This article was first published on retired Maj Will Rodriguez’ GruntsandCo. Here. Thank you for letting us repost this~Mike Editor
M855A1 (L), Mk 318 (R)

The House Armed Services Committee asked the Pentagon in late April why the Army and the Marines use different primary ammunition types in their most common small arms caliber 5.56mm.  It’s a curious contradiction since the Army and Marines are fighting the same enemy in the same regions of the world.  Now that the worldwide operational tempo has slackened a tad, it makes sense to look for some significant cost savings and simplification of supply to be realized by going to a common munition.  The Secretary of Defense has until March next year to explain meanwhile, testing is ongoing.

This question by Congress caused a virtual avalanche of commentary in the blogosphere with an overwhelming majority of it slanted to the Marine Corps benefit assuming it made a better choice and trying to create a fight between branches where none is necessary.  Let’s try and get past the BFF branch perspective and come to understand how the current situation arose and objectively assess the two rounds.


For most of the last three decades the Army and Marines primary 5.56 round has been M855 or “green tip” such named because of its green painted tip to differentiate it from other ammunition.  M855 was originally created for the M249 SAW by our European allies and is called SS109.  It was type classified as M855 for US use in the M16A2 rifle in the mid-80’s.  M855/SS109 was developed in the 1970’s with the desire to create a round that would penetrate body armor and helmets typically equipping Soviet forces of the period.

M855’s armor penetration is provided by a small steel penetrator placed in the bullet during production.   Yaw provided M855’s anti-personnel effect.  Yaw is the tendency for a bullet’s tail to wobble around its direction of flight axis.  Imagine a top wobbling as it spins but traveling bottom first towards its target.  Anyone with top spinning experience knows wobbling isn’t really predictable (or much) but increases as the top slows down.  Transfer this to M855 lethality, we counted on M855 striking at an angle produced from yaw (unpredictable yaw) causing it to tumble upon striking a target creating horrific damage.  M855 production imperfections (one can’t place that steel penetrator in every round precisely at the same spot impacting center of gravity) help create yaw but not predictably from round to round.  Complaints starting in Somalia of “through and through” wounds (M855 traveled through the target relatively cleanly causing a minimum if damage) to the enemy especially at close range grew during our early years in Afghanistan and Iraq.

Further, it was noted that M855’s soft lead composition had a tendency to malform when hitting the high angle of many windshields and deflect vs. going through the glass.  This was an especially important issue when confronting vehicle borne IED’s.  Special Operations Forces and the Marines looked for munitions with more lethal effect, both adopting Mk262 at about four times the cost of M855.  The Marines migrated to Mk318 in ’09.  The Army already funded to create a “green round” decided to take a more surreptitious route to develop a more lethal round that also answered the identified shortcomings eventually resulting in M855A1.


Today, the Army primarily uses the M855A1 round while the Marines use Mk318 Mod 0 supplemented with M855.  M855A1 is the innovative result of the Army’s decade’s long effort to field a non-lead round to satisfy environmental concerns.  M885A1 is an exceptionally lethal sub 2 MOA (less than 2” spread between rounds at 100 yrds.)  M855A1 is similar to M855 “green tip” as the bullet weighs 62 grains, overall round weight is the same and is copper jacketed (except for the very tip).  The tip of the bullet is where the expansive changes start to become apparent. M855A1’s tip is bronze-colored because of the anti-corrosive coating on its hardened steel penetrator.  The steel tip is bonded to a copper slug behind the tip.  Propellant is temperature stabilized and has additives minimizing muzzle flash and copper fouling in the barrel.  The propellant creates a 13% increase in chamber pressure but ballistically is a near match with M855.

