Infantry Magazine Article Text LinkSmall arms ammunition for the 21st century: high performance alternatives to the 5.56 NATO roundInfantry Magazine, July-August, 2004 by Stanley C. Crist
It has been four decades since the 7.62mm NATO round began to be superseded as the ammunition of choice for U.S. combat rifles when the 5.56x45mm M193 cartridge--and the M16A1 rifle that fired it proved better stilled to the battlefields of Vietnam. When 5.56x45mm ammunition became NATO-standard about 20 years ago, projectile weight was boosted from 55 grains to 62 grains, and the heavier, "green-tip" round was type-classified as M855 Ball in U.S. service.
Accounts from the Vietnam War indicate that M193 amino was very lethal at the relatively short engagement distances encountered in jungle warfare, and could penetrate the walls of typical bamboo huts with ease. However, circumstances were much different when, many years later, Soldiers were again sent into harm's way in the hostile regions of Somalia, Afghanistan, and Iraq.
In Somalia it became all too apparent that the M855 round was lacking the ability to punch through the brick walls and other obstacles commonly encountered in urban areas. As Captain John Hodge related in his article. "The M240B Machine Gun" (Infantry, March-June 1997, p. 8), it was noted that "... while the M249 provided good firepower, in some situations, they needed greater range and penetration power." Equally disturbing were the reports that when M855 ammo was fired from the M4 carbines employed by special operations personnel, it too often required multiple hits to neutralize an opponent, even though many Somali males were of slight build.
These problems were soon magnified as more individuals were armed with the short-barreled, M4-series weapons. Soldiers of the 82nd Airborne and 101st Air Assault divisions had their M16A2 rifles replaced by M4 and M4A1 carbines in the years prior to conducting combat operations in Afghanistan and Iraq. Also, in these traits and others, like the Stryker brigades, the standard M249 light machine gun (LMG) is being phased out in favor of a paratrooper model with a barrel as short as that of the M4 carbine.
While these alterations do result in a weapon that is lighter and easier to handle In the confined interior spaces of infantry vehicles, utility helicopters and urban buildings, terminal performance suffers. The primary mechanism behind the lethality of 5.56mm ammo is the fragmentation that results when the bullet impacts soft tissue at high speed. The truncated barrels do not create sufficient velocity to produce this effect beyond a short distance, nor do they provide sufficient "reach" to engage enemy personnel at the extended ranges encountered in desert and mountain warfare.
Given the trend to acquire lightweight small arms with abbreviated barrels, combined with the inherent limitations of the M855 ball round, what can be done to regain the lost capabilities?
Option 1: Create a 5.56mm "heavy ball" load
The simplest approach to improving the combat potential of 5.56mm weapons is to increase bullet weight. This has been done on a limited scare by special operations forces, which have used Mk262 competition ammo in the mountains of Afghanistan. The 77-grain open tip match bullet reportedly is effective when used against unprotected enemy personnel, but the open-tip design is less capable than a full metal jacket (FMJ) projectile for penetration of barricades, brick walls, vehicles and other "hard" targets.
In the 1960s, a German company developed a "heavy ball" load with a steel-jacketed, 77-grain bullet that would be a viable quick-fix to the problem, since long range trajectory and hard target penetration appear to be better than that of the M855 round. The manufacturer was unable to generate any interest at the time, no doubt because the heavy projectile was incompatible with the slow rifling twist used in M16A1 barrels. However, since it would be stabilized by the faster twist that is used in the M16A2 and M249, it could be worthwhile to either resurrect this loading, or create a FMJ version of the 77-grain Mk262 ammo.
Although it performs well in some circumstances, the 5.56x45mm cartridge has been found wanting in others, and lacks the growth potential necessary to meet these demands. While a heavier bullet would certainly boost the performance of 5.56mm NATO, if a substantial improvement is desired it will be necessary to adopt an entirely new caliber, one that is more capable than the current loading. It would be best if any new cartridge is dimensioned so current and future weapons can be reconfigured to fire it, with minimal expenditure of time and money. This limits cartridge overall length to that of the 5.56x45mm round, but allows some flexibility in regards to case diameter. Rifle modifications should be restricted to replacement of the barrel, bolt, and magazines, while conversion of belt-fed LMGs will necessarily be a bit more involved, requiring changes to the feed tray and top cover in addition to installing a new barrel and bolt.
