Isegoria

A rifle round’s effectiveness depends on its crack & splash, Emeric Daniau explains:

In the first report, the acoustic and visual signature of several rounds are compared, including the XM645 “flechette” round fired from the XM19, the 5.56 mm M193 fired from the M16, the 7.62 x 39 mm fired from the AK, the 7.62 x 51 mm fired from the M60, the .45 ACP fired from the M1A1 SMG and the .50 BMG fired from the M2 HMG.

Those results will serve to identify physical parameters that could be used to build a relative scale for suppression, accounting for both acoustic and visual stimuli.

Results from the second report will be used to correlate this relative scale to real life “threatening” distance.

[...]

Live fire test performed at a distance of 150 m revealed that:

• the mean dangerousness of both the XM19 and the M1A1 SMG were rated significantly lower than other weapons, the XM19 being rated significantly lower than the M1A1,
• subjects failed to discriminate the AK from the M60, and the AK from the M16 (“From Table 5-14 it can be seen that only the comparisons of the AK47 with the M60 (+0.16) and the AK47 with the M16 (+0.23) fail to reach the ICI of 0.38 necessary for the demonstration of a significant difference in the mean perceived dangerousness for the two weapons”), but the difference between the M16 and the M60 could be considered significant (a ICI of 0.39 was achieved between those two weapons).
• the .50 BMG scored the highest mean dangerousness value, but the result was not found “off scale” compared to other weapons,
• mean dangerousness decreased linearly with the miss distance (minimum miss distance considered was 2 m).

[...]

Again, live fire tests performed at a distance of 150 m revealed that:

• the M1A1 SMG in the visual signature mode received a higher mean suppression scale value than did the M16,
• the visual effect of the .50 BMG M2 HMG was so much “off the scale” compared to other weapons that it was not possible to find a statistically significant difference between the M1A1 SMG, the M16 AR and the M60 MG (the XM19 was not rated).

It was anticipated that the visual signature of impacting bullets would be related to kinetic energy (because cavity volume in soft soils is directly a function of the kinetic energy), but the rating of the M1A1 SMG over the M16 suggests that other mechanisms could be involved.

This unexpected observation could be linked to the ricochet characteristics of those very different bullets, a low velocity.

[...]

For the 7.62 mm, a miss distance around 6 m will produce 50% of suppression, compared to around 3 m for the 5.56 mm and the .45 ACP, and 24 m for the .50 BMG (a class of its own, and ~4 times the miss distance of the 7.62 mm).

Presented differently, at a (presumed) distance of 150 m a single 7.62 mm NATO (24 g cartridge) could be expected to supress 50% of a group located in a 113 m² area, compared with 28 m² for the .223 Remington (12 g cartridge) and 1,800 m² for the .50 BMG round (115 g cartridge).

So, if we divide the suppression area by the cartridge weight, we found that at a distance of 150 m, 1 kg of .223 Remington ammunition will provide a 50% suppression effect in a 2,350 m² area, 1 kg of 7.62 mm NATO ammo will cover 4,710 m² (twice as much for the same ammo load) and 1 kg of .50 BMG will cover 15,700 m².

The miss distance for achieving suppression 90% of the time is much shorter, around 0.7 m for the 7.62 mm NATO, less than 0.5 m for the 5.56 mm and the .45 ACP, and 5 m for the .50 BMG (again, a class of its own in the realm of kinetic energy small-arms).

Emeric Daniau summarizes the historical trends in individual weapons over the last century:

The rise and fall of the effective range of the individual weapon can be seen as a direct effect of the “competition” between infantry fire and artillery fire in producing battlefield casualties, and a compromise between the effective range and the practical rate of fire.

If in the 60 years before 1914, less than 10% of the battlefield casualties were produced by artillery fire, during (at least) the 60 years after 1914 artillery fire replaced long-range small-arms fire as the main casualty factor.

The need to continuously increase the volume of fire led to the reduction in the practical range of small-arms to less than 400 m, and allowed the rifleman to carry and fire more cartridges with his individual weapon.

During the same timescale, infantry fire changed from collective fire aimed at compact columns manoeuvring in the open, to individual fire aimed at a single fleeting target using the maximum concealment and cover.

Under these engagement conditions, the hit probability of infantry fire was found sufficient up to 100 yards, and very low at ranges longer than 300 yards.

In order to increase the efficiency of the infantryman’s individual fire at long range, the concept of “controlled pattern dispersion” (ideally, 5 shots in a diamond pattern) was first introduced but for proper execution needed to use a “low recoil” cartridge.

