The Army’s M-4 Carbine: Background and
Issues for Congress
Andrew Feickert
Specialist in Military Ground Forces
August 3, 2009
Congressional Research Service
7-5700
www.crs.gov
RS22888
CRS Report for Congress
P
repared for Members and Committees of Congress
The Army’s M-4 Carbine: Background and Issues for Congress
Summary
The M-4 carbine is the Army’s primary individual combat weapon for infantry units. While there
have been concerns raised by some about the M-4’s reliability and lethality, some studies suggest
that the M-4 is performing well and is viewed favorably by users. The U.S. Special Operations
Command (USSOCOM) is replacing its M-4s with the Special Operations Combat Assault Rifle
(SCAR), and some USSOCOM units are expected to deploy into combat with the SCAR. The
Army is currently examining the possibility of initiating an open competition to replace the M-4.
This report will be updated as events warrant.
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The Army’s M-4 Carbine: Background and Issues for Congress
Contents
Background ................................................................................................................................ 1
Concerns with M-4 Reliability and Lethality ............................................................................... 1
USSOCOM M-4A1 Study..................................................................................................... 1
Soldier Weapons Assessment—Operation Iraqi Freedom....................................................... 2
Center for Naval Analyses (CNA) Study on Small Arms in Combat ...................................... 2
Special Forces Opts to Replace the M-4 ...................................................................................... 3
U.S. Army Rangers to Employ SCAR in Combat .................................................................. 4
Congressionally Requested M-4 Test..................................................................................... 4
U.S. Army Small Arms Capabilities-Based Assessment (CBA).............................................. 5
An Examination of the Small Arms Capability-Based Assessment ................................... 6
Army Looks for a Replacement for the M-4 .......................................................................... 6
Department of Defense Conducts a Service-Wide Review of Small Arms .............................. 7
Potential Issues for Congress....................................................................................................... 7
M-4 Performance and Reliability........................................................................................... 7
DOD’s Small Arms Review Versus the Army’s Plan to Replace the M-4................................ 7
USSOCOM Implications of Replacing M-4s ......................................................................... 7
Contacts
Author Contact Information ........................................................................................................ 8
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The Army’s M-4 Carbine: Background and Issues for Congress
Background
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 and have suggested 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
Concerns with M-4 Reliability and Lethality
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 Other reports, however, suggest that the M-4 has
performed well and generally well-received by troops.
USSOCOM M-4A1 Study5
In February 2001, USSOCOM published a study and analysis of alternatives focused on the M-
4A1 carbine used by USSOCOM units. The study concludes that the M-4A1 design was
fundamentally flawed—in part due to barrel and gas tube shortening—and that a variety of
factors “led to alarming failures of the M-4A1 in operations under the harsh conditions and heavy
firing schedules common in SOF training and operations.”6 While USSOCOM concluded in 2001
that the M-4A1 carbine in its current configuration did not meet SOF requirements,7 USSOCOM
noted that the shortfalls that they identified had not become evident in conventional Army units
that used the M-4, likely due to the “newness” of the weapon and the lower firing schedules of
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 from this section is taken from USSOCOM Study: “M-4A1 Carbine and Related Systems Deficiencies
and Solutions: Operational and Technical Study With Analysis of Alternatives,” February 23, 2001.
6 Ibid., p. 5.
7 Ibid., p. 20.
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The Army’s M-4 Carbine: Background and Issues for Congress
conventional unit training.8 USSOCOM further noted that the M-4 met or exceeded the Army’s
specifications for reliability and that the M-4 met the needs of the conventional Army.9
Soldier Weapons Assessment—Operation Iraqi Freedom10
In July 2003, the Army published a report to assess small arms performance during Iraqi
Freedom. Army personnel interviewed over 1,000 soldiers to assess what “worked well and what
did not.” The assessment was generally favorable toward all small arms examined and did not
employ any discernable analytic metrics. The assessment stated that the M-4 was “by far the
preferred individual weapon across the theater of operations”11 and recommended in the “near
term replace the M-16 with the M-4 as the standard issue weapon”12 but without any
corresponding analytical data, some might question the validity of the Army’s assessment.