Option 2: Load a bigger bullet in the 5.56x45mm case
The second easiest way to increase performance is to "neck up" the 5.56x45mm case to accept a 6mm bullet, something that has been done by civilian competition and varmint shooters who wanted more capability than the original round could provide. The result is the "wildcat" 6x45mm cartridge (not to be contused with the 6x45mm XM732 round that was developed in the 1970s), which can be loaded with bullets weighing 80-90 grains, with ogives that allow overall cartridge length to be the same as M855 ball.
To achieve a flat trajectory, and thereby improve long range capability, requires a higher degree of ballistic efficiency than can be provided by the 6x45mm. Since very streamlined bullets tend to have greater length, to load such projectiles into the basic 5.56mm cartridge case will make it necessary to shorten the case slightly. Although the smaller powder capacity will reduce muzzle velocity, the superior projectile shape results in more retained velocity at the target. Case length depends on the diameter and shape of the projectile selected for use, but should be about 41mm with a 6mm bullet, and possibly somewhat shorter if caliber is 6.5mm or larger.
Option 3: Use a bigger bullet and a bigger cartridge case
Recently there was an effort by individuals at the Special Operations Command, in collaboration with an ammunition producer, to create a more potent special purpose cartridge (SPC) for close combat. The 6.8x43mm case has a larger volume than that of the 5.56x45mm, and holds enough propellant to give a 115-grain projectile a respectable velocity. The 6.8mm SPC will definitely hit harder than M855 ball at all engagement distances, but because the bullet has only modest aerodynamic qualities, trajectory and retained velocity are less than optimal. However, the SPC case has been necked down to 6.5mm and 6mm, allowing it to be loaded with projectiles of higher ballistic efficiency, and these smaller-caliber versions would undoubtedly be better general purpose rounds.
With the possible exception of some of the SPC variants, the cartridges covered to this point are not truly adequate for engagements of point targets with the M16A2 rifle or M4 carbine beyond about 500 meters. In 1998, a civilian competition shooter began a quest for a cartridge that could give the M16 family the capability for precision shots out to twice that distance. The end result was a 6.5x38mm round--dubbed the 6.5mm Grendel by the manufacturer (Grendel was a powerful mythological monster)--that can attain good velocities with medium weight bullets of very high ballistic efficiency. When fired from a 20-inch barrel, the 6.5x38mm shoots highly-streamlined bullets of 100-123 grains with a flatter trajectory and less wind drift than 7.62mm M80 Ball ammo, and does so with negligible recoil.
Which is the best cartridge for upgrading the combat capability of 5.56mm infantry weapons depends on just how much improvement is desired. Clearly, a 5.56mm heavy bullet load would be the most economical choice, because no alterations to the weapons are necessary, but expected performance increase is minimal. The 6x45mm and 6x41mm rounds would provide more significant gains, and require little more than a barrel change, since these rounds fit existing bolts, magazines, and metallic links.
The 6.8x43mm and 6.5x38mm are the most expensive alternatives, requiring replacement of bolts, barrels, magazines, as well as the development of new machine gun links, but they are by far the most effective options. The 6.8x43mm cartridge would provide a substantial improvement in close combat capability, which was its stated design purpose. However, the streamlined projectiles fired by the 6.5x38mm round deliver vastly superior all-around performance, combining improved penetration of battlefield obstacles with enhanced capability to "reach out and touch someone" at long distance.
When it was learned in the early 1990s that the Chinese Army was planning to field a new family of small arms, it was widely thought that the new weapons would be chambered for the Russian 5.45x39mm cartridge. To the surprise of experts worldwide, the Chinese instead created a unique 5.8x42mm round that, by any objective standards, must be considered the best assault rifle cartridge currently in service. The U.S. Army should take similarly bold action and adopt a new, more capable rifle cartridge so that Soldiers will be better armed to meet the challenges that they will encounter on the diverse battlefields of the 21st century.