The adoption of the 5.56 mm in the M16A1 was seen as a first step in this direction, but battlefield experience revealed that the recoil of the 5.56 mm round was not low enough for achieving “controlled dispersion” at ranges higher than 50 m, and most western armies have recently come back to semiauto firing only. Further reduction of the recoil impulse (like the .17 SBR among other experimental diminutive cartridges) was not so successful due to the concomitant reduction of terminal effectiveness, the Russian 5.45 x 39 mm being probably the best balance of reduced recoil and useful lethality.

Up to now, it seems that the closest practical realisation of the concept of “controlled pattern dispersion” is the G11 “3 shot burst” free-recoil system (at 2200 rpm) and the AN-94 “accelerated double-tap” (2 shot burst at 1800 rpm), two systems that have not achieved wide acceptance due to the mechanical complexity involved and have yet to demonstrate tactical interest compared to semiauto firing.

During the ‘90s, medium-velocity grenades of limited diameter (20 mm – 35 mm) with “effective” ranges around 600 m, were seen as a way to compensate for the infantryman’s lack of accuracy at long range, but without a proper “all weather” Fire Control Module enabling a fast acquisition of the target (it is doubtful that any soldier will be willing to expose himself to enemy fire for more than ~2 seconds), the average miss distance of such medium-velocity grenades will remain much higher than their effective casualty radius and the improvement of the infantryman’s hit probability is open to question.

The current trend toward “medium velocity” 40 x 46 mm grenades is also open to question, because between 0 to 350 m (and particularly between 50 m and 150 m), medium velocity grenades will impact the ground at shallower angle than a low velocity round, increasing the fuse malfunction rate and also reducing the warhead effectiveness if the round actually detonates.

Anyway, shoulder launched grenades (low-velocity, medium velocity or rifle grenades) have a definitive place on the battlefield because they provide both additional capabilities (against defilade targets for example) and effective suppressive effects.

A few grenades exploding behind enemy lines is a known way to distract opponents firing at you, making them thinking that they are attacked on two sides, even with a miss distance between 20 m and 50 m. Of course, for this task there is no need for expensive programmable fuses and even more expensive FCM, a simple HE-FRAG or HEAT rifle grenade will do the job.

Additionally, with a simple 3-axis accelerometer and a GPS chipset (like those found in every smartphone) wired into the grenade-launcher, it’s probably easy to design a simple “indirect sight” that will show the grenadier the expected point of impact and CEP radius of its grenade on “Google Earth” (or  something similar), enabling this high trajectory weapon to be used without exposing the shooter to returning fire.

As a side note, readers should be interested to read that a “Mortar Ballistic Computer” is (or at least was) available for download on the App Store (designed for iPhone, compatible with iPad!)

Being involved more and more in “low intensity” conflicts (without HE support) or with restrictive Rules of Engagements (RoE) that severely limit the access to HE support, the infantryman needs to be able to engage opposing forces at longer ranges than previously thought (up to 600 m for point targets), and fix them or limit their mobility up to 800 m (area targets).

The debate over whether these engagement distances should be achieved by the Individual Weapon or left to “collective” weapons like the DMR and LMG is still open, but the weight and recoil of the 7.62 mm ammunition in its current incarnation militate against its use in a lightweight Individual Weapon, hence the mix of 5.56 mm and 7.62 mm weapons in the same fire team.

The French military experimented with a high-tech grenade-launcher for the same reasons the US did:

In the 1950s, the answer to the low hit probability of the average soldier at ranges higher than 100 m was the ”controlled dispersion” concept of full-auto fire, leading to the reduced-recoil 5.56 mm round.

The difficulty in implementing this concept (the recoil of the 5.56 mm round was still high enough to induce too much dispersion in a lightweight rifle), led to a shift from a burst of multiple kinetic energy projectiles to the use of a single high-explosive, fragmenting round, the fragmentation pattern taking care (at least on paper) of aiming errors.

The PAPOP project (Polyarme-Polyprojectile, similar to the US OICW) launched in June 1994 was intended to combine grenade launcher (for long range engagements) and a “kinetic energy” system for engaging targets at shorter range.

[...]

The project did not go very far, as the weight of the combined weapon was found to be too high and the grenade carrying capacity too low.

The effective casualty radius of air-bursting grenades was also found to be very small (between 14 m² against unprotected standing target and only 4 m² against protected prone target in the most favourable case of the 35 mm grenade), and very sensitive to bursting height & grenade falling angle. All in all, it was found that in order to be effective, the detonation of air-bursting grenades needed to be triggered with an accuracy of ~1 m in both range and direction, and 0.5 m in height, an unreasonable expectation for a hand-held weapon on the battlefield.

