Not All Penetration Data Is Created Equal

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The subject of armor penetration previously was largely confined to the realm of big bore rifles or cannons intended to tackle tanks and other kinds of armored vehicles, but as the popularity of steel and composite body armor increases, it has become more and more relevant to the subject of small arms. It may be tempting to pull contextless data from different sources, and present them as being comparable, but in most cases this is a mistake. Unfortunately, quoting armor penetration numbers from two different countries or organizations is not a good way to compare the capabilities of rounds against one another, as I will explain.

For this article, we’ll be using figures for the US .50 BMG M8 steel cored armor piercing incendiary round, and the Russian 14.5x114mm AT/HMG BS tungsten cored armor piercing incendiary round. These are two very dissimilar types of ammunition, and the figures used in this post are, as we’ll see, only examples and should not be used for reference.

There are several reasons why penetration data is best compared within a single source, or only between standardized sources (for example two separate tests conducted by the same organization). First and simplest, the armor quality used by different organizations and countries is not necessarily the same, even if the plates are each listed as “RHA” (rolled homogeneous armor, a rough testing standard). Second, the methodology used by the testers makes a huge difference. Let’s suppose that we have numbers found in a Soviet source for the 14.5mm BS round, and numbers found in an American source for the .50 caliber M8 API, and state them like so:

14.5mm BS penetrated 30mm at 100m distance, and 25mm at 500m.

.50 caliber M8 penetrated 25mm at 100m distance, and 18mm at 500m.

Note that in this example I used round numbers for the 14.5mm. Round numbers may be indicative of statements like “the round will penetrate these plates at this range”, versus a statement of “when shot at a very thick plate the round penetrated this deeply into it”, but unfortunately when stripped of necessary context, it’s impossible to tell for sure. These are very different statements made from different testing methods that will give you very different results even with the same round. Consider, for example, that testers could fire a 14.5mm round at a 1mm plate, and it would indeed penetrate it. If it was then stated as “14.5mm will penetrate 1mm of armor at X distance”, that’s technically true but that is clearly not the maximum thickness the round will penetrate. This is just one example of how testing methods may differ, there are many, many more, including the plates being set up at different angles to the shot, the plates being held or supported in different ways, etc.

Third, penetration and perforation may be an additional source of confusion; penetration is where the projectile breaks through the armor, while perforation is where the projectile passes completely through. To make matters worse, sometimes the word “penetration” is used to mean either penetration or perforation!  Further, not all shots are the same, even in controlled conditions, and therefore many testing organizations have standards as to how often a shot must penetrate or perforate a plate. Suppose that 14.5mm perforates a 30mm plate 100% of the time at 100m, but .50 penetrates a 25mm plate 50% of the time at 100m. Just saying “14.5mm penetrates (general term) a 30mm plate at 100, and .50 penetrates a 25mm plate at 100m” makes them sound similar in capability, when in fact this is very much not the case; the 14.5mm in this example is much more powerful and capable.

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A 17 pdr (76 mm, or 3″) projectile has penetrated, but not perforated, this section of 6″ test plate. Due to spalling of the metal, this would still likely have posed a great threat to the crew of a vehicle. Image source: reddit.com

 

Can we tell whether the comparison in the quote box above is a good or a poor one? Well, for a start, the 14.5mm BS round is clearly a much larger and more powerful cartridge than .50 BMG M8, with more sectional density and almost 400 ft/s more muzzle velocity, but that does not necessarily mean that it will have superior penetration characteristics. However, the former round uses a tungsten core, whereas the core for the .50 M8 API is steel. Tungsten is a much harder, denser material used in projectiles almost exclusively for its excellent armor penetration capabilities, far above that of steel penetrators. This plus the larger size and higher velocity of the 14.5mm BS strongly suggests it should have greatly superior armor penetration characteristics vs. the .50 M8. We can help verify that assumption with some historical context: During WWII, the similar but less capable tungsten-cored BS-41 API was still effective at about 100 meters against the vulnerable 40mm thick unsloped side hull armor of Panther tanks. This was in fact such a problem for the Germans that they introduced side skirts on their tanks to counter it!

