Today, a variant of the Heckler & Koch HK416 rifle is the standard squad infantry automatic rifle (IAR) of the United States Marine Corps, as the M27. At one time in the mid-2000s, though, companies from Colt to LWRC competed against each other in a competition to see which weapon would be the the Corps’ choice to fill the role, supplanting the belt-fed M249 as the squad’s automatic fire support capability. These weapons took a variety of approaches to meeting the USMC’s needs, from the constant recoil Ultimax MG, to the heat-sink equipped Colt IAR, to the open bolt full auto, closed bolt semiauto LWRC IAR. Ultimately, simplicity won out, and Heckler & Koch’s quite unambitious HK416-derived entry was selected to be the M27.

Recently, a source sent TFB a FOIA request that they had filed with the USMC’s Systems Command (SYSCOM) regarding the test results of the original IAR trials, and the results are a bit surprising. The original USMC standards for these trials were that the weapons should achieve at least 900 mean rounds between Class I and II failures (MRBF), and an objective 5,000 MRBF. The test put 2,400 rounds through each Unit Under Test (UUT) at both ambient and hot and cold conditions. The exact procedure is replicated below:

Excerpts from the Test Evaluation Report for the Infantry
Automatic (IAR) Bid Samples 2008

1. Environmental Testing

a. Environmental testing was not conducted in the Test
Evaluation Plan.

2. Reliability Testing

a. The Unit Under Test (UUT) shall have a Mean Rounds Between
Failure (MRBF) of 900 for Class I and II failures combined
(Threshold), 5,000 MRBF (Objective).

(1) Class I failure: A failure that may be immediately
corrected by the operator within 10 seconds or less while
following prescribed immediate action procedures.

(2) Class II failure: A failure that may be corrected by
the operator, and that requires more than 10 seconds but not
more than 10 minutes to correct (less the TM/OM defined cool
down period if a hot barrel condition exists). Only the
equipment and tools issued with the weapon may be used to
correct the failure.

b. Each UUT shall safely function through 300 rounds each at
a temperature range of -25°F and 160°F, and 1800 rounds per UUT
fired at 77°F ±18°F.

c. Evaluation Procedure

(1) Conditioned the UUTs (loaded weapons condition 3) for
a minimum of 4 hours to 77°F ±18°F.

(2) Fired 60 rounds in automatic mode – 3 to 5 round
bursts at a rate of 30 rounds per minute.

(3) Fired 60 rounds in semi-automatic mode – at a rate of
30 rounds per minute. (4) Allowed UUT to cool so that the barrel temperature did
not exceed 120°F.

(5) Repeated steps 2 through 4 until there had been five
total firing iterations (600 rounds fired).

(6) Allowed UUT to cool. Cleaned and lubricated each UUT.

(7) Repeated steps 2 through 6 until 1800 rounds had been
fired by each UUT at this temperature.

(8) Conditioned the UUTs (loaded weapons condition 3) for
a minimum of 4 hours to 160°F.

(9) Fired 30 rounds in automatic mode – 3 to 5 round
bursts at a rate of 30 rounds per minute.

(10) Fired 30 rounds in semi-automatic mode – at a rate of
30 rounds per minute.

(11) Allowed UUT to cool so that the barrel temperature did
not exceed 200°F.

(12) Repeated steps 9 through 11 until 300 rounds had been
fired by each UUT at this temperature.

(13) Allowed UUTs to cool. Cleaned and lubricated each
UUT.

(14) Conditioned the UUTs (loaded weapons condition 3) for
a minimum of 4 hours to -25°F.

(15) Fired 30 rounds in automatic mode – fired in 3 to 5
rounds bursts at the rate of 30 rounds per minute.

(16) Fired 30 rounds in semi-automatic mode – fired at the
rate of 30 rounds per minute.

(17) Allowed UUT to cool so that the barrel temperature did
not exceed 15°F. (18) Repeated steps 15 through 17 until 300 rounds had been
fired by each UUT at this temperature.

(19) Allowed UUTs to cool. Cleaned and lubricated each
UUT.

d. Procedures 1 through 7 were conducted by MCSC personnel.
Procedures 8 through 17 were conducted by Aberdeen Proving
Ground due to temperature requirements that are outside the
current capabilities of the MCSC.

e. All participants submitted three samples for testing.

Which means that each entrant was subjected to 7,200 rounds over three units. The results were:

f. Results for all Class I and II failures are listed below
across all 3 UUTs from 9 of the 10 IAR Bid Samples.

(1) Colt proposal A: 60 Failures

(2) Colt proposal B: 28 Failures

(3) Competitor C: 23 Failures

(4) Competitor D: 78 Failures

(5) Competitor E: 39 Failures

(6) Competitor F: 12 Failures

(7) Heckler & Koch Defence Inc. proposal G: 27 Failures

(8) Competitor H: 124 Failures

(9) FN Herstal proposal J: 26 Failures

g. The 10th IAR Bid Sample, Competitor I, was determined
unsafe for live fire due to a lack of proof marking. Live fire
testing was not conducted.

Only the competitors who made it to the final downselect are identified in the results, those being Colt’s IAR A and IAR B, H&K’s HK416 IAR, and FN’s HAMR. Of special note is that the Colt 6940 IAR, a direct impingement weapon, proved to be only slightly less reliable than H&K’s operating rod-equipped HK416 IAR. These days this probably isn’t a surprise to many people, but at the time of the trials all the right-thinking people were sure that rifles using operating rods in lieu of direct impingement would work far better. What a coup these results would have been!

To me, the most likely reason for the HK416’s selection as the IAR was its resemblance to existing weapons. One of the requirements of the program was that the new IAR should not “stick out” in a group of Marines armed with M16A4 Rifles and M4 Carbines. Of the weapons tested that gave good results in reliability, the HK416 was the one that looked the most like the existing weapons.

Of course, there is also the theory that the HK416 was selected because the IAR competition was a backdoor to replace the USMC’s existing rifles and carbines, and while that doesn’t seem to have really been the case, there isn’t zero truth to that idea.