It should be pointed out that due to their low velocity, grenades are a very different beast than bullets and that without the help of a laser rangefinder, aiming errors with a grenade launcher are a full two orders of magnitude higher than for a rifle, nearly negating all of the benefit of the large casualty radius produced by the grenade fragmentation warhead at long range.

According to US results, the typical range estimation error for trained soldiers is around 30%, so for a target at a “true” distance of 288 m (for example), even a trained soldier will hesitate between the 250, 275, 300 and 325 m setting on his grenade-launcher sight (an average miss distance of 25 m before even taking into account the intrinsic weapon dispersion, compared with a typical grenade effective radius of 5 m to 10 m), and will need to “walk his fire” to the target at range longer than 150 m, a very difficult task with single-shot grenade launchers.

Even with a tripod-mounted laser rangefinder, operated by a trained spotter in a prone position, the average range error measurement is around 5% of the distance, and could be as high as 9.3%. At 600 m range, that’s an average error of 30 m, much more than the expected casualty radius of this class of warhead.

Typical defensive hand grenades that use a very simple (compact and lightweight) fuse weigh in between 400 g and 500 g, and have a reported casualty radius of around 10 m, so it is doubtful that a 20 mm to 40 mm spin-stabilized grenade with a weight between 100 g and 200 g could achieve a much better casualty radius.

If the same range measurement error could be achieved with a hand held (or shoulder held) device, combined with a 5 m to 10 m effective radius grenade, then a 300 m practical range could be claimed, but a 600 m practical range will require the measurement error to be halved.

The Hitchman report paved the way, Emeric Daniau argues, for numerous studies that tried to evaluate the rifleman’s effectiveness under what was considered “realistic” stress conditions and tried to provide a technical answer to the perceived lack of effectiveness at ranges longer than a hundred meters:

The founding idea of those studies (like ORO-T-160, but also SALVO I & II, SAWS and several others) was that “only bullets that hit count”, and that the only military effect of small-arms fire (and Individual Weapon fire in particular) was hitting and disabling a target. Suppression effects that are known to greatly reduce enemy fire effectiveness and enemy movements (two very interesting military effects) were simply not taken into account and no effort was made to try to evaluate them, or incorporate results of other studies devoted to such topics.

This idea of limiting the effectiveness of small-arms fire to hitting and disabling enemy soldiers immediately calls upon past visions of glorious battlefields where dense masses of soldiers were shooting at each other, or where a handful of brave souls stand against a “human wave” assault of mechanized infantry (“high density” battlefields), but seems totally remote from the “low density battlefields” so frequently encountered during “decolonization” wars or peacekeeping / stabilization engagements.

From a methodology point of view, this choice (deliberate or not) to reduce military effectiveness of Individual Weapon fire to “bullets that hit” had major implications. First, the complexity of evaluating small arms effectiveness was greatly reduced, “scientific” evaluations could be performed and focused on hit probability (p_H) and terminal effectiveness (p_I/H) against unprotected targets, or after defeating personal protection (but not intermediate barriers).

Second, since the maximum effective range considered (300 m) is relatively short, almost any bullet pushed fast enough could do the assigned job (hitting and delivering “sufficient” terminal effectiveness).

Of course, the capability to hit something is very valuable, but what is the hit probability of a soldier in a real combat, as opposed to simulated combat?

The “shots to casualty” ratio of small-arms fire is a highly debatable issue, and numbers as high as 100,000 have been quoted, but without a strong database to sustain that claim.

More reliable values could be found in the experience of the First Australian Task Force (1ATF) during the Vietnam war, with (mean) values of 187 shots per casualty for the 7.62 mm SLR and 232 shots per casualty for the M16 in the context of day patrol.

Nearly 80% of those engagements took place at ranges shorter than 30 m, not really long range, and still the average hit probability was around 0.5%, compared to a hit probability of ~100% found in ORO-T-160.

Of course, “mean” values are only average and in particular events close to “ideal” shooting scenario, shots-to-casualty ratio around 30 to 1 were achieved. While this number (p_H ~3%) is definitively higher than 0.4% or 0.5% (nearly one order of magnitude), it’s still a very substantial difference from results commonly found during simulated combat.

The French operation in Mogadiscio in June 1992 could be seen as a very good example of effective firing, but even in this scenario ~3500 small arms (5.56 mm and 7.62 mm) rounds and ~500 12.7 mm rounds were expanded to produce a maximum of 50 casualties (p_H of 1.25 %).