Center for Naval Analyses (CNA) Study on Small Arms in
Combat13
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
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).
8 Ibid., p. 6.
9 Ibid., p. 6.
10 Information in this section is taken from Project Manager Soldier Weapons, “Soldier Weapons Assessment Team
Report 6-03: Operation Iraqi Freedom,” July 31, 2003.
11 Ibid., p. 34.
12 Ibid., p. 35.
13 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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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.
Special Forces Opts to Replace the M-414
In USSOCOM’s February 2001 study, a number of M-4 reliability problems were documented.15
The USSOCOM report 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 reported 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.16
In addition to reliability problems detailed in USSOCOM’s February 2001 study, another possible
reason that USSOCOM might have wanted to replace the M-4 carbine is that because the M-4
was a weapon procured by the Department of Defense and subject to military standards and the
technical data package, meaning that USSOCOM could not make changes to the weapon. If
USSOCOM became the procurement agency for a new carbine, then they could direct the
carbine’s manufacturer to make changes and modifications.
In early 2003, USSOCOM officials initiated efforts to identify potential new combat rifle
capabilities.17 From May through August 2004, USSOCOM evaluated 12 weapons from nine
different manufacturers.18 In November 2004, USSOCOM awarded a contract to FNH USA19 to
develop the Special Operations Combat Assault Rifle (SCAR).20 The SCAR will come in two
variants—the heavy 7.62 mm SCAR-H and the light 5.56 mm SCAR-L. 21 Each variant will
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.
14 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.
15 USSOCOM Study: “M-4A1 Carbine and Related Systems Deficiencies and Solutions: Operational and Technical
Study With Analysis of Alternatives,” February 23, 2001.
16 Matthew Cox and Kris Osborn, “M4,In Their Sights,” Defense News, February 25, 2008.
17 Scott R. Gourley, “Soldier Armed: Special Operations Forces Combat Assault Rifles,” Association of the U.S. Army
(AUSA) Army Magazine, May 1, 2006.
18 “US SOCOM Awards Contract for SCAR Development,” Jane’s International Defense Review, January 2008, p. 26.
19 FNH USA is the U.S.-based sales and marketing entity for the Belgium-based FN Herstal S.A.
20 Scott R. Gourley, “SCAR Evaluation Nears Conclusion,” Jane’s Defence Weekly, March 19, 2009, p. 12.
21 Information in this section is from Joshua Kucera, “SOCOM Selects New Assault Rifle,” Jane’s Defence Weekly,
February 5, 2005, p. 8.
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U.S. Army Rangers to Employ SCAR in Combat22
In April 2009, the first 600 of 1,800 SCARs to be issued to USSOCOM were fielded to units of
the 75th Ranger Regiment, and reports suggest that the Rangers will deploy into combat with the
SCAR. Because this is the first known large-scale deployment of this weapon into combat, there
will likely be a significant amount of evaluation of the SCAR’s reliability and performance.
These evaluations may prove useful to the Army as it examines the future of small arms.
Congressionally Requested M-4 Test
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
commercial market.”23 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 2007.24 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.25 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.26 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.
The M-4’s developer, Colt Defense, LLC, contends that there were a number of factors during the
test that might have resulted in testing discrepancies.27 Among the issues raised, the Colt M-4
carbines used for the test were drawn from the Army’s inventory and did not meet military
specifications but were used in the test, whereas weapons tested from other manufacturers were
provided from the manufacturers. Another point of contention was that the M-4 carbines were
three-round burst weapons and the other weapons tested were fully automatic. It was also alleged
that testers did not know how to operate the three-round burst M-4s in both the laboratory
environment and in a related test at Aberdeen Proving Grounds and, therefore, mistakenly
reported M-4 stoppages, resulting in inflated results. Given these and other allegations, it is
22 Information in this section is taken from Matthew Cox, “75th Rangers Will Take Scar Into Combat,” Defense News,
May 11, 2009.