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Velocity(ft/sec)--20.0"barrel Range(meters)
Cartridge / Bullet 0 100 300 500 800 1000
5.56x45mm 62gr 3100 2731 2076 1529 1032 895
5.56x45mm 77gr 2750 2481 1989 1564 1117 971
6x45mm 87gr 2650 2396 1931 1530 1110 971
6x41mm 90gr 2600 2375 1958 1591 1177 1022
6.8x43mm 115gr 2700 2417 1903 1470 1055 929
6.5x38mm 108gr 2700 2497 2117 1774 1345 1142
6.5x38mm 123gr 2600 2426 2098 1797 1410 1211
7.62x51mm 147gr 2700 2473 2051 1676 1238 1063
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Energy(ft-lbs)--20.0"barrel Range(meters)
Cartridge / Bullet 0 100 300 500 800 1000
5.56x45mm 62gr 1323 1027 593 322 146 110
5.56x45mm 77gr 1293 1052 676 418 213 161
6x45mm 87gr 1357 1109 720 452 238 182
6x41mm 90gr 1351 1127 766 506 277 209
6.8x43mm 115gr 1861 1492 925 552 284 220
6.5x38mm 108gr 1748 1495 1075 754 434 313
6.5x38mm 123gr 1846 1607 1202 882 543 400
7.62x51mm 147gr 2379 1995 1373 917 500 368
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Velocity(ft/sec)14.5"barrel Range(meters)
Cartridge / Bullet 0 100 300 500 800 1000
5.56x45mm 62gr 2750 2408 1802 1320 958 848
5.56x45mm 77gr 2500 2245 1782 1396 1038 924
6x45mm 87gr 2500 2254 1806 1428 1061 942
6x41mm 90gr 2450 2232 1830 1483 1115 986
6.8x43mm 115gr 2600 2323 1822 1405 1028 912
6.5x38mm 108gr 2600 2401 2030 1696 1288 1105
6.5x38mm 123gr 2450 2282 1965 1677 1318 1144
7.62x51mm 147gr 2500 2279 1870 1515 1131 995
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Energy--14.5" Barrel Range(meters)
Cartridge / Bullet 0 100 300 500 800 1000
5.56x45mm 62gr 1041 799 447 240 126 99
5.56x45mm 77gr 1069 862 543 333 184 146
6x45mm 87gr 1207 982 630 394 217 171
6x41mm 90gr 1199 996 670 440 249 194
6.8x43mm 115gr 1726 1378 847 504 270 212
6.5x38mm 108gr 1621 1383 988 690 398 293
6.5x38mm 123gr 1639 1422 1054 768 474 357
7.62x51mm 147gr 2040 1694 1141 749 418 323
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20.0"barrel Deflection@1000m
Cartridge / Bullet 10 mi/hr crosswind
5.56x45mm 62gr 209 in
5.56x45mm 77gr 174 in
6x45mm 87gr 173 in
6x41mm 90gr 154 in
6.8x43mm 115gr 191 in
6.5x38mm 108gr 124 in
6.5x38mm 123gr 109 in
7.62x51mm 147gr 145 in
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20.0"barrel Trajectory
Cartridge / Bullet when fired to 1000m
5.56x45mm 62gr 265 in
5.56x45mm 77gr 242 in
6x45mm 87gr 250 in
6x41mm 90gr 228 in
6.8x43mm 115gr 272 in
6.5x38mm 108gr 181 in
6.5x38mm 123gr 172 in
7.62x51mm 147gr 194 in
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14.5" barrel&1000m
Cartridge / Bullet 10 mi/hr crosswind
5.56x45mm 62gr 230 in
5.56x45mm 77gr 189 in
6x45mm 87gr 182 in
6x41mm 90gr 163 in
6.8x43mm 115gr 197 in
6.5x38mm 108gr 131 in
6.5x38mm 123gr 118 in
7.62x51mm 147gr 161 in
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14.5" Barrel Trajectory
Cartridge / Bullet when fired to 1000m
5.56x45mm 62gr 332 in
5.56x45mm 77gr 293 in
6x45mm 87gr 281 in
6x41mm 90gr 258 in
6.8x43mm 115gr 293 in
6.5x38mm 108gr 197 in
6.5x38mm 123gr 189 in
7.62x51mm 147gr 249 in
Stanley C. Crist served in the 3rd Battalion, 185th Armor, and has worked as a small arms ammunition consultant. He is the author of numerous articles on small arms testing and evaluation, and his work has appeared in Infantry, Armor, and Special Weapons for Military and Police magazines.
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