Future Firearms Ammunition Technology 003: Sabots – Performance-Enhancing Shoes for Your Bullets

Sabot rounds, left to right: XM645 SPIW flechette with compressed disintegrating puller sabot, XM645 SPIW flechette with glass polyester disintegrating puller sabot, 5.77/4.32 Frankford with polymer cup pusher sabot, 5.56x45mm AAI ACR flechette with petal-type puller sabot. Far right is a pulled SPIW sabot and flechette.

Sabot rounds, left to right: XM645 SPIW flechette with compressed disintegrating puller sabot, XM645 SPIW flechette with glass polyester disintegrating puller sabot, 5.77/4.32 Frankford with polymer cup pusher sabot, 5.56x45mm AAI ACR flechette with petal-type puller sabot. Far right is a pulled SPIW sabot and flechette.

One of the problems of small arms ammunition is that of swept volume. That is, the most ballistically efficient projectiles are the longest and thinnest ones, which cut through the air more easily than squatter, fatter projectiles. Yet, the best projectiles from a propulsion perspective are the widest ones, as they have the most area at their base for the expanding gases to push on, making them more efficient, especially from shorter barrels.

In a conventional gun, these two dimensions cause a compromise: A wider projectile increases the efficiency of the gun, reduces barrel heating and wear, and reduces velocity loss from shorter barrels, but it doesn’t fly as far as a thinner, sleeker projectile. But, there is a solution: Sabots. From the French word for “shoe”, a sabot – or more correctly a discarding sabot – is a piece of material that bridges the gap between the thin, sleek projectile, and the wide, efficient bore of the gun. Sabots guide the bullet down the barrel efficiently, but are discarded after the projectile exits the muzzle of the weapon, and do not carry on to the target.

Sabots come in several forms, which can be simplified into two dimensions:

  • Pusher, or puller

and

  • Cup-type, (for lack of a better term) splint-type, or disintegrating-type

The first point describes how the sabot engages with the projectile, whether it pushes from the back of the projectile, or pulls from the middle or front. The second describes how the sabot disengages from the projectile. Does it fall away from behind, fall off from the sides, or disintegrate entirely? In theory, a sabot could be made that embodied any one of the six combinations of the five types above, but generally only cup pusher, splint pullers, and disintegrating pullers are used.

Sabot_separating

An APFSDS tank round during sabot separation. The splint-puller type sabot falls off from the sides of the long, thin projectile, which carries on to the target.

 

Sabots are closely related to another topic we’ll be covering later, which is the drag-stabilized arrow-like flechette, but they have other applications, too. With conventional bullets, sabots allow for a smaller, longer projectile than could be otherwise practically rifling-stabilized, as the size of the rifling needed to spin such a projectile is larger and easier to make thanks to the wider bore. Also, a chambering could be made such that it was compatible with both saboted small-caliber bullets, and bore-riding large caliber subsonic projectiles, potentially giving future ammunition both the good trajectory of small-caliber high-velocity rounds like 5.56mm and the versatility of rounds like the .300 AAC Blackout. For high-velocity ammunition intended to be fired from very short barrels, sabots are potentially a huge boon, dramatically increasing the efficiency and therefore velocity of such ammunition. Finally, very high velocities at the limit of current propellants – those over 4,500 ft/s – are virtually only achievable with sabots.

However, this concept in the context of military small arms has been experimented with for well over the past 50 years, and hasn’t yet reached production status, which indicates that serious downsides exist. Typically, sabots significantly reduce the accuracy of the gun, as clean, repeatable separation of a small-caliber sabot from the projectile is very difficult to achieve. As a result, the dimensional tolerances of the sabot and projectile both need to be kept very small, which increases the cost of ammunition.

Even so, the sabot-driven long rod penetrator is the standard armor piercing ammunition of today’s armored fighting vehicles, and saboted projectiles have been successfully used with shotguns in hunting applications for years, so the concept is workable to some degree. Will it ever reach prime time for small arms?



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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  • Tim Pearce

    There have been sabot rounds on the civilian market, as well, though for a different reason. I don’t know of any other round beyond the Remington Accelerator line, wherein you would be able to fire .224″ projectiles out of your .30-06, for example.

    I don’t know, but I’d assume they were discontinued due to a mixture of unreliable release from the sabot causing accuracy issues and the shooting community’s general dislike of new ideas. I.E. they probably sold poorly, to only a few people, and then those few people saw no reason to continue buying them.

    • TechnoTriticale

      It was suggested in an earlier thread, where the .22RA came up, that the major problem with accuracy wasn’t necessarily sabot separation, but that your pre-existing rifling twist was optimized for a much slower .30 caliber projectile.

      A new intermediate military round based on a sabot would likely require a weapon optimized for that ammunition.

    • Kivaari

      They cost too much. People wanted a varmint rifle in their .30-06, but the ammo was both inaccurate and too costly to practice with. What I found with my customers is they liked the concept, but would just a s soon buy a new rifle to do the job with.

  • Major Tom

    I’ve heard one of the biggest downsides to sabot ammunition for small arms is it passes below the lower limit for practical lethality. In other words, speedy shot goes in you and speedy shot goes out the other side with only a very thin hole along the way. Aka very poor wounding characteristics.

    That and like the SPIW program with duplex flechette loads proved, accuracy is compromised. Additionally the flechettes would deflect off the lightest of obstructions, stuff even the notoriously deflectable M193 5.56mm ammunition would not deflect off of.

