The Definitive Military Service Calibre and Rifle For the 21st Century - Part 1

By Mike Staples


Hi, my name is Mike Staples and I am an ex Australian Army Fitter Armament or to put it more simply, an Armourer. My experience takes in all Australian Military Weapons including pistols, rifles, SMGs, LMGs, HMGs, Mortars, recoilless rifle, and artillery pieces, as well as mounted guns in our Armoured vehicles that were current at the time of my service. On top of that experience is my love of shooting, which started when I was around 6 years of age and has continued to this day, some 51 years later. I have been asked by Mr. Hawks to write an article on a suitable calibre for a General Purpose Military Rifle (GPMR), and whilst the calibre is important the delivery system, a.k.a. the rifle, is equally so. That being the case, this first article will establish what I feel is a suitable calibre to replace the 5.56mm NATO round, whilst the second part will put forward suggestions on a suitable rifle.

There has been a multitude of cartridges that have been used by the worlds Military Forces, and to compare all of them in the pursuit of the "perfect calibre" for the 21st Century would take many pages and many hours of research. Therefore, I will concentrate on those which have been used by the US, Australia, Great Britain, and NATO Forces in recent history.

Since the Vietnam War there has been a move to make one calibre "the NATO calibre," and at this point in time that calibre is the 5.56mm NATO. The main reason for this, from my perspective, is to make all aligned forces users of this calibre. NATO is a collage of many countries. When NATO forces either take up arms against an aggressor or have become an occupation force on behalf of the United Nations inside a country that has experienced a war or uprising, many soldiers from different countries make up that force. If all used a different calibre in their GPMR, ammunition re-supply would be a nightmare.

The question is then, "What makes a suitable calibre and why?"

The answer to this question will not be easy to establish, as every country and every soldier has a differing opinion. While some like one calibre and one style of rifle, others have trouble accepting those choices. They may prefer to stay with whatever their country uses, as it has become familiar, comfortable and a trusted friend.

I am told by Mr. Hawks and some of my Australian Army friends that there are moves afoot to abandon the 5.56mm calibre. (These may, of course, come to nothing--particularly as they originated with the troops, not the high command. -Ed.) Apparently the U.S. Senate is currently considering a new calibre (the 6.8mm SPC) for use by Special Forces. As the actions of the U.S. military have in the past greatly influenced the NATO countries, it is quite likely that whatever is chosen by the U.S. will eventually become the NATO standard.

Before they do, I would like to bring to the attention of the leaders of the NATO countries a calibre which is not only a suitable upgrade, but that eclipses the two best service rounds yet devised.

To do this I must compare the two standard NATO rounds used today (7.62x51mm and the 5.56mm) with what I consider to be the best choice. I will include in these comparisons the .30-06, a world record holder for all ranges prior to the advent of the .308 Winchester (7.62x51 NATO) and which was, over a number of decades, the U.S. calibre of choice.

The .30-06 was brought out in 1906 to replace the original cartridge for the Springfield rifle of 1903, which initially was chambered for the .30-03 round. Both cartridges fired a .30 calibre bullet, but the '03 had a 220 grain monster and a very long neck to accommodate it. The neck of the '06 case was shortened by .07 of an inch and became the standard military cartridge with a 150 grain spitzer projectile. The '03 and '06 signify the year of first use.

This round was used in every .30 calibre weapon in the US armoury up until the late 1950s. These included the M1 Garand, the BAR and their main LMG, the .30 calibre machine gun. At that time the .30-06 was replaced by the ballistically identical but 10% smaller .308 Winchester (7.62mm NATO) cartridge.

Why they ever abandoned these powerful cartridges, exchanging them for the .223 (5.56mm) "squib" used in the M16 Armalite rifle, is anybody's guess. (The official reasons included reducing recoil and facilitating fully automatic fire. -Ed.) That change, as far as I am concerned, did the US soldier a great disservice. More on that in the second part of this article.

Detailed tables will establish my calibre of choice and the reasons for it. The calibres I will compare in this article are as follows:

(1) .30-06 (US design) - .30 calibre, .308" projectile (military calibre)

(2) 7.62 x 51 (.308 Win.) - .30 calibre, .308" projectile (military calibre)

(3) 5.56mm (.223 Rem.) - .22 calibre, .224" projectile (military calibre)

(4) .270 Winchester - .270 calibre, .277" projectile (civilian calibre)

Before I proceed, I would like to clarify "calibre" and the fact that some projectiles appear to be the same size as the calibre.

Calibre is described as being "bore" diameter (inside bore diameter, ID), which is gauged across the lands of the rifling in the bore of a weapon. The diameter of the projectile is usually equal to the "groove" diameter of the bore, measured across the depth of the groves in the bore (outside bore diameter, OD), or in some cases is slightly bigger than the OD of the bore.

This difference, if the projectile is slightly bigger than the distance across the grooves, is possibly only 1 or 2/1000ths of an inch. This is ordinarily only the case when the projectiles are made from a lead-antimony mixture, as these projectiles are soft enough to deform sufficiently to allow the projectile to fit the barrel. I would suggest that all copper clad (jacketed) projectiles would be the same size as the OD of the bore. To be effective, all projectiles must, at the time of firing, "take" the rifling of the weapon, making a gas tight seal.

