Lethality of 5.56mm

Being a military armorer, I get a lot of discussion about what round is better than the next.  The 9mm vs .45 debate comes up a lot.  I also hear a lot of misconceptions around military ammo, specifically the 5.56x45mm.  My thought process is the best round is the one that you have, that works.  I'm issued a variety of calibers, and have a lot of experience with unusual (for regular troops) military ammo.  In this post I want to go over some of the 5.56mm options and lethality, and what is being done to close those gaps.



The M16 platform is our old war-horse with its 20" barrel, and it is still in use in a wide number of units.  The Army is looking to expand M4 issue to more units in the coming years.  I myself have only been issued an M16 at one unit, and that was short lived.  I've almost exclusively trained with M4A1's and Close Quarter Battle Rifle's (Mk18).  The significant difference being the 14.5" and 10.3" barrel length respectively.  When taking a round designed for a 20" barrel, and placing it through such a reduced barrel, our lethality potential also gets cut with reduced muzzle velocities.

CQBR / Mk18 Upper

Back in the early M16 days, we were not in standard with the NATO SS109 round.  We were using the 55-grain M193 round.  It was extremely effective on fleshy targets such as VC Guerrillas.  So much so that it was being called inhumane.  What made the round so effective was the high muzzle velocity (3,100fps) and the way the bullet traveled.  The round wobbled slightly, and on impact, it almost immediatly would yaw (tumble).  The yaw combined with a high velocity would cause the bullet to fragment violently in the target, causing severe trauma.

Currently we are using the NATO 62-grain M855 'green-tip' steel penetrator and our barrels have a faster twist for the heavier bullet, 1:7 right-hand from the previous 1:12.  Where we get into trouble is that round was made for the M16 20" barrel, not our M4's and certainly not our CQBR.  The new round has a lot of potential for 'through-and-through' hits where the bullet does not yaw/fragment, and passes through the target inflicting less injury.  Many argue the round as ineffective and studies agree.  Many reported having to hit hostiles multiple times to achieve a drop.  I can argue shot placement at this point, many units will not train to make head-shots.  I can tell you that if you take a guy pumped full of adrenaline and trying to kill you, that you can hit him in the lungs, heart, liver or spleen, and it will feel like eternity before he is face down on the ground.  The only 'instant' party-stopper is a central nervous system hit, brain or spine.


Studies are showing that the M855 being fired from the M4's have the highest potential for lethality at 50 meters and CQBR's at 30 meters.  That's closer than comfort but common engagements were in that range window in Iraq, but far less so in Afghanistan.  The M855 is where a lot of the controversy over the ineffectiveness of 5.56mm comes from in my mind.  The round has shown a lack of performance from the shorter M4/CQBR, producing a lot of through-and-through hits.  We were ordering the Mk262 round, which is a heavier 77-grain open-tip boat-tailed match round to use for combat application.  It was meant for use in the Mk12 Special Purpose Rifle (Sniper), but we and many other units found that it worked extremely well in our M4's and CQBR's for both close and long range.  The other option available was to use Reduced Ricochet Low Penetration (RRLP) Frangible rounds.  Those proved effective close-in but not at range.

As of 2010, the Army has begun production of a new round, dubbed the M855A1 Enhanced Performance Round.  This new round is a lead-free penetrator backed by a copper slug that does not rely on yaw for its performance and is tailor made for the shorter M4/CQBR barrels.  The round is to provide increased accuracy, lethality, and barrier penetration (all in part a function of higher muzzle velocity) while also reducing muzzle flash.  According to the testing done, when engaging against a windshield for instance, point of aim will be point of impact behind the glass.  The penetrator will travel high coming into the vehicle, but the copper slug would continue straight.  That used to be a major deficiency of the standard M855.  The release info shows a lot of interesting data from their testing. 

I think we may have finally closed the door on 5.56mm round troubles, hopefully as the information gets out and real-world engagement results from M855A1 start showing up people will get more behind the caliber.  I wonder if the BATF will make an exclusion for this round like they did the M855?  Despite the newer M855A1 hitting the streets, the quest for a larger caliber still rages behind the scenes, so we very well may eventually move away from 5.56mm in the future, and I agree the smart thing to do would be to do a round of research on an optimal cartridge before we worry about new platforms to shoot the same old round.