More importantly, the capabilities of M855A1 are significantly different than M855.  The round is barrier blind meaning it penetrates moderate barriers and continues on its path predictably.  M855A1 performance against soft tissue is classified but based on conversations I’ve had with ARDEC representatives at Ft. Benning during a conference they are much better than M855 and not yaw dependent.  Based on Liberty Ammunition’s T3 round upon which the M855A1 is based and observations about the steel penetrator specifically ricocheting farther than M855 I would speculate the round fragments after striking its target, causing extensive damage.  Where M855A1 really shines is in penetration.  It penetrates 3/8” of steel exceeding M80 7.62mm, the average medium machine gun round fielded to our forces.   M855A1 can penetrate some types of body armor and even cinder block and concrete to a degree maintaining enough power to wound the enemy using it for cover.  Taken as a whole this is far and above any 5.56 round generally fielded.

It’s important to digress and explore the “green round” story at this point.  As silly as it sounds, environmentalists have been successful stopping and even ending certain military training.  The Navy’s use of sonar on the Pacific coast, the loss of the only naval gunnery, aviation live fire and ground operations training on Puerto Rico’s Vieques Island and the limits placed on training areas at Ft Bragg to save the red-cockaded woodpecker have all been environmental victories that minimized or eliminated necessary military training.

The Army has serious concerns about lead from ammunition leeching into the environment and giving environmentalists “ammunition”.  This impacts training areas not only in the middle of nowhere but those in close proximity to towns or very large environmentally super sensitive parts of the country where portions of its over 500 thousand man Guard and Reserve forces train.  Sadly it’s important to address the “environment” issue early on because so much of the knee jerk negative reaction to the M855A1 stems from it.  It often drowns out the round’s significant capabilities and the ingenious way certain Army communities “used” funding dedicated for green round development to create lethality advancements and satisfy the environmental requirement.

Mk318 Mod 0

The Marines selected Mk318 Mod 0 to supplement M855 (Marines still use M855) primarily because of a delay in perfecting M855A1 in 2009.  The bullet design is an Open Tip Match Rear Penetrator (OTMRP).  The front of the bullet is open tipped (followed by a lead core and the rear half is brass).  When the bullet hits a surface, the front half of the bullet collapses breaking the glass surface.  The rest of the bullet follows through the hole created hitting the target.  It is also considered “barrier blind” against light wall materials and windshields.  The round is also rated at 2 MOA level of accuracy and is sometimes called the Mk 318 Special Operations Science and Technology (SOST) round because of its original development in the Special Operations community.

M855A1 criticism in the media, emotion and thinking backwards

There have been a multitude of articles written where hyperbole and quasi emotional arguments have replaced objective analysis.  That approach by respected publications like Stars and Stripes has had an exponential effect on the argument because they are often repeated in other media sources parroting a poorly written article instead of conducting independent reporting.  Heck, the Army and Marine Times used the same slanted story word for word.  The debate even becomes more slanted when the overwhelming majority of the media report only the counter M855A1 perspective and do not conduct the same level of analysis on Mk318.

Weak techniques and arguments disparaging M855A1

Troops have criticized M855 because it “didn’t penetrate windshields predictably and did not consistently incapacitate the enemy”.  TRUE, but we aren’t comparing M855 to Mk318!  A common weakness of many of the afore mentioned articles is they spend more time discussing M855 than M855A1.  That makes no sense since we are comparing M855A1 which doesn’t have a problem penetrating windshields (and much more) and very predictably incapacitates the enemy.

“The Marines didn’t adopt M855A1 in ’09 because it had accuracy problems”.  True and the Marines made an arguably good decision to field Mk318 which was four times cheaper than Mk262 at a time when the Army had yet to provide a round after years of development.  The problem is in these articles is they almost all fail to mention the Army fixed the problem a months later and has been issuing the M855A1 since.  Isn’t that relevant or is leaving an incorrect impression in the mind of the reader more sensational?

One of the silliest points I have seen mentioned for the Marines not wanting to switch to M855A1 is because some rifle ranges would have to be retrofitted  due to M855A1’s increased penetration and ricochet effects.  Said another way, we don’t want this new round because it’s more lethal!  When we develop a grenade more effective than the current 40mm or hand grenade will we not adopt it because training ranges aren’t built for it?