Some common examples of this differentiation in calibre are the .308 Winchester and the .243 Winchester. The .308 Winchester is in reality a standard .30 calibre cartridge. .308 rifles have a bore diameter of .300" and a groove/bullet diameter of .308". (Both dimensions are identical to the earlier .30-06 and .300 Magnum.)

The .243 Winchester is a similar case and rifles in this caliber have a groove/bullet diameter of .243". Both the .243 and .308 were named for their groove diameter rather than the more traditional bore diameter. This method of nomenclature became popular after the 1950's and many, but not all, cartridges developed since that time have been named for their groove/bullet diameter.

To arrive at a suitable calibre for a GPMR one must take into consideration the following minimum criteria:

(1) Does the selected calibre have minimal bullet drop at ranges out to a minimum of 400 yards (366 metres)?

(2) Is the complete round suitable for self-loading rifles (in overall length)?

(3) Is the projectile heavy enough to deliver sufficient knock down power (Kinetic Energy) at all ranges out to 400 yards?

(4) Will the trajectory of the projectile be relatively flat when compared with other suitable ammunition?

(5) Is a complete round (i.e. cartridge case + projectile + powder + primer) light enough to allow a soldier to carry a minimum of 300 rounds on his person?

(6) Will the selected calibre and projectile be accurate enough to shoot groups of 5 inches/125mm or less at the stipulated minimum range? (The rifle being used will be a factor here.)

(7) Will the selected calibre and projectile be able to attain velocities of at least 3000 FPS from a self loading service rifle?

The following tables clearly demonstrate what round I feel conforms to the above criteria. The comparison rounds are:

(1) The 5.56mm round, using a 63 grain projectile with a MV of 3200 FPS.

(2) The 7.62 x 51 round, using 168 grain projectile with a MV of 2700 FPS (I do not have detailed tables for a MV of 2650 FPS, so I have used a slightly higher MV to highlight the differences).

(3) The 30.06 round using a 150 grain projectile with a MV of 2700 FPS.

(4) A .270 (6.858mm) round using a new case with the same dimensions as the 7.62 x 51 case, except it is necked down to accept a .277" diameter projectile. (A similar situation to the .243, which uses a necked down .308 case). In European (or modern military) nomenclature this would be a 6.85 x 51mm cartridge. 150 grain bullet at a MV of 3000 FPS.

Note: All projectiles are spitzers (pointed) with boat tail base, as I have no tables for FMJ projectiles. All tables, are based on information, as found in the Sierra Reloading Manual, 2nd edition; Sighting plane is assumed to be 1.5 inches above the axis of the bore; All distances are in YARDS. 1 Imperial Yard = (approx.) 0.9143 metres.

Velocity in feet-per-second (Muzzle, 100, 200, 300, 400, 500 yards)

5.56mm NATO (63 grain): 3200, 2862, 2521, 2198, 1900, 1612

7.62 NATO (168 grain): 2700, 2513, 2333, 2161, 1996, 1839

.30-06 (150 grain): 2700, 2473, 2257, 2052, 1859, 1664

.270 Win. (150 grain): 3000, 2804, 2613, 2429, 2253, 2084

Kinetic Energy in Ft-Pounds (Muzzle, 100, 200, 300, 400, 500 yards)

5.56mm NATO (63 grains @ 3200 FPS): 1432, 1146, 889, 676, 505, 364

7.62 NATO (168 grains @ 2700 FPS): 2719, 2355, 2030, 1742, 1486, 1261

.30-06 (150 grains @ 2700 FPS): 2428, 2037, 1697, 1403, 1150, 922

.270 Win. (150 grains @ 3000 FPS): 2997, 2618, 2273, 1965, 1690, 1446

Bullet Drop from line of bore (at 100, 200, 300, 400, 500 yards)

5.56mm NATO (63 grains @ 3200 FPS): -1.76, -7.79, -19.31, -38.06, -66.51

7.62 NATO (168 grains @ 2700 FPS): -2.37, -10.23, -24.47, -46.14, -76.53

.30-06 (150 grains @ 2700 FPS): -2.41, -10.51, -25.42, -48.60, -81.86

.270 Win. (150 grains @ 3000 FPS): -1.90, -8.22, -19.63, -36.92, -61.05

Bullet Path in Inches at Zero Range of 300 yards (100, 200, 300, 400, 500)

5.56mm NATO (63 grain @ 3200 FPS): +3.68, +4.58, 0.00, -11.81, -33.33

7.62 NATO (168 grain @ 2700 FPS): +4.79, +5.58, 0.00, -13.02, -34.75

.30-06 (150 grain @ 2700 FPS): +5.06, +5.94, 0.00, -14.20, -38.49

.270 Win. (150 grain @ 3000 FPS): +3.36, +4.36, 0.00, -10.25, -27.33

As the above tables clearly demonstrate, the 5.56mm NATO round is as suggested a "squib" and has precious little remaining energy beyond 200 yards compared with the other calibres, and I feel that this is a generous assessment. Its bullet drop characteristics are better than the projectiles of the 7.62 and .30-06, and it shoots flatter than both. But, lacking their knock-out punch, so what?

