[ This article was written by Sven Ortmann of Personal Defence Weapons Central, an excellent small arms resource. ]

by Sven Ortmann, lastdingo@gmx.de, 2008-01-05

There are too many misleading anecdotes and rumors about military rifle calibers floating in the air (and in the WWW). This short article is meant to help readers with a presentation of the results of my secondary source research on the rifle caliber discussion and terminal (wound) ballistics.

Caliber: 9×19 mm and .45ACP (= 11.43x23mm)

This is the standard NATO caliber for pistols and a popular caliber for submachineguns. The only ones who seem to have a strong dislike for this caliber seem to be those U.S. Americans who continue to compare it with .45ACP.

The U.S. American problems with the 9x19mm caliber seem to include a mix of emotions (a Colt M1911 in .45ACP feels much more powerful) and poor quality of the U.S. standard issue 9mm pistols. The latter is as far as I know more a magazine production quality problem than a pistol design problem. The origin of .45ACP is said to lie in combat experience around 1900 in the Philippines where determined Philippinos weren’t stopped reliably by smaller revolver calibers. Tests on live animals in 1904 showed better effects for heavier bullets, but little improvement with velocity. Bullet design has improved a lot since then, and hollowpoint bullets that flatten their nose in soft tissue to increase their diameter are much more effective than simple soft lead bullets. A good 9mm bullet enjoys a similar advantage over a .45ACP soft lead bullet than the latter over a 9mm soft lead bullet. There’s a fundamental problem, though: There’s not much difference in effect on the target if you hit the wrong places and the permanent cavities of pistol bullets are all relatively small. Many body parts are simply not essential enough – their destruction doesn’t stop a determined opponent immediately; no matter whether you hit with .45ACP or 9x19mm.
A new procurement of pistols could easily be a significant improvement over existing 9x19mm service pistols, though. A new pistol could be designed to use reliably both standard 9x19mm and “hot” 9x19mm loadings (higher pressure). The latter would give some extra punch, especially extra penetration. A further improvement is possible by procurement of better bullets. The Russians have a 9mm semi-jacketed exposed steel core bullet that combines AP effect (hard core) with a hollow-point effect (outer parts of the bullets deform and effectively increase the bullet diameter in soft tissue). Such a bullet has enough penetration capability against a combination of a full pouch and a light kevlar vest. An improvement of pistol accuracy is probably more pressing than the caliber; some sort of shoulder stock and easily visible sights (large iron sights as usual on revolvers, for example) could help.

Caliber: 5.56x45mm NATO

This caliber is at the center of a great and long-lasting controversy. Its opponents call it a varmint caliber and report firefights with multiple hits on the same opponent without satisfactory effect. They compare this caliber very often to the supposedly more effective 7.62x51mm caliber. More about that in the 7.62 chapter. Another problem with 5.56x45mm is its rather unsatisfactory ability to penetrate wooden or wall covers. A dissatisfaction with the standard service rifles/carbines of both the USA and the UK (the British solved their problems with an extensive upgrade) and the use of rather short barrels in the U.S. M4 carbine add to the problems with 5.56x45mm.

The defenders of the caliber remind us that even mutilating wounds by much larger calibers and even explosive warheads cannot reliably stop a determined opponent.

The most terrible problem in the 5.56x45mm caliber discussion is the use of anecdotes. Different barrels, ranges and hit locations produce very different effects, so you will always find anecdotes to support your position on this caliber – no matter what’s your position.

There’s (apparently especially in Germany) a stupid rumor about 5.56x45mm and rifle calibers in general that tells about a nervous shock that can kill even with only small injuries. It’s nonsense. A short primer on rifle/carbine bullets; they behave differently in soft tissue than most pistol bullets. They don’t move straight through the tissue all the way. Instead, they begin to turn and usually exit bottom forward. Some bullets break up under the stress of this turn, and the fragmentation increases the destruction of soft tissue very much. A turning bullet doesn’t create a permanent cavity of much greater diameter than its own length; a disintegrating bullet can create a much, much larger permanent cavity.

