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Pr
epared for Members and Committees of Congress
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The M-4 carbine is the Army’s primary individual combat weapon for infantry units. The M-4
uses a direct gas impingement system that blows carbon from the fired cartridge back into the
weapon’s receiver, which can lead to weapon malfunctions. The U.S. Special Operations
Command (USSOCOM) is replacing its M-4s with the Special Operations Combat Assault Rifle
(SCAR). It is a modular weapon with a short-stroke piston system which eliminates carbon blow
back that theoretically improves reliability. Some have questioned why the Army has not adopted
the SCAR or another similarly designed weapon. A series of studies and tests of the M-4 and
potential competitors have added to this debate, and the Army has taken steps to begin evaluating
other weapons in late 2009 to replace the M-4. This report will be updated as events warrant.
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Background ..................................................................................................................................... 1
Concerns with M-4 Reliability and Lethality.................................................................................. 1
Center for Naval Analyses (CNA) Study on Small Arms in Combat........................................ 1
Special Forces Opts to Replace the M-4 ......................................................................................... 2
Army’s Asymmetric Warfare Group and the H&K-416.................................................................. 3
M-4 Reliability Testing.................................................................................................................... 3
Congressionally Requested M-4 Test........................................................................................ 3
Congressional Action ...................................................................................................................... 4
Army Looks for a Replacement for the M-4 ................................................................................... 4
Potential Issues for Congress........................................................................................................... 5
Additional Reliability and Lethality Testing ............................................................................. 5
USSOCOM Implications of Replacing M-4s............................................................................ 5
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Author Contact Information ............................................................................................................ 5
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In the mid-1990s, the Army began fielding the M-4 carbine, a lighter, more compact version of
the Vietnam-era M-16 rifle. Both M-16 and M-4 carbines are 5.56 mm caliber weapons and are
primarily manufactured by Colt Defense LLC, Hartford, CT. Army officials are said to be
satisfied with the M-16 family of weapons, suggesting that the M-16 is “simply too expensive to
replace with anything less than a significant leap in technology.”1 The Army’s “leap ahead”
program to replace the M-16 family of weapons—the Objective Individual Combat Weapon
(OICW) program—began in 1994, and one weapon evaluated in that program, Heckler & Koch’s
XM-8 assault rifle, was considered by some as the M-16’s/M-4’s replacement. As late as 2005,
the XM-8 was reportedly close to being officially approved as the Army’s new assault rifle, but
alleged acquisition and bureaucratic conflicts compelled the Army to cancel the XM-8 in October
2005. The Army plans to continue its procurement of M-16s and M-4s for “years to come,” while
some in Congress have called for an “open competition” to choose a successor to the M-16 and
M-4 assault rifles.2
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Reports suggest that soldiers have expressed concerns regarding the reliability and lethality of the
M-4.3 Reliability can be described as “the probability that an item can perform its intended
function for a specified interval under stated conditions” and lethality as “the killing or stopping
power of a bullet when fired from a weapon.”4
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In December 2006, the Center for Naval Analyses (CNA) published a survey and study at the
request of the Army’s Project Manager-Soldier Weapons of 2,600 soldiers who had returned from
Iraq and Afghanistan and who had engaged in a firefight using a variety of small arms. Some of
the M-4-specific observations were as follows:
• Over 50% of soldiers using the M-4 and M-16 reported that they never
experienced a stoppage [malfunction] while in theater, to include during training
firing of the weapons (p. 2).
• Frequency of disassembled cleaning had no effect on the occurrences of
stoppages. Variations in lubrication practices, such as the type of lubrication used
1 Matthew Cox, “Better Than M4, But You Can’t Have One,” Army Times, March 1, 2007, and “Competition Sought
for New Army Rifle,” Army Times, April 27, 2007.
2 Ibid.
3 Ibid.
4 Shawn T. Jenkins and Douglas S. Lowrey, “A Comparative Small Analysis of Current and Planned Small Arms
Weapon Systems,” MBA Professional Report, Naval Postgraduate School, Monterey, CA, December 2004, pp. 29-31.