23 Information in this section is from Matthew Cox, “Competition Sought for New Army Rifle,” Army Times, April 27,
2007.
24 Matthew Cox, “Army Tests of Rival Carbines Postponed,” Army Times, September 20, 2007.
25 Matthew Cox, “New Carbines Outperform M-4 in Dust Test,” Army Times, December 17, 2007.
26 Information in this section is from Matthew Cox, “Giving M-4 Failures an Alibi,” Army Times, December 29, 2007.
27 Information in this section is from a briefing given to CRS by Colt Defense, LLC on July 14, 2009.
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possible that testing conditions during the December 2007 test were not consistent, calling into
question the validity of the results.
U.S. Army Small Arms Capabilities-Based Assessment (CBA)28
On January 21, 2009, the Secretary of the Army provided the House and Senate Armed Services
Committees with the findings of the U.S. Army Infantry Center Small Arms Capabilities-Based
Assessment (CBA), which had been completed in April 2008. The Army, as the Department of
Defense (DOD) Executive Agent for Small Arms (SA), conducted the Small Arms CBA to
establish and support a small arms acquisition strategy through 2015. This analysis examined 10
tasks, as described below:
1. Engage threat personnel with SA fire.
2. Engage threat personnel that are in defilade.29
3. Engage threats with precision SA fire.
4. Engage threats with SA volume fire.
5. Acquire personnel and vehicle targets.
6. Determine range to target.
7. Mark or tag targets.
8. Breach existing entry points.
9. Avoid detection caused by weapon signature.
10. Operate and maintain weapons.
Based on analysis, the study team identified 25 capability gaps associated with the 10
aforementioned tasks, as well the overall requirement from individual soldiers and their leaders
that they required “greater lethality” and “more knockdown power.” The study team identified a
number of non-material and material recommendations to address the identified capability gaps.
Non-material solutions—which are preferable because they can be implemented relatively
quickly and inexpensively—included improving training, updating doctrine, using additional SA
ancillary devices (example: optics), developing a Small Arms Weapons Expert Program at
battalion and brigade level, and adding a Weapons Repairman at company level. Material
solutions included developing special airburst munitions to engage defilade targets; developing
ammunition that would be more lethal at short ranges (0 to 200 meters); improving breaching and
non-lethal marking 40 mm rounds; improving combat optics; developing a new weapon system
for vehicle and aircraft crews that provides greater maneuverability in confined spaces and
provides more firepower than a pistol; and developing SA weapons that require fewer and simpler
tools to maintain and that would require less cleaning and lubrication. Another recommendation
was that any new SA developed to meet these capability gaps needed to contribute to lightening
the soldier’s overall combat load.
28 Information in this sections is from the U.S. Army Infantry Center Small Arms Capabilities Based Assessment
provided to Congress on January 21, 2009.
29 Defilade is defined as protection provided from hostile fire provided by an obstacle such as a hill, ridge, or bank; a
vertical distance by which a position is concealed from enemy observation; or to shield from enemy fire or observation
by using natural or artificial obstacles.
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The study identified 42 separate Ideas for Material Solutions (IMAs) to address capability gaps
that required a material solution. Of these 42 IMAs, 13 involved creating new munitions or
improving existing munitions, and 10 involved aiming devices, optics, or laser designators; only 7
IMAs suggested modifying current SAs or developing new SAs. Other IMAs included
suggestions such as improving munitions propellants and improving weapon magazines.
Secretary Geren’s January 21, 2009, letter to House and Senate Armed Service Committee
Leadership stated that “following the completion of the CBA, the Army decided to update the
requirement for combat rifle/ carbine and compete this updated requirement in an open
competition.”