The only way to truly tell how two rounds compare with one another for penetration is to do it the hard way, by testing them repeatedly against homologous sections of armor at different ranges. There are available some test results that give a good picture of how different historical cannons performed versus one another, but unfortunately the same kind of rigorous testing is not really available for small arms ammunition. As armor plates become cheaper and more available, however, this may well change.

 

Thanks to marathag for his contribution to this article.



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 can be reached via email at nathaniel.f@staff.thefirearmblog.com.


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  • MPWS

    Well funded article, but touch carried away with emphasis on small arms ammo. those skirts on German tanks were for protection against cumulative/shaped rounds, not puny 14.5.

    • 2.3.10 SCHUERZEN – PROTECTIVE SKIRTS

      Starting in April 1943, Schuerzen (protective skirts made from soft steel) were mounted to prevent penetration of the 40 mm thick lower hull side by rounds fired at close range from Russian anti-tank rifles. The Schuerzen were tested and proven to be effective against direct hits from 75 mm high-explosive shells as well as anti-tank rifles. The invention of Schuerzen saved the Panther I. If the Panther I hadn’t been able to cope with anti-tank rifles, production would have been converted to the Panther II. The Schuerzen were not intended to defeat and were not initially tested against hollow charge rounds.

      Jentz, Doyle, “Germany’s Panther Tank: The Quest for Combat Supremacy” page 35

      • BillC

        Daaangg, MPWS got told. I mean, “corrected”.

        • iksnilol

          The Nathaniel (of the surname that starteth with F) giveth, and the Nathaniel taketh.

          So it sayeth in the holy comment scripture of the blog only known as TFB.

        • Yourguy

          Owned! That’ll teach him until next time that is….

      • mosinman

        this also goes for the Shurtzen on the Panzer 3 and 4 tanks

      • Zebra Dun

        The rounds would waste their penetration on the skirt and be less effective when they did go on to strike to tank.
        Same with HEAT which has it’s molten copper stream disrupted by such stand off.
        Funny how Chain Link fence can do the same for HEAT.

        • Chain link/bedframe/grate armor is designed to prevent HEAT from fusing, primarily. Some kinds of heat are capable of defeating standoff, anyway.

          The reason that skirts were effective against AT rifles was that the rounds would penetrate the skirt and go through at a slight angle. This would either cause them to hit heavier armor or to hit the flat side armor at a substantial angle, preventing a penetration.

          • Zebra Dun

            A good thing to know for sure.
            Of course HEPT is another factor to figure in LOL

  • Stuart Hunter Keough

    That’s just about the coolest hunk of metal I’ve ever seen.

    • Guest

      Make that a centerpiece on a coffee table! I need one!

      • Giolli Joker

        I guess you’d need something stronger than the average IKEA stuff to hold it… considering the diameter of the bullet is 3″, the full piece is probably pretty hefty. 🙂

        • marathag

          Cubic foot of steel is around 500 pounds, so a 6″ x 12″ x12″ paperweight would be around 250 pounds

          • Giolli Joker

            Yep, my metric guesstimate was in in the 110kg range, so pretty close.

    • marathag

      While my other comment with links waiting to be approved, google on Shinano plate penetration for a real cool chunk of metal

      • KestrelBike

        hopefully a TFB mod sees and approves it, sometimes I think they don’t pay attention and good comments disappear into the bermuda triangle.

        I’d love a better sense of scale from the OP’s photos, the shell looks much bigger than 3″ diameter.

        • 3rdweal

          It’s an armor piercing shell fired by a 17 pounder anti-tank gun, 3 inch caliber.

      • nadnerbus

        I thought of the exact same thing when I saw that picture as well. I’ll just steal a pic of it from google image search.