The ideal rifle/carbine bullet looks like this; it’s able to penetrate cover/armor, it begins to turn in soft tissue immediately and it disintegrates into fragments with devastating effect in soft tissue (terminal ballistics). Good sectional density and ballistic coefficient are important for a good effective range (external ballistics). Finally, some people want it to be lead-free to protect the environment and save costs on shooting range maintenance.

So what does a 5.56x45mm bullet really do? Answer; it depends.

The differences between 5.56mm bullets are noteworthy in terms of cover penetration (heavier is better), but all seem to share a rather disappointing “performance” in soft tissue. The bullet begins to turn later than desired. This means that frontal hits on skinny opponents are often not very effective because the most destructive part – the turning and possible fragmentation – happens too late (the 180° turn isn’t completed before exit).

The other problem in soft tissue is fragmentation. Fragmentation is necessary to achieve a good deal of damage with the small bullet. This requires a good impact velocity and appropriate bullet design. Short-barrelled weapons don’t accelerate the bullet to the originally intended velocity, and the velocity drops rapidly with the distance. 5.56x45mm fired from carbines like the M4 carbine produce very little if any fragmentation in soft tissue at distances greater than about 50-100m.

Carbines and assault rifles should be effective to at least 300m, squad sharpshooters (also known as Designated Marksmen) and light machinegunners should be highly effective out to 400m with good effect. 5.56x45mm doesn’t offer much effect in soft tissue at many relevant ranges unless fired from long barrelled weapons. Barrel lengths of at least 18″ or at the very least 16″ are often recommended. The original M16 assault rifle and many other assault rifle with this caliber have a barrel length of 20″ while the M4 carbine has only a 14.5″ barrel.

There’s apparently not much potential for improvement in the 5.56x45mm caliber: Heavy bullets for improved cover penetration and long barrels for reliable fragmentation seem to be somewhat successful approaches.

Caliber: PDW cartridges (5.7x28mm and 4.6x30mm)

These calibers share the same problems as 5.56x45mm, just even more so (they don’t seem to break up at all).

The short story is like this: Weapons in these calibers are easily controlled in full auto fire due to the low impulse of the cartridges (light bullets). The individual bullets don’t do much to soft tissue (but more than you would tolerate in your own soft tissue).

The strength of these calibers is the higher hit probability (especially for ill-trained support troops) in comparison to 9x19mm and .45ACP. The higher hit count might make up for the lesser effect of individual bullets. A one-vs-one comparison of the wound ballistic effects is therefore misleading. More hits also add to the chance of hitting something really vital.

There are other, less well-known calibers for PDWs (personal defence weapons) than these two. Some use larger calibers, but they’re likely all either similar to my description of pistol or PDW caliber wound ballistics.

Caliber: 7.62x51mm NATO

This is another NATO standard caliber (forced on NATO by the USA against a clearly superior British design). It has been replaced as assault rifle caliber by 5.56x45mm almost completely and was never a carbine caliber. 7.62x51mm is still very widespread as machinegun caliber in NATO armies and is also in use with some sniper/sharpshooter rifles.

The caliber was too powerful for controllable assault rifle full auto fire (well, controllability in bursts was OK within hand grenade range). The cartridges are quite heavy and it’s difficult to carry many of them into action; a major disadvantage for suppressive fires unless you need to suppress enemies who are behind light cover.

The penetration of cover is usually satisfactory, but armor penetration isn’t very good for the simple reason that almost all gunshields, armored vehicles and even some heavy body armor were designed to withstand this caliber and its Russian counterpart, 7.62x54mmR. Only expensive SLAP cartridges (saboted light armor penetrating, performance in soft tissue) have a very good penetration capability at short and medium range.

The external ballistics are under criticism for sniping and more powerful calibers (.300WinMag, .338LapuaMag, 9.3x64mm and even .50BMG, for example) with less bullet drop and less wind sensitivity have become important in sniper rifle procurement since the 90’s.

7.62x51mm is often being attributed with a huge and rarely questioned power against soft targets; knockdown power, manstopping power – no matter how they call it. 7.62x51mm is usually presented as the good example in comparison to 5.56mm. This is – at least for U.S.-made 7.62x51mm standard service cartridges – not fully justified. There are significant differences in penetration till the turning movement begins and in fragmentation. The U.S.-made (standard issue) 7.62 bullets aren’t that much better than 5.56mm bullets (if better at all). They penetrate deeply before turning and don’t fragment much.