5 Information in this section is taken from Center for Naval Analyses (CNA) Study: “Soldier Perspectives on Small
Arms in Combat,” December 2006. CNA is a federally-funded research and development center (FFRDC) for the
Department of the Navy.
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and the amount of lubrication applied, also had little effect on stoppages. Using a
dry lubricant decreased reports for stoppages only for M-4 users (p. 3).
• Of soldiers surveyed who used the M-4, 89% reported being satisfied with their
weapon (p. 11).
• Of M-4 users, 20% recommended a larger bullet for the M-4 to increase lethality
(p. 30).
• Regarding M-16s and M-4s,many soldiers and experts in theater commented on
the limited ability to effectively stop targets, saying that those personnel targets
who were shot multiple times were still able to continue fighting (p. 29).
Although M-4 critics cite this report as evidence of unsuitability of the M-4, it might also be
interpreted as a favorable report on the M-4’s overall reliability and acceptance by soldiers. The
“larger bullet” recommendation for lethality purposes may, in fact, be a valid recommendation
based on observations from Iraq and Afghanistan, but the “bigger bullet debate” has been a source
of contention for many small arms experts ever since the Army adopted the 5.56 mm M-16 during
Vietnam in lieu of the 7.62 mm M-14 rifle.
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In 2001, the U.S. Special Operations Command (USSOCOM) was said to have documented M-4
reliability problems in an official report, noting that the M-4 suffered from an “obsolete operating
system” and recommending the redesign of the current gas system.7 The USSOCOM report
allegedly described the M-4’s shortened barrel and gas tube as a “fundamentally flawed”design,
which contributed to failures extracting and ejecting spent cartridges during firing. In recognition
of these deficiencies, the 1st Special Forces Operational Detachment-Delta, also referred to as
“Delta Force,”reportedly began working with German arms manufacturer Heckler & Koch to
replace the M-4’s gas system with a piston operating system to improve reliability and increase
parts life. In 2004, Delta reportedly replaced their M-4s with the HK-416—a weapon that
combines the operating characteristics of the M-4 with the piston operating system.8
In early 2003, USSOCOM officials initiated efforts to identify potential new combat rifle
capabilities.9 From May through August 2004, USSOCOM evaluated 12 weapons from nine
different manufacturers.10 In November 2004, USSOCOM awarded a contract to FNH USA11 to
develop the Special Operations Combat Assault Rifle (SCAR).12 The SCAR will come in two
variants—the heavy 7.62 mm SCAR-H and the light 5.56 mm SCAR-L. 13 Each variant will
6 For additional information on U.S. Special Forces, see CRS Report RS21048, U.S. Special Operations Forces (SOF):
Background and Issues for Congress, by Andrew Feickert.
7 Information in this section is from Matthew Cox, “Better Than M4, But You Can’t have One,” Army Times, March 1,
2007.
8 Matthew Cox and Kris Osborn, “M4,In Their Sights,” Defense News, February 25, 2008.
9 Scott R. Gourley, “Soldier Armed: Special Operations Forces Combat Assault Rifles,” Association of the U.S. Army
(AUSA) Army Magazine, May 1, 2006.
10 “US SOCOM Awards Contract for SCAR Development,” Jane’s International Defense Review, January 2008, p. 26.
11 FNH USA is the U.S.-based sales and marketing entity for the Belgium-based FN Herstal S.A.
12 Scott R. Gourley, “SCAR Evaluation Nears Conclusion,” Jane’s Defence Weekly, March 19, 2009, p. 12.
13 Information in this section is from Joshua Kucera, “SOCOM Selects New Assault Rifle,” Jane’s Defence Weekly,
(continued...)
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accommodate three different barrels—a standard 35.7 cm barrel, a 25.5 cm close-combat barrel,
and a sniper variant barrel. All barrels reportedly will take less than five minutes to switch. The
SCAR-L is intended to replace USSOCOM M4-A1 carbines and features the same type of gas
piston operating system that the HK 416 employs.