        I guess the story behind it was that it was from the third Yamato class ship’s front turret armor. That ship was later converted to a carrier but sunk prior to commissioning.

        They took the armor after the war to test against the 16inch AP round. Pretty crazy amount of power there.

        Keep in mind that it was a more or les straight on shot, and I don’t know the range but I’m sure it was relatively close. A plunging shot from many miles, as would have been the case in combat, probably would have looked a lot different.

  • UKShuggy

    This is precisely why NATO has STANAG 4569 and AEP-55!

  • Wolfgar

    The original Tiger Tank had in many ways better armor than the thicker armor of the King Tiger. Due to the lack of strategic metals, “mainly Chromium which made the armor more ductile”, available in Germany near the end of the war, the King Tiger’s armor was manufactured with inferior metals compared the original Tiger tank. The inferior armor used in the King Tiger was more vulnerable to spalling even though it was thicker. Another excellent observation and article Nathon.

    • marathag

      Too high a hardness can be worse than too low of a hardness, when ductility is too low, you get cracks.

      • Wolfgar

        Yes and the reason standards in penetration test need to be used as pointed out in Nathon’s article.

    • Jon

      The problem in German late armour in WWII was its lack of ductility due to the lack of nickel not chromium.
      By the way, the false thinking of huge German tank superiority over Soviet ones comes from a variety of reasons, as the way German counted tank loses (any panzer with so big damage it needed to be loaded in a train to give back to assembly factory didn’t count as a lose, but they counted as destroyed any knocked out Soviet tank, regardless if that tank could be repaired in the field with little effort or it was completelly destroyed), cheating about destroyed enemy tanks (once a Jadpanther informed 11 destroyed tanks in a tankless Soviet front) or the same reason explained in this article, for the Wehrmacht spalling counted as penetration, for the Soviet penetration was a sinonime of perforation.

      • Wolfgar

        I thought it was chromium but you are probably right about it being nickel. Yes the German tanks had a reputation way beyond reality. The original Tiger was a beautiful machine with power steering and abundant room. It also had reliability issues, hard to change over lapping wheels and design flaws. The Germans had excellent training and communications which proved superior to the Soviets at the begging of the war. Not so much at the end of the war not to mention over whelming odds against them. There has been much discussion about truths vs reality of German battlefield victories which seems to have merit. Thank’s for the correction.

        • Zebra Dun

          It’s main faults was constant breakdowns, it’s weight and the fact there were so few of them.
          Every tank an Infantryman saw during WW2 was a Tiger, yet there were way more Pz IV and STuGs than any Tigers.
          The records show the majority of tanks, Allied and Axis, k or M killed were knocked out by Anti Tank weapons on vehicles and hand held Infantry anti tank weapons.
          Mines did the next best in K and M kills.
          Actual gun K and M kills were very few.
          HEAT it seems was the penetrating weapon of choice that worked then.

      • Bronezhilet

        I’m sorry mate, but the Germans never used nickel in their armour.

        There are various metallurgic reports floating around. All of them show that the armour plates themselves contained only trace amounts of nickel, while the welds contained, on average, a few percent nickel.
        This was the case throughout the war, even when the Germans were still winning they never used nickel in their armour.

      • Zebra Dun

        Same in Vietnam, any helicopter no matter how destroyed was not considered lost if it was recovered from the crash site.
        Same as wounded troops, if a casualty lived long enough to fly out of RVN and they died on the way to Japan or in Japan they were not counted as lost in combat.
        The M-4 Sherman was a better tank in that most combat damage could be repaired in a close by Rear maintenance depot.
        The slant of the M-4 frontal plate is what gave it’s armor a theoretical better thickness than a Tiger’s.

  • GreatName

    just the tip, huh

    • Evan

      Just the tip works every time. You know, “spalling”.

    • Zebra Dun

      The first inch is the area you must hit and penetrate. ; ^D

  • The Wound Channel

    Neat!

  • Kelly Jackson

    99% of AR15 dot come still thinks Russian mild steel jacket ammo could pierce that slab.