Police shootings that take place at very short range (generally less than 7 feet) exhibit the same symptoms of very low hit probability, one or two orders of magnitude less than expected. For example, during the famous 1997 North Hollywood shootout, the two heavily armed bank robbers fired approximately 1100 rounds during a 44 minutes battle and wounded 11 police officers (p_H ~1%) and 7 (probably untargeted) civilians.

In return, police officers fired an estimated 650 rounds and killed both perpetrators (it is possible that one committed suicide after being wounded). Both bank robbers wore homemade bulletproof garments and one was hit several times in rapid succession in his legs until he surrendered (he died later from blood loss), so it’s difficult to evaluate the hit probability of the law officers, but even at a few feet, with good visibility and superior training (the final part of the shootout was conducted by SWAT members at a distance around 3-4 meters), one should expect results probably not much higher than 5% to 10%, again a substantial difference between “real life” results and results recorded during simulated combat.

This difference could be easily explained because of course, during simulated combat, no matter the amount of “realism” of the shooting scenario (sounds, fumes, explosions, fatigue or even electric shocks on the shooters), the targets are not returning fire so soldiers could focus on “clearing the range” (and freely expose themselves during the process), while during real combat trying to minimize exposure time to avoid being hit is mandatory.

So, if we look back at Figure 30, we have an idea of the hit probability of a soldier firing his M1 rifle at a human-size target with an exposure time of 3 seconds.

In order to be able to hit this target, the soldier needs also to expose himself to incoming fire (from his target, or from other people waiting for a shot of opportunity, the battlefield is not a place for a duel) during roughly the same amount of time.

[...]

Evaluating the dispersion of hand-held weapons and trying to improve the hit probability was at the heart of both ORO-T-160 and ORO-T-397 (Salvo II study).

Most results found in ORO-T-160 used a target exposure time of 3 seconds and shooters were discriminated between “experts” (highest skill) and “marksmen” (lowest skill).

During those tests, “experts” scored significantly higher than “marksmen” (another “argument” against long-range firing in the hands of the masses). For example, during the second test, “experts” scored 8 hits (25% hit probability) on a man-size target at 310 yards (Figure 33), when “marksmen” scored only 2 hits (6% hit probability, Figure 34).

During those test, a large cloth was used to record as many shots as possible (hits and near-misses), and it’s interesting to notice that in both cases:

• the number of shots recorded was nearly the same (25 for “experts” and 26 for “marksmen”),
• the dispersion of shots was nearly the same (~7.25 mils for “experts” and ~7.5 mils for “marksmen”),
• the number of rounds impacting in a 1 m circle around the head of the target was the same (23 shots, or 72%, in both cases), the only significant difference is the mean point of all impacts, “on target” for “experts” and slightly off target by 35 cm for “marksmen”, this shift of MPOI alone explains the difference between a hit probability of 25% and 6%. A deviation of 35 cm (~14 inches) at 310 yards is what you can expect from a 15 mph lateral wind acting on the .30-06 M2 bullet,
• a third test was performed, using a 1 second target exposure time and a random schedule between two targets, one located at 110 yards, and one located at 265 yards (table A3 in ORO-T-160, p.100), and under those firing conditions the “marksmen” greatly outperformed the “experts”. Unfortunately, results obtained during this third test were not reviewed as deeply as results obtained during test n°1 and n°2, and no conclusion was drawn from it.

That last point makes it clear that we weren’t training riflemen to shoot quickly.

During the SALVO II study (ORO-T-397), a similar test was performed. The dispersion of each individual soldier was measured (“Experts”, mean dispersion between 1.97 mils and 2.93 mils; “Sharpshooters”, mean dispersion between 2.12 mils and 3.67 mils; “Marksmen”, mean dispersion between 2.30 mils and 3.70 mils) and from the conclusions of this report, it is clear that the level of marksmanship (for a given training program) plays only a small role in hand-held weapons dispersion compared to target exposure time and visibility (Figure 35).

The 7.5 mils and 7.25 mils obtained for “marksmen” and “experts” respectively, for a target exposure time of 3 seconds found in ORO-T-160 (published in 1952) are close to the “upper bound” found in ORO-T-397 (published in 1961) and probably reflect the change of marksmanship training (TRAINFIRE I was introduced in 1954, and TRAINFIRE II in 1957), from “bull’s-eyes” targets to “popup” targets.

Mean dispersion found in ORO-T-397 was around 3 mils for a target exposure time higher than 5 seconds, and this dispersion was increasing as the exposure time was decreasing, up to 7–7.5 mils (24 MoA to 26 MoA).

[...]

So, there is a wide difference between the way we evaluate small-arms hit probability and “real-life” results which seem to range from 0.3% to 3%, even at fairly close distances. From an individual fire perspective (one soldier, one target and one bullet), this value could be considered low, but from a tactical point of view, with tens to hundreds of soldiers, each carrying more than a hundred rounds, it’s high enough to produce decisive military results.

