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4/1/2020 4:14:10 PM
4/1/2020 6:58:51 AM
Posted: 1/5/2005 6:09:16 AM EDT
[Last Edit: 1/5/2005 6:10:49 AM EDT by Autobahndriver]
Infantry Magazine Article Text Link

Small arms ammunition for the 21st century: high performance alternatives to the 5.56 NATO round
Infantry 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It has been four decades since the 7.62mm NATO round began to be superseded as the ammunition of choice for U.S. combat rifles when the 5.56x45mm M193 cartridge--and the M16A1 rifle that fired it proved better stilled to the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.
_______________
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
_________________
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
____________________
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
__________________
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
__________________
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
____________________
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
______________________
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
__________________
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.

COPYRIGHT 2004 U.S. Army Infantry School
COPYRIGHT 2004 Gale Group
Link Posted: 1/8/2005 7:36:21 AM EDT
thanks good read.  5.56 was good for vietnam but needs to be upgraded.  you hit wire and they ricochet.  i vote for 7.62x51.  makes sense for everyone to have the same ammo.  the M240B, gift from the gods.
Link Posted: 1/12/2005 5:55:55 AM EDT
Look at what two rounds are carrying the highest velocity when you get to 100meters then 300meters - shows how little muzzle velocity tells you.

Velocity(ft/sec)14.5"barrel Range(meters)

Cartridge / Bullet      0     100    300   500   800 1000

5.56x45mm 77gr   2500 2245 1782 1396 1038 924
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
Link Posted: 1/12/2005 6:00:59 PM EDT
light bullets ricochet too easily.  those charges must be hot to get those velocities out of a 14.5 barrel.
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