of a problem. You can eat the whole deer. I know 22 WMR is not a legal hunting caliber in some areas but it drops game like a rock if properly applied to the cranium. You don’t need a cannon for hunting if you can shoot.

  • Eric Holder February 8, 2021, 11:29 am

    Compatibility of long gun and pistol magazines is a priority to many when trying to go down this road. I know of someone who had the FN pistol and bought the AR Banshee CMMG 5.7 The rifle was “not so great” and was sold in a few months. The 22TCM I think WOULD be a better choice but for the limited availability of different manufactured ammo. The OAL is better (shorter) than the 5.7 Although there are some Glock conversions for it, they require the use of the 22TCM 9R round. (dumb) they should have just made a conversion for the larger Glock 10mm or 45 pistols that would have worked perfectly with the standard 22TCM not the 9R variant. IMO the best firearm for this round currently would be the PS90. 16 inch barrel and 50 round magazine standard, very compact. Good article now back to packaging machine guns for undocumented persons and cartels.

  • Wes February 8, 2021, 11:14 am

    Positive and a negative-

    I’ve dropped a whitetail deer with one shot from the ps90.

    Negative. When competing and shooting steel plates the small 27 grain round won’t push over some steel plates like a round with more lead. But the fiveSeven pistol is so easy to shoot that I was able to triple tap to push over the steel plate.

    I can make solid 25 yard head shots and 50 yard body shots with the pistol. My wife prefers to shot the FiveSeven over my 9mm glock or mp2.0.

  • Cernunnos February 8, 2021, 9:37 am

    Look at all the BS in these comments. Most amusing. The SS190 is in fact it was designed to yaw well at pistol or SBR velocities, VS the SS109 which is as stated above a flying ice-pick. On Availability, I can still get 5.7 ammo today, $2/round. Hard to find 5.56 or 9mm at all, and if you do it is well over 1$ / round, and frequently $2/round. There goes that idea LOL. Nidal Hassan was taking center-of-mass shots on the majority of his victims, and head-shots only when close according to survivors. But as far as head shot potential, after running about 600 students in our defensive pistol training classes in 2019 where we had all of them try the FN Five-seveN, 98.2% increased their head-shot successes by at least 50%, and 100% had some increase. So the fact the ammo allows a greater potential for a head shot should not be viewed as a negative IMO.

    The velocities he used are off the shelf Fed American Eagle 40gr, or FN 40gr blue tip. Move up to real ammo like Elite Ammunition S4M, you get about 2600 FPS from the pistol, and 3100 FPS from the 10.5″ carbine. Plus Speer now makes Gold Dot for the 5.7x28mm. My only beef – and I sell a lot of guns in my shop – is the return rate on the Ruger 57s. Lots of magazine issues, lots of FTF and FTE – all in all if I carry the 5.7 round, it is in my tested and reliable FN Five-seveN MKII. The CMMGs are fantastic in my 10.5″ SBR and would be in the AR pistol too.

    Nice article – keep up the great work! For those wondering – availability of ammo is not a consideration for me – I have at least 15k rounds in every caliber I own (which I have pared down over the past 5 years to 9) and there is just no way I would run out of ammo in a WROL situation for over a decade. By then good luck finding ANY caliber unless you roll your own – and as we are seeing now – only if you have been stockpiling components, primers, powders, and projectiles for years. It is something that needs to be planned for and acquired over a number of years. In the current state of politics and insanity – you may not be getting much more of whatever you shoot for quite a while more from now. But let us hope not.

  • Phillip DeWitt February 8, 2021, 9:34 am

    From reading the 5.7×28 was designed for the military to defeat Chinese body armor as a sidearm/sub gun caliber.

  • Joe February 8, 2021, 9:27 am

    The 5.7 out of an AR pistol does perk my interst the cost of the P90 and ammo was always a big downer. This is like the modern version of having a 357mag hand gun and lever action. Always love your articles and vid keep up the good work!