On the matter of accuracy with the 5.56 NATO round, I would dispel a myth that was rife in Vietnam. That being the projectile "tumbled" or rotated in an ellipse fashion along its axis. This assumption was made by many soldiers because of the damage the projectile could inflict at short range.

The reality is that any sharply pointed FMJ bullet may tumble if it hits something hard enough to destabilize or deform it, a large bone, for example. This tumbling effect has been noted by US troops ever since the adoption of the .30-06 cartridge and its 150 grain spitzer bullet in 1906. It is not unique to the 5.56mm bullet. But often a FMJ bullet will simply drill a bullet diameter hole straight through the target, particularly in soft tissue. The terminal performance of any FMJ spitzer bullet is unpredictable and any result other than a caliber diameter hole cannot be relied on.

Both the .30-06 round and the 7.62 x 51 round perform very well at all ranges out to 500 metres, with sufficient energy to stop most men in their tracks. I read some years ago that a rouge African Elephant was shot and killed at a range of approximately 100 metres with an FMJ 7.62mm NATO round. Before WW II many elephants and other heavy game were killed at fairly close range by .30-06, .303 British, and 8mm Mauser FMJ bullets.

Both the .30-06 and 7.62x51 are very accurate rounds, especially in bolt action or single shot rifles, as their target shooting records attest. There is also the indisputable fact that US snipers in Vietnam (and other theatres since) used the 7.62x51 round very effectively at long range.

I am reliably informed that, whilst the round was a 7.62x51, its similarity to that used in the GPMG M60 and the Australian L1A1 SLR ended there. Each sniper was responsible for handloading their own ammunition and, as their rifles were bolt action repeaters, it's quite possible that different projectiles and powders were used.

One shot kills have been recorded out to ranges of 1200 metres, and that is no mean feat.

I have personally experimented with my Omark single shot, heavy barrel target rifle, which has a Weaver 8 power scope fitted. Using 150 grain Sierra MatchKing HPBTs, IMR-4064 powder and magnum primers I have chronographed projectiles 15 feet from the muzzle at speeds averaging 2900 FPS. I have, on numerous occasions using that rifle and my hand loaded rounds, shot 6 inch groups or better at 800 metres.

If the Australian military and the US Senate are investigating the possible change to a bigger round for their GPMR and section LMGs, then the .30-06 and the 7.62 x 51 rounds should be high on their list.

I would ponder the question, "if they are considering an upgrade of calibre, is that an admission that the 5.56mm round does not stack up against the previously used 7.62x51 NATO round?"

By using the .30-06 and the 7.62x51 cartridges as a bench mark, I have looked for a suitable round that can deliver everything required of a GPMR. The round and calibre are only part of this equation. However, I would point out that once a suitable calibre has been identified a competent rifle can be built around it.

A nearly ideal calibre is the .270 Winchester, which has been around since 1925. The civilian round uses a necked down .30-06 case and has proven to be an excellent hunting calibre. The only problem with this round is its overall length, which can create feed problems in semi-auto and automatic rifles. That being the case, it could cause stoppage problems that can endanger a soldier's life. However, this can be overcome quite simply by the introduction of a new .270 cartridge using the 7.62x51 (.308 Winchester) case.

The .243 Winchester and 7mm-08 Remington cartridges use a necked down .308 case and there is no reason why a new case cannot be made to suit the .277" diameter projectile of the .270. It could be called the .270 Military/NATO or the 6.85x51mm Military/NATO. Its slightly shorter length would overcome feed problems and its overall total weight would make it possible for a soldier to carry upwards of 300 rounds on his person.

The above tables clearly demonstrate that the .270 Winchester calibre outshines the other comparison rounds in all respects and with a slightly lighter (130 grain) projectile in a good rifle, MVs up to 3000 FPS should be achievable.

It is my opinion as an Armourer that kinetic energy and accuracy, at all ranges out to at least 400 yards, should be the base criteria for a calibre suitable for a GPMR. Every time a soldier faces an enemy his target can and does shoot back. Therefore, he must be given every advantage to negate this threat before he or a fellow soldier is killed or wounded.

The figures supplied by Sierra are fairly complex and their calculations are not much better, but the everyday soldier only needs to know the following:

(1) The zero range of his rifle (300 yards/275 metres).

(2) Where he needs to aim to hit his enemy at ranges up to zero range.

(3) The holdover height at ranges beyond zero range, should it be necessary to shoot beyond that range.

(4) He must have an understanding of what kinetic energy is and why it is important to himself as a soldier and the man standing next to him.

(5) Finally he must learn how to estimate distances accurately, unless he has the use of modern range finders or estimators.

In the next article I will marry this round with a tried and proven rifle, which I believe will give our soldiers a decided tactical advantage. It is very necessary for our soldiers to be confident that one round will incapacitate his enemy, without having to throw an entire magazine at him.

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