    Sabot ammunition is useful in anti-vehicle use because you have to penetrate armor and/or frame to get at the vulnerable bits inside such as crew, fuel and ammo.

    • ostiariusalpha

      Tests with ballistic gelatin showed that flechettes were just as reliable and potent at wounding as M193, it really was the degradation in precision that killed the SPIW program.

      • Kivaari

        I received a letter from Dr. Fackelr when this was a hot debate between Picatinny Arsenal and the Wound ballistics Lab In SF. Fackler found the wounding by the proposed sabot rounds to be less than ideal. He simply hated the idea and thought his fellow soldiers at the other lab were totally wrong. I would go along with Fackler even though I haven’t read much more on the subject. Ice pick wounds don’t do much unless they cut major nerves or hit bone.

        • ostiariusalpha

          The flechettes very definitely tumbled and buckled reliably in the gelatin blocks, Fackler’s objections did not change the simple physics. His observations of the wounding capacity of artillery flechettes was pretty spot on, but his projections from those results were unfounded.

    • CommonSense23

      You got a source for the fact that M193 is “notoriously deflectable”?

    • You are conflating sabots with SPIW-sized flechettes; these are two different things. I discuss flechettes specifically in a later post.

      Although flechette ammunition is virtually obligated to use a sabot, sabots can be used for many different things.

  • Patriot Gunner

    I wonder if they would work with a suppressor….

    • roguetechie

      Yeah you can make them work with an integral suppressor quite easily since they depend on ported barrels and I suspect with certain suppressor designs you could probably get away with it. Especially some sort of reflex suppressor with barrel ports.

      • Patriot Gunner

        Ahh good point..thanks for the clarification. I was thinking if the suppressor is on the end of the muzzle (as is traditionally) then sabot separation would be a problem.

        • roguetechie

          Yeah, especially if the very high pressure and bouncing shockwaves interact strangely with the sabot and cause asymmetric separations and the mother of all baffle strikes!

          And you thought that running a quad rail that goes over your muzzle brake could result in some Elmer Fudd gun splitting action…

  • roguetechie

    6.5 cbj seems to have solved many of the problems with smaller caliber saboted rounds, where it failed was in going so small that it was only launching 4mm tungsten slivers.

    That technology scaled up to a 5.56 case with no shoulder or altered shoulder and neck can and should be pursued. CBJTECH AB is looking to do exactly this as well as something similar with a 7.62×51 round.

    So far in the comments I see mostly misunderstanding and lots of talk about very small caliber flechette ammunition, not discussion about actually using Sabots with more traditional bullet design.

    Honestly I suspect that half the reason we aren’t seeing more movement in this type of research is because so many people come into the conversation only wanting to repeat what they’ve heard or read about unrelated concepts. Thus neglecting to actually take the time to understand what is actually being discussed or proposed.

    Really with the direction and path firearms are currently on, and the physical Characteristics needed and wanted in modern firearms and ammunition the sabot is about the only way we have left to gain anything more than trivial amounts of performance and multipurpose usability.

    That is, of course, outside some major paradigm shift in our understanding of the physics of firearms operation and construction, ballistics, new propellants, or sudden discovery of much cheaper and easier to manufacture superalloys or other materials drop in our laps.

  • gunsandrockets

    Sabots too tricky for small arms ammo? Go back to the future with squeezebore rifles.

  • Edeco

    Practical sabots are a major thing on my wishlist. I really like long barrels relative to the propellant charge. I don’t enjoy inefficient guns, to me running a 5.56 down a 14.5 inch barrel or a 7mm magnum down a 20 inch barrel would be like putting a 350 in one of those Lotus Seven chassii; neat trick, but destroys the elegance. More area for the gas to push on for a given projectile would be awesome.

  • DanGoodShot

    I’ve played with them using .223 out of a 300blk and .308. I got ridiculously crazy velocity but crap for accuracy. I found them good to 75 yards. Even that was stretching it a bit. But damn they got there quick! Oh and you can’t use a muzzle brake or comp with em. Flash hider is ok. Not a bird cage though. Three prong type is g2g.

    • John Yossarian

      Well there’s a recommendation for saboted ammunition right there – An end to the proliferation of muzzle brakes on 5.56 to 7.62 NATO-sized rifles!

  • noob

    I wonder, in a hostage rescue scenario, would a police officer shooting a sabo rounds out of a submachine gun find that some of the discarded sabots impact the hostages with tragic effects even though the actual projectile flew true and straight at the hostage taker?

    or, flipping it around, could the sabots themselves be part of the wounding mechanism at close range – so the carbine performs like a flat shooting rifle at long range, but the user knows that it will pattern like a shotgun with the bullet hole in the middle and sabot holes surrounding the bullet hole at random?

    I know that the Surface Danger Zone templates for tank sized sabot ammunition are very wide. you probably aren’t safe unless you are far enough away that aerodynamic drag has caused the sabot to hit the deck.

  • George

    Why “splint type”; it’s uniformly described as spindle in tank gun ballistics I have read?

    I have deep faith in the future of sabot rounds in small arms, but not this or next years. Shrug. None of the issues are ones scaling laws suggest should be inherently different at 6mm vs 25 or 40 or 120mm. That does not translate into rounds available for test now.

    • In small arms, they don’t really look like spindles, but I guess you could call it that.