    • iksnilol

      Not that hard if you shot through the hole in the middle (provided the projectile is removed). 😀

  • doyle hill

    This is also how to examine medical pharmaceutical/vaccine claims. Separate tests normally shouldn’t be held up side by side as comparisons. The tests should be done concurrently in the same environment under the same set of criteria.

  • Tassiebush

    I really enjoy these types of topics. I wonder how depleted uranium rounds compare to tungsten?

    • Too technical for me, especially since a lot of the data for modern APFSDS rounds is classified. I do know that the US uses DU for the latest designs of 120mm tank ammunition (such as M829A3) because it’s pyrophoric (sets stuff on fire) and self-sharpening.

      • Tassiebush

        It seems to be remarkably good for the purpose. I read somewhere (possibly here) that DU was used for shot in that quiet captive piston revolver round developed for tunnel rats in Vietnam.

  • DW

    Not All Penetration Is Equal
    ( ͡° ͜ʖ ͡°)

  • I actually found a different post with the same image where the OP had embellished the 6 inch plate into a section of Tiger hull (that’s why there’s a discussion about the Tiger elsewhere in the comments). Originally I repeated the error, but some of my buddies set me straight. 😉

  • There’s some good stuff there, people should go over and read it. To be honest, the images I used came after I wrote the article. Not much of a redditor, hahah.

  • Just load some premium gold rounds. – WOT

  • nova3930

    Good article going into the details of why standards matter

  • Jon

    Yes, you are right. I read it in a non metalurgy specialized WWII book. I researched and my information was wrong.

  • Wolfgar

    Great find Bronezhilet, right from the horses mouth. Not only were the Germans armor lacking the proper metals but their welded joints”electrodes” were lacking chromium replaced with available manganese. Improper armor quenching made the steel brittle. Now we know. And to think no insults were thrown around to acquire the proper information. 🙂

  • Zebra Dun

    Don’t forget slanted armor.
    A penetration on a set thickness of 90 degree plate may fail at a 45 degree slant.
    The incendiary of course means damage needs to be done after the round has entered the armors soft areas.
    Seems you can get optimum penetration but less than desired effect after penetration or you can get maybe penetration with maybe effect after, the trick is getting effect on target after getting effect on penetration.
    The dual purpose round is the key.
    ———-
    We got a hold of some old 30.06 Armor Piercing ammo back when I was a kid, old WW2 stuff my buddies Grand dad was an antique dealer and bought an estate that contained an old Mauser I believe converted to 30.06 and well over 100 (+/-) rds of AP and tracer.
    He was given this at the age of 14 fun was on the agenda!
    WW2 ammo we were told was preferred by the GI’s of that war.
    We shot everything we were allowed to shoot and found out many interesting truths.
    For instance shooting through vines/small limbs inadvertently in the woods at a target made the jackets separate from the steel penetrate and the steel would hit the target and sometimes the jacket would simply hang up in the vine/small tree limb, the steel sometimes key holed after this. Sometimes the entire bullet jacket and all wood drill a .30 caliber hole through what it hit and continue to penetrate the target.
    There was this old Corvair we shot at it from the rear, rds that hit the almost level hood bounced off into the glass where they entered.
    Car bodies were like shooting tissue, straight through.
    Engine blocks could be penetrated but no through and through. Similar with tranny’s, wheels and other hard steel items.
    Pine trees absorbed the entire round as did other trees over a certain diameter.
    Bags of dirt and sand collapsed after a few rounds.
    Rocks and cement as well as brick and cinder block were NOT cover.
    The most amazing thing for this 14 yr old was the fact that tracer rounds fired into a stand of trees made a zig zag pattern ricocheting off the trees!
    I said “Hey I never saw that happen in combat TV show!”
    There was also an old French Lebel that we tied to a tire and shot with a string with the old ammo that came with it, and it promptly exploded.
    Now days any 14 year old who did this would be sent to prison for years.