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The Army describes the Asymmetric Warfare Group (AWG), based in Ft. Meade, MD, as an
Army special missions unit consisting of carefully selected military, Department of the Army
Civilians, and contractors who “observe and collect information about the evolving asymmetric
operating environment by providing advisors to deployed and deploying forces in support in the
Global War on Terrorism.”14 The Army reportedly initially approved AWG acquisition and use of
HK-416s in lieu of M-4s, but then reversed this decision stating, “The AWG also advises units on
training, tactics, and procedures. In this capacity, the use of the standard issue M-4 is required. In
support of this mission set, the decision was made to transition to the M-4 and the AWG is now
turning in its H&K rifles.”15 A report maintains that AWG “fought to keep its several hundred
416s, arguing that they outperform the Army’s M-4 and require far less maintenance.” Because
the HK-416 operates in a similar fashion to the M-4 and has comparable performance
characteristics, it is unlikely that training, tactics, and procedures vary greatly between the two
weapons, thereby causing some to question the motives behind the Army’s decision to recall the
AWG’s HK-416s.
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A 2002 Marine Corps Systems Command test was said to have concluded that the M-4
malfunctioned three times more often that the M-16A4, as the M-4 failed 186 times for a variety
of reasons over the course of 69,000 rounds fired, while the M-16A4 failed 61 times.16 In a test
conducted by the Army between October 2005 and April 2006, 10 new M-16s and 10 new M-4s
were fired in a 35,000-round test under laboratory conditions, with both weapons firing
approximately 5,000 rounds between stoppages.
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In April 2007, Senator Tom Coburn (R-Oklahoma) sent a letter to then Acting Secretary of the
Army Peter Geren questioning why the Army planned to spend $375 million on M-4 carbines
through FY2009 “without considering newer and possibly better weapons available on the
(...continued)
February 5, 2005, p. 8.
14 See 2008 U.S. Army Posture Statement Information Paper—Asymmetric Warfare Group http://www.army.mil/aps/
08/information_papers/prepare/Army_Asymmetric_Warfare_Group.html, accessed May 20, 2008.
15 Information in this section is from Matthew Cox, “Army Takes HK416s From Special Unit,” Army Times, March 11,
2008.
16 Matthew Cox, “Better Than M4, But You Can’t Have One,” Army Times, March 1, 2007.
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commercial market.”17 Senator Coburn’s letter also cited M-4 reliability and lethality concerns
and called for a competition to evaluate alternatives to the M-4, citing a need to conduct a “free
and open competition.” The Army initially agreed to begin the tests in August 2007 at the Army
Test and Evaluation Center at Aberdeen Proving Ground, MD, but then postponed the test until
December 2007.18 The test evaluated the M-4 against the HK-416, the HK -XM8, and the FNH
SCAR, with each weapon firing 6,000 rounds under sandstorm conditions. Officials reportedly
evaluated 10 each of the four weapons, firing a total of 60,000 rounds per model resulting in the
following: XM-8, 127 stoppages; FNH SCAR, 226 stoppages; HK-416, 233 stoppages; and the
M-4, 882 stoppages.19 On December 17, 2007, when the Army briefed Congress and the press,
the Army reportedly claimed that the M-4 suffered only 296 stoppages during the test, explaining
that the stoppage discrepancy from the original 882 M-4 stoppages reported could have been due
to the application of the Army Test and Evaluation Center’s post-test Reliability, Availability, and
Maintainability (RAM) Scoring Conference.20 This process attributes failures to such factors as
operator error or part failure and, as an example, if evaluators linked 10 stoppages to a broken
part on a weapon, they could eliminate nine of the stoppages and count only one failure for
reporting purposes. It is not known whether the Army also applied the RAM process to the other
three weapons in the test, but it might be assumed that if the other three weapons were given
equal treatment, those weapon’s stoppages would also likely be decreased in a manner similar to
the M-4.
