Editing M16 rifle (section)

===Terminal ballistics===
The 5.56×45mm cartridge had several advantages over the 7.62×51mm NATO round used in the M14 rifle. It enabled each soldier to carry more ammunition and was easier to control during automatic or burst fire.{{sfnp|Crawford|2003|p=85}} The 5.56×45mm NATO cartridge can also produce massive wounding effects when the bullet impacts at high speed and yaws ("tumbles") in tissue leading to fragmentation and rapid transfer of energy.{{sfnmp|1a1=Courtney|1a2=Courtney|1y=2008|1p=4|2a1=McNab|2y=2002|2pp=108–109|3a1=Rose|3y=2008|3pp=375–376}}

{| class="wikitable" style="margin: 1em auto; text-align:center;"
|- valign="top"
! rowspan="2" |Rifle
! rowspan="2" |Caliber
! rowspan="2" |Cartridge
! colspan="7" |Penetration
|-
! <small>[[Ballistic gelatin]] <br />@ 10 meters</small>
! <small>[[Sandbag]]s <br />@ 100 meters</small>
! <small>3/4" pine boards <br />@ 100 meters</small>
! <small>Concrete building block <br />(one center rib)</small>
! <small>[[Steel helmet]]</small>
! <small>1.9mm steel <br />(14 gauge) <br />@ 100 meters</small>
! <small>4mm steel <br />(8 gauge) <br />+ layers of <br />Kevlar-29</small>
|-
!M16
|[[5.56×45mm|5.56×45&nbsp;mm]]
|M193
|<small>≈{{convert|14|in|cm|abbr=on}} <br />(bullet fragments <br />into smaller pieces){{sfnmp|1a1=Fackler|1y=2007|1p=1|2a1=Fackler|2y=2010|2p=3}}</small>
|<small>{{convert|4|in|cm|abbr=on}} <br />(complete bullet <br />disintegration){{sfnp|Defense Technical Information Center (DTIC)|1962|p=73}}</small>
|<small>8 boards <br />(bullet tumbled){{sfnp|Defense Technical Information Center (DTIC)|1962|p=73}}</small>
|<small>one side to 200&nbsp;m{{sfnp|Defense Technical Information Center (DTIC)|1962|p=73}}</small>
|<small>both sides to 300&nbsp;m <br />one side to 500&nbsp;m{{sfnp|Defense Technical Information Center (DTIC)|1962|p=73}}</small>
|<small>2 layers{{sfnp|Defense Technical Information Center (DTIC)|1962|p=73}}</small>
|<small>31 layers of Kevlar{{sfnp|Slepyan|Ayzenberg-Stepanenko|1998|pp=7}}</small>
|}

{{multiple image
| caption_align = center
| header_align = center
| align = right
| direction = vertical
| width = 300
| header = [[Wound ballistics|Wound profiles]] in ballistic gelatin <br /><small>Note: images are not to same scale</small>
| image1 = M16 5.56x45mm wound ballistics.gif
| alt1 = M16 5.56×45mm wound ballistics
| caption1 = M16 M193 5.56×45&nbsp;mm
| image2 = M16A2 M855 5.56X45mm NATO wound ballistics.gif
| alt2 = M16A2 M855 5.56×45mm wound ballistics
| caption2 = M16A2 SS109/M855 5.56×45&nbsp;mm NATO
}}
The original ammunition for the M16 was the 55-grain M193 cartridge. When fired from a {{cvt|20|in|mm}} barrel at ranges of up to {{convert|100|m|ft|sigfig=1|order=flip}}, the thin-jacketed lead-cored round traveled fast enough (above {{cvt|2900|ft/s|m/s}}) that the force of striking a human body would cause the round to yaw (or tumble) and fragment into about a dozen pieces of various sizes thus created wounds that were out of proportion to its caliber.{{sfnmp|1a1=Fackler|1y=2007|1p=1|2a1=Fackler|2y=2010|2p=3}} These wounds were so devastating that many considered the M16 to be an inhumane weapon.{{sfnmp|1a1=Hogg|1a2=Weeks|1y=1985|1pp=195-196|2a1=Prokosch|2y=1995|2p=1}} {{NoteTag|Those who consider the M16 inhumane include; the International Committee of the Red Cross, Austria, Argentina, Belgium, Bolivia, Bulgaria, Burundi, Cambodia, Cyprus, Germany, Ireland, Latvia, Lithuania, Luxembourg, Mauritius, Mexico, Romania, Samoa, Slovenia, Sweden, Switzerland, etc.{{sfnp|Parks|2010|pp=2}} }}As the 5.56&nbsp;mm round's velocity decreases, so does the number of fragments that it produces.{{sfnp|Ehrhart|2009|pp=25-26}} The 5.56&nbsp;mm round does not normally fragment at distances beyond 200 meters or at velocities below 2500&nbsp;ft/s, and its lethality becomes largely dependent on shot placement.{{sfnmp|1a1=Ehrhart|1y=2009|1pp=26-27|2a1=Fackler|2y=2007|2p=1}}