  • Donald February 8, 2021, 9:21 am

    Another interesting article with lots of good information to ponder. That’s why I love reading Clay Martin’s reviews. I can’t afford to re-tool, as they say, no matter what the cost. I have too much invested in my current setup. My setup works for me. But… The information lends itself to new choices, and new debates. That’s a good thing for everyone. Research, research, research. Gain as much knowledge as you can from reliable sources. Then make your decision from all of that and gain as much experience as possible from that decision.
    Thanks Clay, for another enjoyable article.
    @BG Ferguson… Regarding your concern as to what’s behind the target being a safety issue… After putting the photos in some computer software and using the angle of the barrel, and judging from the angle at the top of the rise, the path of the bullet will strike the ground well before the rise at the top of the hill. Plus… We cannot see beyond the right side of the photos to what’s actually directly behind the target. Judging by Clay’s background. There could be an M1 Abrams MBT set up for his next review. Safety is very important, so, along with pointing that out, there was much more to his article worth commenting on as well.

  • RSConsulting February 8, 2021, 8:41 am

    Sigh – 5.7 pimping…

    I still have my FN57 – purchased right after the Fort Hood incident. Purchased mainly for capacity, and it’s obvious demonstrated ability to maim & kill. Probably have about 1,000 rounds of original FN boxed ammo for it also – even some of the LEO Only SS190 stuff.

    That being said – survival requires you to be able to RE-ARM, usually from the ammo of “vanquished foes”, and we’re not going to find very many of those, SHTF, out in the Mad Max world we are rapidly creating.

    I was drooling over the Ruger 5.7 – top of my list – until a friend got one, and I found it didn’t really fit my paw well. Not that mind carrying a full sized pistol (current carry is a Kimber Pro Carry II in GODS CALIBER – .45 – when you KNOW HOW TO SHOOT – you don’t need 21 rounds). OFF the list.

    The CMMG upper is interesting though. Don’t know that I’d get one in 5.7. I’m really liking the Sig piston uppers with integral bolt/recoil systems. NO BUFFER TUBE REQUIRED – which makes for a much more compact weapon system with a folding/collapsible that you can fire closed.

    Then again – I also have a Tavor SAR & T-7 – loving bullpups lately for CQB/urban/house clearing.

    Good ballistics writeup though. But again – as others mentioned – cost/availability, especially in “survival mode”, don’t really make this a logical choice for load-outs. 5.56 & 9mm are going to be the rounds “most available” in the field, and also good for barter should things continue to go sideways. Wish I had more 5.56 – but I have plenty of 7.62×39 & 51, 9mm & .45.

    Always interested when I see a 5.7 article. No doubt one of the more interesting of the “weird calibers”. Not enough to make me get more of them though.


  • DavidInCO February 8, 2021, 8:27 am

    At CMMG, the AR conversion seems to be on par with a high quality AR upper. However, the ammo… At $2/rnd, I’ll pass for now. Maybe things will return to rationality sometime soon.

  • Bad Penguin February 8, 2021, 7:50 am

    Nidal Hassan was shooting those FT Hood soldiers and was trying to take head shots on all of them to ensure the hits were fatal.

    Also the SS109 Bullet was designed to not yawl so as to penetrate Soviet body armor. The result was the 109 was a flying ice pick that tended to wound more that kill as compared to the older ammo. Th newer army ammo was designed for penetration a yawl when hitting flesh.

    BTW at what range does the 5.7 ammo drop below the speed needed for the hydrostatic effect and at what range does the bullet fall below the speed needed to fragment when fired from a rifle? Most places in the eastern US a 100 meter shot would be a long one but could expect to kill or wound the target.

  • Joe H February 8, 2021, 7:38 am

    Although concurrent with the authors data points, the matter of 5.7 price has always been an issue long before the ammo panic. I have owned both FN platforms yet decided to sell due to ammo cost reasoning. A mistake or not, second guessing that decision can be in the cards however if one is going to pic a survival cartridge or a catch all, the 5.7 IMHO is not my choice do to the uncommonality.. I don’t downplay the extreme fun and appreciation for the 5.7 but it all rolls into availability and cost for most… great article to get the juices flowing….

  • BG Ferguson February 8, 2021, 7:16 am

    The photos of your shooting range show the slight ridge in the background and the land falling away beyond your vision. Shouldn’t you have a backstop that rises up and not falling away? How do you know if there is or isn’t a person, vehicle or someone’s dog just beyond the rise and in the path of your bullets?

  • Leo February 8, 2021, 6:50 am

    Great caliber but did you saw it in stores? Or even if in stores what was last price on it?

  • stan92166 February 8, 2021, 6:35 am

    I have been pondering this exact same thing. Is the cost of two new plat forms worth it?

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