For example:

• during the battle of Magersfontain in December 1899, fire from the 8,500 Boers’ individual weapons (Mauser bolt action rifles) at a range of around 400 yards (366 m) was sufficient to kill and wound 665 British soldiers (24.5% of the total) in the first 10 minutes of the battle,
• a few days later, during the battle of Colenso, 2 British batteries (12 guns) of field artillery were engaged by rifle fire at a distance of 700 m. Suffering heavy casualties, the British were forced to fall back to their camp, losing 10 guns in the process.

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The adoption by the US, followed by NATO, of the .223 Remington cartridge as the 5.56 x 45 mm, was not the result of concluding that the battlefield depth (measured in kilometres before WWI) was now reduced to 300 m, but an acknowledgement that effective HE support could be provided now at very short range in most conditions, and that the fire delivered by the infantry individual weapon should be used only for defeating adversaries in the 0 to 300 m bracket, longer ranges being devoted to collective weapons firing heavier ammunition.

While looking toward a 600-meter lightweight general-purpose cartridge, Emeric Daniau traces the history of individual weapons and notes how their role has changed:

Against large bodies of troops moving in compact formations (as in, for example, the Transvaal campaign), more than 50% of firefights occurred at what we now call “long range” (between 900 m and 2100 m); only 25% occurred at ranges shorter than 900 m (Figure 2).

According to J.B.A. Bailey, in the sixty years preceding 1914, artillery fire produced less than 10% of all battle casualties, the remaining 90% fell to small arms (mostly individual weapons), whose range and accuracy had come to rival those of artillery. This estimation is supported by medical and after-battle reports available from that era.

But the introduction of shells loaded with high-explosives (instead of black-powder) around 1890, the invention of reliable impact fuses, the development of rapid-firing guns like the famous French 75 mm Mle 1897 (with an oleo-pneumatic recoil-absorbing mount) and mathematic models for direct and indirect fire solutions (increasing dramatically the hit probability of long-range gunnery) during the same period radically changed the way armies were fighting, and it was anticipated (in 1901, long before WWI) that artillery fire could produce as much as 40% to 50% of overall casualties in future Europeans conflicts.

[...]

WWI saw (indirect) artillery fire replacing (direct) long-range small arms fire in its battlefield effectiveness and this trend continued well after the end of the war. During WWII, small-arms fire including individual weapons and machine guns) produced no better than 2/3 of enemy casualties (when fire support was lacking) and sometimes even less than 1/3. With effective long range fire achieved by HE effects (artillery, tanks and planes), there was a huge pressure to reduce the practical range of weapons (or at least, no need to try to increase it) in order to increase still further the practical RoF.

[...]

In the US, the experience of infantry engagements during WWII and the Korean war (both high intensity wars) was reviewed and the famous “Hitchman” report concluded that since most (~90%) infantry engagements occured at a maximum range of 300 yards (274 m) and hit effectiveness with US M1 Garand rifle was “satisfactory” only up to 100 yards (91 m), a way to increase the individual weapon overall effectiveness (up to 300 yards) was to reduce the bullet and cartridge weight and use a pattern dispersion” principle (controlled burst fired in full-auto mode) to compensate for human aiming errors.

“3. To improve hit effectiveness at the ranges not covered satisfactorily in this sense by men using the M-1 (100 to 300 yd), the adoption of a pattern-dispersion principle in the hand weapon could partly compensate for human aiming errors and thereby significantly increase the hits at ranges up to 300 yd.” (conclusion of the ORO-T-160 report).

It should be stressed that for the authors of the ORO-T-160 report, semi-auto fire was to be used only at short range (less than 100 yards), and “pattern-dispersion” full-auto fire reserved for ranges longer than 100 yards, the opposite of the current thinking of the effectiveness of full-auto fire and an indication that there could be some difference between the concept of “pattern dispersion” and the real realisation as found in current assault-rifles.

The addition of a toxic agent to the bullet (to increase the lethality) was also proposed.

The parallel work on a small-calibre, high velocity (SCHV) cartridge, using a 5.56 mm bullet launched at a very high velocity (1030–1200 m/s) indicated that a large reduction in ammunition weight and recoil could be achieved without decreasing hit probability or incapacitation capability against dismounted soldiers.

Before the Hitchman report, infantry fire was mostly considered as a form of “collective fire”, but after WWII infantry fire effectiveness was often considered only from the point of individual fire, aimed at individual targets, and “collective fire” was replaced by MG fire.