There have been much superior (at least in fragmentation) bullets in service (like the German ones) and there’s also a 7.62x51mm cartridge/bullet design that fulfills all expectations for soft tissue damage; it begins to turn and fragment very quickly and has a reliable and devastating effect on soft tissue.

Again; you won’t necessarily stop a determined enemy from firing at you if you don’t hit the right spots – no matter what rifle ammunition you use.

Caliber: .50BMG (= 12,7x99mm NATO)

This caliber is widespread and has loyal fans in the USA and also elsewhere, but it wasn’t adopted in some NATO forces and has some drawbacks.

It was originally a tank-penetrating caliber for machine guns (M2 Browning, later M2HB). Similar cartridges were used during the World Wars by anti-tank rifles (which were only able to penetrate light armor plates). Tanks got thicker armor plating by the mid-1930’s, leaving only light armored vehicles and certain vulnerable spots on heavier armored vehicles as vulnerable to .50BMG. This application has been revived in the 1980’s for long-range and “anti-material” sniping.

There’s no very lively discussion about this caliber in the public. Attempts to replace it focused on intermediate sniping cartridges for long-range and armor-penetrating sniping (like .338LapuaMag), 40x54mm HE cartridges for automatic grenade launchers that replaced many M2HB (.50BMG) machine guns on vehicles and finally a high-tech 25mm air-burst HE cartridge in the failed OCSW program.

The primary problems of .50BMG are weight and volume. Both ammunition and weapon are much bigger than their 7.62x51mm counterparts. The ammunition supply for a .50BMG is usually very small in comparison to the 7.62x51mm alternative. .50BMG is also too heavy for dismounted machine gun use on the move; it can be done (with a tripod), but the effort isn’t justified in most situations.

This caliber is probably only justified if the extra penetration is really necessary. One example: Reconnaissance vehicles need to be able to take on enemy reconnaissance vehicles which are usually armored against 7.62x51mm AP, so something heavier is desirable even for the lightest recce vehicles.

An intermediate machine gun caliber close to the .338LapuaMag sniper cartridge could match the utility of .50BMG in most situations with significantly more ammunition for the same weight and volume.

Both .50BMG and 7.62x51mm are quite well-established and not much under criticism, so there’s no good reason to expect a new, intermediate caliber standard for machine guns.

Ideal caliber discussions

The “ideal” infantry rifle caliber needs to be suitable for rifle, carbine, light machine gun and possibly even squad sharpshooter and medium machine gun applications. Penetration is important, bullet drop and effect at ranges like 400 or 500m is important, soft tissue damage needs to be good and consistent at all ranges and both weight and volume need to allow for a good ammunition load.

Historical and recent conclusions about an ideal infantry caliber almost always agreed on a calibre in the range from 6 to 7 mm. The larger ones tend to have better effect and to be heavier while the smaller calibers in that range tend to offer superior external ballistics (flatter trajectory, more useful at long range).

The optimum is probably close the the center; a 6 or 6.25mm caliber would probably be too close to 5.56mm to convince the 5.56mm critics (maybe for good reasons).

The 6.5mm Grendel and 6.8mm SPC calibers have become famous in the last few years as optimal caliber candidates. Both use conventional cartridge technology – it may be that confidential details from plastic case technology development would favor something like a 6.5-6.8mm plastic cased cartridge instead.

Links for additional reading (and graphics)

There are thousands of possible links, but most would lead you to misleading information.

http://www.rayguncharlie.net/sr/basics/pmrb.html

http://www.dtic.mil/ndia/2008Intl/Roberts.pdf

http://www.firearmstactical.com/wound.htm

http://www.recguns.com/Sources/IVF1.html

http://www.angelfire.com/art/enchanter/PDWdebunk.html

Keep in mind at this link that bullet technology has advanced significantly since 1904:
http://www.angelfire.com/art/enchanter/1904trial.html

http://www.angelfire.com/art/enchanter/pigboard.html

Bullet categories:
http://world.guns.ru/ammo/bullets-e.htm#sjesc

An overview over PDWs:
http://www.personaldefenceweapons.com