“M855A1 is a green round.”  Yes, M855A1 is environmentally friendlier than other ammunition but why is that bad?  Though mentioning this boogey man assists in avoiding actually talking about M855A1’s actual performance.  Major Glenn Dean wrote a fascinating book on the backstory of the development of the M855A1 round.  “In Search of Lethality: Green Ammo and the M855A1 Enhanced Performance Round” tells the story of how the Army’s acquisition, Infantry and Special Forces communities came together and recognized the need for a round with increased lethality and used funding for a green round to develop not only a green round but one with much greater lethality.

Almost all stories written about the M855A1 fail to address this largely undiscovered history.  I can’t comment if the lack of reporting is from a lack of researching effort or a desire to preserve unnecessary sensationalism to camouflage a lack of analysis.  It might be attributed to what Major Dean says was a conscious decision by the Army developers to not communicate M855A1’s dual requirement strategy in an effort to avoid concern we weren’t killing the enemy humanely enough.

Some writers have created a controversy over some official Army slides touting M855A1 as having  “match” like accuracy.  It was a bad choice of words to communicate the uniformity of bullet production but no worse than the Marine Corps use of the word match in describing Mk318 as Open Tip Match Rear Penetrator.  This use of the word “match” did not raise the same level of concern for orthodoxy.  In the end both rounds are rated at sub 2 MOA.

Most importantly, none of these often mentioned “issues” address any concrete lack of performance in the M855A1 round.

The best arguments against M855A1 revolve around allegations of excessively fouling and by three concerns raised by Col. Michael Manning, the program manager for Infantry Weapons Systems at Marine Corps Systems Command in Quantico, Virginia who blamed the M855A1’s high chamber pressure and exposed steel tip for eroding barrels, cracking bolts and chewing up a feed-ramps.

The source of the excessive fouling allegation is from manufacturers who submitted their weapons into the Individual Carbine Competition, a competition to select a replacement for the current M4.  The Army concluded that no new candidate met the desired and admittedly high desired performance standards.  Manufacturers were surprised at the outset of the competition by the requirement to use M855A1 when they had expected M855.  Fouling became a primary excuse submitted by manufacturers for their weapons not passing the very high Army standards.  Col. Paul Hill the Army’s project manager for ammunition said, “I had heard that anecdotal information that the M855A1 did create more fouling,” But when he arranged an extensive series of tests, Hill said, “we found…. there was no significant difference in fouling between the M855 [the old round] and the M855A1.”

The higher chamber pressure of M855A1 is connected to wearing out barrels and cracking the locking lugs on bolt faces.  Wearing out of barrels is a valid observation although it typically happens after the 10k rounds mark which is when barrels are supposed to be replaced anyway.  The occasional cracked bolt is a valid observation but as Nathaniel F. from relayed to me, “the old M855 would do that if you fired enough of it…  M855A1 stresses the bolt lugs of an M4 out much, much less still than alternative rounds like 6.8mm SPC or 6.5 Grendel.”

M855A1 is indeed tearing up uppers.  The steel tip brings upper life down from 40k to 20k, a significant cost but the same articles that mention this shortcoming do not share a new magazine follower and magazine in development fixes this problem and early testing improves reliability 300%.  This is a curious and important lapse in objective reporting.

It is worthwhile to note that Col. Manning’s concerns were based on a 2006 Special Forces torture test.  Part of the test consisted of firing 3000 rounds on full automatic.  The Naval Surface Warfare Center does small arms development for the Naval Special Warfare community notes that the bolt failures noted by Com Manning are pretty normal for hard firing regimens at 3000-6000 rounds (slide 44).  Is the program manager for Infantry Weapons Systems at Marine Corps Systems Command in Quantico unaware?  In sharp contrast to Marine concerns, Brig. Gen. Paul Ostrowski chief of Program Executive Office (PEO) Soldier said of the new round, “we have experienced absolutely zero issues with the M855A1 in combat.”