With the development of the M16A2, the new 62-grain M855 cartridge was adopted in 1983. The heavier bullet had more energy and was made with a steel core to penetrate Soviet [[body armor]]. However, this caused less fragmentation on impact and reduced effects against targets without armor, both of which lessened kinetic energy transfer and wounding ability.{{sfnp|''The New York Times, At War Blog'', November 12, 2009}} Some soldiers and Marines coped with this through training, with requirements to shoot vital areas three times to guarantee killing the target.{{sfnp|''The New York Times, At War Blog'', November 3, 2009}}

However, there have been repeated and consistent reports of the M855's inability to wound effectively (i.e., fragment) when fired from the short barreled M4 carbine (even at close ranges).{{sfnp|Ehrhart|2009|pp=27-28}} The M4's 14.5-in. barrel length reduces muzzle velocity to about 2900&nbsp;ft/s.{{sfnp|Colt, ''M4 5.56mm Carbine''|2003}} This reduced wounding ability is one reason that, despite the Army's transition to short-barrel M4s, the Marine Corps has decided to continue using the M16A4 with its 20-inch barrel as the 5.56×45mm M855 is largely dependent upon high velocity in order to wound effectively.{{sfnp|Ehrhart|2009|pp=27-28}}

In 2003, the U.S. Army contended that the lack of lethality of the 5.56×45mm was more a matter of perception than fact.{{sfnmp|1a1=Army Infantry Center|1y=2003|1p=8|2a1=Dean|2a2=LaFontaine|2y=2008|2p=3}} With good shot placement to the head and chest, the target was usually defeated without issue.{{sfnmp|1a1=Army Infantry Center|1y=2003|1p=8|2a1=Arvidsson|2y=2012|2p=769}} The majority of failures were the result of hitting the target in non-vital areas such as extremities.{{sfnp|Army Infantry Center|2003|p=8}} However, a minority of failures occurred in spite of multiple hits to the chest.{{sfnp|Army Infantry Center|2003|p=9}} In 2006, a study found that 20% of soldiers using the M4 carbine wanted more lethality or stopping power.{{sfnp|Rose|2008|pp=403–405}} In June 2010, the U.S. Army announced it began shipping its new 5.56&nbsp;mm, lead-free, M855A1 Enhanced Performance Round to active combat zones.{{sfnp|Woods|2010|p=35}} This upgrade is designed to maximize performance of the 5.56×45mm round, to extend range, improve accuracy, increase penetration and to consistently fragment in soft-tissue when fired from not only standard length M16s, but also the short-barreled M4 carbines.{{sfnp|Woods|2010|p=35}}{{sfnp|''SCAS Hearings''|2010}} The U.S. Army has been impressed with the new M855A1 EPR round.{{sfnp|Slowik|2012|p=1}} A 7.62 NATO M80A1 EPR variant was also developed.{{sfnp|''The Firearm Blog'', 16 June 2016}}{{sfnp|''The Firearm Blog'', 23 July 2016}}