The M4 carbine traces it origins back to the M16A2 and some of its variants, Colt Defense developed it and has been in production since 1994, and in service since 1997. The M4 is a gas operated, magazine feed selective fire weapon. Its other features include a 14.5 inch barrel, collapsible buttstock a trigger pack that delivered a 3 shot burst, a feature that was discontinued with the introduction of the M4A1; giving the operator full automatic capabilities.
The original driver behind the design was a pressing need to provide mobile personnel with a weapon that could be more easily carried in a tank, truck or where space is a consideration. Over the years the M4 / M4A1 has undergone a number of changes including modifications requested by USSOCOM under SOPMOD Block I and Block II. Currently, the Army is looking at a variety of other modifications including a change to the operating system from direct gas impingement to a piston driven.
Driven by a number of highly publicized complaints, and Congressional arm-twisting, late in 2008, the Army embarked on a future carbine replacement program. It is now three years later, 2011, and a replacement carbine has yet to be identified. Regretfully and unfairly, the Army has been taking the blunt of the criticism. With criticisms ranging from the Army is placing lives at risk to they are biased and in bed with Colt Defense.
The reality is that the decision needs to be made with a holistic view and with the clear understanding that the project entails much more than issuing a contract. The decision the Army makes will have significant consequences fiscally and logistically. Is the M4 or M4A1 a flawed design, or are we failing to recognize that like all mechanical systems exposed to high pressures, heat and friction need maintenance? Rather than jump directly into the issues, I’d like to risk boring some readers to give others a simplified background on the M4’s operating system, I think it would provide some clarity.
The M4 and M4A1 use a gas operating system, and unlike a piston driven carbine, the gas system on an M4 has no moving parts. During the manufacturing process, a pinhole is drilled into the barrel at a point just behind the muzzle. That pinhole has the precise dimension needed to sample the gas in the bore; returning it back to the receiver via a gas tube. The gas pressure sent back to the receiver acts on the bolt carrier, unlocking the bolt, extracting the spent case, ejecting the spent case, setting the trigger, impacting the buffer and compressing the recoil spring. At this point, the compressed recoil spring returns the bolt and carrier forward, which strips a new round from the magazine, chambers it and locks the bolt for the next shot. In fully automatic fire, the cycle takes place at 11.7 time per second. So, what is it that can go wrong with this system?
- Although highly unlikely, the gas system could fail – the pinhole (gas port) or gas tube could become clogged. This is particularly true in waterborne operations. However, because of the gas pressure presented to the gas system clogging or fouling is a non-issue; we generally agree that it is self-cleaning. In the 20+ years of experience that I’ve had with M16 and M4 platforms, I have never experience a gas system failure. The distinct advantage that a piston driven system has over the direct gas impingement is that hot gasses are never allowed to enter the receiver thus reducing heat related failures and fouling, particularly when the carbine is suppressed. The trade-off is that your gas processing mechanism now has moving parts potentially increasing the probability of failure.
- Next on the list of failure points is the bolt. In addition to housing the firing pin and locking the round in the chamber, the bolt also handles extraction and ejection. If not properly cleaned and lubricated, this subassembly can lead to weapon stoppages. A broken extractor will prevent the operator from extracting a spent shell casing making the weapon inoperable, and if it happens in the middle of a firefight it could be lethal. This is particularly true in CQB/CQC engagements. The only field expedient solution to this problem is replacing the bolt assembly. Fortunately this is a procedure that takes two minutes or less.
- Magazines are also famous for causing weapon stoppages. Dirty magazines are at the top of the list for root causes of magazine failures. Weak springs and damaged magazine housings (body or feed lips) also lead to failures. Overloading magazines can do it as well. I personally have put more than 30 rounds in a magazine and wondered why I couldn’t seat the magazine in the receiver.
- Finally, a weak or broken recoil spring will not return the bolt carrier forward with enough energy to strip and chamber a round or lock the bolt. If mud, dirt and grit enter the tube housing the recoil spring it can have adverse effects on the weapon’s operation.
- There are other issues like broken firing pins or damaged bolt assemblies but they are rare occurrences.
Having said all of the above, the truth of the matter is that all gas operated systems work basically in the same way. There is nothing that I know of, except a blowback operated weapon that gets around those mechanics.
Why is the Kalashnikov family so reliable? In its simplest terms, looser tolerances and fewer moving parts; however, that too has a cost and it’s manifested in a decrease in accuracy. However, that decrease is a change in minute of angle performance at 100 meters. The M4 /M16 is capable of 2MOA where an AK47 typically delivers 4 to 5 MOA. Is that necessarily a bad thing? A highly subjective measure.
The real question and one that PM Soldier Weapons is clearly focusing on is will a new carbine give the Army a greater than unity gain in performance over the current M4/M4A1? I honestly don’t think so, given the current state of the art. That does not mean that the FN SCAR or HK416 / 417, as all other entries, are not worthy considerations – they are, but is there a greater than unity gain, probably not.
However, something that I find troubling is the apparent absence of a bullpup design. Bullpup designs, like FN’s F2000 or the Israeli Tavor, keep overall length at a minimum yet retain the longer barrel that contributes to accuracy and lethality.
As of this writing, PM Soldier Weapons seems to be taking a systems approach, which is precisely the correct methodology in the selection process.
Look for more on this subject as the selection process moves forward.
FOG HORN 