An Examination of the Small Arms Capability-Based Assessment
The Army’s SA CBA appears to be a comprehensive assessment of DOD’s small arms
requirements that incorporates a great amount of analytical data and many observations derived
from combat operations in Iraq and Afghanistan. It can be argued that the CBA does not present a
compelling case to develop and acquire a new combat rifle or carbine. Many of the CBA’s
recommended material solutions involve improved or new munitions or ancillary items such as
optics or weapons magazines. The CBA does call for the development of a new SA system for
vehicle and aircraft crew and an extended-range heavy machine gun, but nowhere explicitly calls
for a new combat rifle or carbine. It is possible that many of the CBA’s proposed material
solutions might be readily adaptable to current combat rifles (M-16s) and carbines (M-4s) with
little or no modification to the weapon. In this regard, a totally new design might be required only
if new munitions, optics, other ancillary items, and reliability improvements are totally
incompatible with SAs currently in use. The majority of the deficiencies cited in the SA CBA do
not directly fault the current combat rifle or carbine, but instead call for ammunition, sight, and
optic improvements, which might not in and of themselves appear to justify undertaking a
potentially lengthy and costly development and procurement effort.
Army Looks for a Replacement for the M-430
Based in part on the results of the Small Arms CBA, the Army issued a request for information in
August 2008 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
2009 requesting prototype weapons for testing. Army officials have stated that they will consider
other caliber weapons other than the current 5.56mm. Factors that the Army will consider in its
evaluation are improved accuracy, durability in all environments, and modularity.
30 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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Department of Defense Conducts a Service-Wide Review of Small
Arms31
DOD is currently conducting a service-wide review of small arms requirements that some believe
could “challenge the Army’s decision to search for a new carbine.”32 This review involves small
arms experts from each service as well as experts from the small arms industry and is intended to
“map out a common strategy for the Defense Department’s individual and crew-served weapons
needs.”33 The DOD review team is currently said to be reviewing the Army’s Small Arms CBA
and was supposed to have developed a set of conclusions by the end of May 2009.
Potential Issues for Congress
M-4 Performance and Reliability
Based on the aforementioned studies and tests, there appears to be not only a wide range of
opinions as to the M-4’s reliability and lethality, but also questions if testing of the M-4 has been
consistent and whether performance results are indeed accurate. If the Army does opt to replace
the M-4 and the competition involves comparative testing, efforts might be undertaken to ensure
consistency between test weapons.
DOD’s Small Arms Review Versus the Army’s Plan to Replace the
M-4
As previously noted, the Army is basing its upcoming carbine competition to a large extent on the
Small Arms CBA, which some believe does not present a compelling case to launch a
competition to replace the M-4. According to reports, DOD—as part of its joint small arms
review—is supposed to shortly reach a number of conclusions about the Army’s Small Arms
CBA that might be relevant to any planned M-4 replacement competition. The results of DOD’s
review might possibly support the Army’s planned M-4 replacement competition or instead
suggest an alternative course of action. Congress might benefit from examining the results of
DOD’s service-wide small arms review as it considers the future of the Army’s small arms
modernization efforts.
USSOCOM Implications of Replacing M-4s
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.34 There is
31 Information in this section is from Matthew Cox, “Program Reviews Could Affect Carbine Search,” Army Times,
April 25, 2009.
32 Ibid.
33 Ibid.
34 Scott R. Gourley, “Soldier Armed: Special Operations Forces Combat Assault Rifles,” Association of the U.S. Army
(continued...)
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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.35 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. The Ranger’s forthcoming
combat deployment with the SCAR and associated lessons learned and performance and lethality
data might also have implications for future Army small arms development and acquisition
efforts.
Author Contact Information
Andrew Feickert
Specialist in Military Ground Forces
afeickert@crs.loc.gov, 7-7673
(...continued)
(AUSA) Army Magazine, May 1, 2006.
35 Nathan Hodge, “Stopping Power,” Jane’s Defence Weekly, July 25, 2007.
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