One facet completely absent from much of the main stream discussion about the two rounds is body armor.  We train to shoot center mass based on the assumption that the enemy is unarmored.  We cannot continue to follow the age old trend of fighting the next war like the last one where our insurgent enemy has largely been unarmored especially in light of the growing use of body armor.  While 2nd, 3rd world militaries and most insurgents (those who don’t get captured vests) don’t field modern plate based body armor and China isn’t really issuing all their troops body armor that is changing.  Russia is catching up and fielding effective body armor but are relative newcomers to modern ceramic armor manufacturing techniques.  We should also remember that even the best plate based armor is held together by soft armor.  In this area, M855A1 has superior penetration performance.

To date the debate about M885A1 and M318 has been highly slanted.  We would hope promised Marine testing will be done in a scientifically objective manner.  The Army’s significantly higher ammo purchase requirements and the accompanying savings should also be accounted for in purchasing any ammo in bulk.

From the previous discussion its obvious M855A1 works well against soft tissue and soft barriers e.g. windshields (just like Mk318) AND with increased capability against cinderblock, concrete and steel.  The reason the Marines continue to field the lower performing M855.  Not only is M855A1 effective against those not wearing body armor, it’s more effective against the enemy using cover and better equipped enemy wearing lower quality body armor.

Whatever round is selected, the bottom line is superior barrier penetration AND better soft tissue capability in the SAME round is a significant advantage.

Additional Research:

Liberty Ammunition T3 video through windshield.  This is a civilian round by the patent holder of the M855A1 technology.  It’s an open source perspective on effectiveness and lethality using ballistic gelatin.  It’s not M855A1 but it’s the closest unclassified info you’ll find.

The only actual objective M855A1 testing

Army Sniper Anecdote -“There is something to be said for mass and energy M855 is only 62 grs M80 is 147gr. At 300 meters M855A1 penetrated a steel target that the M80 ball could not, making it a better penetrator than a bullet with more than twice its mass and energy.”  – SFC T

Well I am an army sniper deployed with 3rd group special forces we use the m855a1 and were putting 25 out of 30 rounds in an 1/4 in steel iron maiden at 750 meters we use it in high heat of Afghanistan at 8000 feet and in 34 mile per hour full value winds I love the round it shoots straighter than the 77 grain LR rounds it&#039s better than green tip only issue is it penetrates to well with little to no expansion but it will penetrate glass like paper and it goes through a land rovers quarter panel and engine block pretty easy for those ISAF guys that have strict roe it&#039s great you&#039ll stop a moving vehicle quiet easy it just takes better shot placement to get your enemy down because it pokes small holes but suicide vests Kevlar even our issued plates don&#039t stand up against these rounds I like lead because it puts the enemy down easier with half assed shot placement in a fire fight that&#039s how it&#039s gonna be but I love this round maybe we get better ammo who knows but it&#039s pretty awesome stuff push out to your weapons max effective with thirty rounds see if you don&#039t like it shoot at iron maidens shoot things made of metal you&#039ll find out too that it&#039s a very dangerous round just be aware where you shoot cause it goes through every thing. – Anthony Kirkpatrick

Magazine replacement slide 5

M855A1 presentation

M855A1 History by Plaster

Acknowledgement: I’d also like to acknowledge Nathanial at the firearmsblog who provided some unique and outstanding insight on the issues I wrote of.  The article would not have been as well documented without his input.  I encourage a visit to the blog for knowledgeable and objective assessments.

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About The Author

Will Rodriguez is a 20+ year former Infantry officer with experience in both light and mechanized units as well as armor. His last assignment was serving in the Infantry school's battle lab doing DOTMLPF (doctrine, organization, training, materiel, leadership and education, personnel and facilities) assessment on weapon systems, equipment) assessment on weapons systems, equipment and technology to equip the Infantry for the next 10-20 years. Will also is the senior editor for a website dedicated to issues of interest to the Infantrymen and those that support them. Will is a frequent contributor to Spotter up as well as an assistant editor. His work has also been published in,, the Loadout Room and Infantry Magazine. He is also a firearms instructor and holds a masters in Counseling and Leader Development.

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