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The House and Senate approved the Administration’s FY2009 M-4 Budget Request (see H.R.
5658 and S. 3001, FY2009 National Defense Authorization Act). Accompanying H.Rept. 110-
652, May 16, 2008, calls for the services to work together to develop and resource a joint, long-
term competitive strategy for small arms, including a “next-generation carbine.” S.Rept. 11-335,
May 12, 2008, recommends “that Secretary of Defense submit a report on the feasibility and
advisability of conducting a full and open competition for carbine-type weapons.” (Sec.112,
S.Rept. 11-335).
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In August 2008, the Army issued a request for information to the small arms industry seeking
information on “the state of the art in small arms technologies.” This request is viewed by some
as the first step in a carbine competition that the Army intends to conduct sometime in 2009 after
Colt Defense turns over the M-4’s technical data rights in June 2009. The Army plans to release a
request for proposal (RFP) in the late summer of this year requesting prototype weapons for
testing. Army officials have stated that they will consider other caliber weapons other than the
17 Information in this section is from Matthew Cox, “Competition Sought for New Army Rifle,” Army Times, April 27,
2007.
18 Matthew Cox, “Army Tests of Rival Carbines Postponed,” Army Times, September 20, 2007.
19 Matthew Cox, “New Carbines Outperform M-4 in Dust Test,” Army Times, December 17, 2007.
20 Information in this section is from Matthew Cox, “Giving M-4 Failures an Alibi,” Army Times, December 29, 2007.
21 Matthew Cox, “U.S. Army Asks Industry for an M-4 Replacement,” Army Times, October 6, 2008 and Matthew
Cox, “Army Solicits Industry for M-4 Replacement,” Army Times, September 29, 2008.
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current 5.56mm. Factors that the Army will consider in its evaluation are improved accuracy,
durability in all environments, and modularity.
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It can be argued that the M-4 is generally well-regarded by the soldiers who use it in combat and
its lethality may be more a function of the round used as opposed to the actual weapon itself. One
potential option for gaining greater insight into this issue might be to outfit selected Army
infantry companies (about 120 soldiers) in both Iraq and Afghanistan with XM-8s, HK-416s, and
FNH SCARs for a comparative study with an infantry company equipped with M-4s. Such a
study, conducted in combat as opposed to in laboratories and on firing ranges, might provide what
could be described as “the ultimate test” of these weapons. Such testing is not unprecedented, as
the Army has tested its Land Warrior integrated modular combat system in Iraq with an infantry
battalion in actual combat. Such a field test might also be worth considering when the Army
begins evaluating prototype M-4 replacement weapons.
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It has been suggested that USSOCOM’s decision to adopt the FNH SCAR has implications for
the Army. In one sense, the SCAR is the first modular small arms system adopted by the military.
The SCAR-L and SCAR-H will replace the following weapons: M-4A1, MK-18 close quarter
carbine, MK-11 sniper security rifle, MK-12 special purpose rifle, and the M-14 rifle.22 There is
also a 90% parts commonality between the SCAR-L and SCAR-H, including a common upper
receiver and stock and trigger housing and an enhanced grenade launcher can be attached to
either model.23 While the SCAR might not meet all of the conventional Army’s requirements, its
adaptability in terms of missions (close quarters combat to long-range sniper operations), being
able to rapidly convert from a 5.56 mm to a 7.62 mm weapon, and the ability to accommodate a
variety of modifications such as grenade launchers and special optics, might be factors worth
considering as the “modular Army”plans future small arms programs.
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Andrew Feickert
Specialist in Military Ground Forces
afeickert@crs.loc.gov, 7-7673
22 Scott R. Gourley, “Soldier Armed: Special Operations Forces Combat Assault Rifles,” Association of the U.S. Army
(AUSA) Army Magazine, May 1, 2006.
23 Nathan Hodge, “Stopping Power,” Jane’s Defence Weekly, July 25, 2007.
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