Moderator: Hitoru
by Liam on Wed Apr 16, 2008 11:52 am
the problem with the M4 is the frigging shortened gas tube.
the gas vent that is drilled in the barrel incrementally increases in size after as little as a thousand rounds fired. With the increase in size, the gases flowing back into the bolt carrier gas key are greater, this causes the bolt carrier to cycle faster, and at a certain point, it begins to cycle faster than the moment of obturation which causes the empty shell casing from the fired round to stick in the chamber, which overcoming the extractor claws holding power, the bolt carrier goes to the rear, and moves forward, stripping the next round from the magazine, which impacts the stuck casing, and causes a nasty jam that requires clearing the weapon and using a hard punch rod to extract the empty shell casing.
The moment of obturation is a fascinating trait of brass shell casings. Upon firing the brass expands under pressure to fill the chamber and form a reliable gas seal, then a fraction of a second later,as pressure bleeds of slightly, it contracts back a little and releases from the chamber walls, allowing itself to be pulled from the chamber. The M4 has a nasty habit of trying to pull out the shell casing before this contraction has occurred all the way.
The shorter barrel places the gas vent hole closer to the chamber, and superheated gases erode it a phenomenal rate compared to a regular 20 inch barrel M16. More gas=more fouling in the receiver, to the laymen this is the cause of his jams, so he tries to clean it more often, but since the problem is timing of the gas system, the operator cannot fix it. This flaw is inherent to the weapon, not the environment or the operator maintainence.
It has nothing to do with being sensitive to the environment any more than a regular M16. The damned thing is a malfunction prone modification to a fine tuned system, it was never meant to be shortened the way it was apparently. In some circles they call this the law of unintended consequences. The short barrel also lowers the range at which the 5.56mm bullet fragments, which is the key to its wounding potential. Somewhere around 125 meters it stops fragmenting, in a 10 inch barrel that distance is around 75 meters. The 5.56mm just has to have high velocity to give it terminal performance. So you end up with a less effective weapon that now is unreliable after a short service period, it was fine while new, but after a few years of regular usage, it shows itself to be a lemon, the more you fire it, the more likely it will start to malfunction.
Gas piston operated weapons are in general more robust. The Direct Gas Impingement system of the M16 is a unique snowflake among weapons. Switching to a gas piston operated M16 fixes the problem, but not for the reasons given, just as a side effect.
If the Army spent more time teaching and understanding weapons, they would see this as obvious and not need to have to have SF types figure it out in field usage, and they are still pointing fingers at the wrong cause. All it takes is a few telephone calls to weapons design experts and engineers.
there now you have the dirty little secret to the whole shebang.
The M16/M4 reliability issue begins with the weapon’s gas system, which in the words of another journalist, “vomits into its own mouth.” The Ljungman-type direct impingement gas system is simple and lightweight, but it blows hot gases, carbon fouling and unburned powder particles directly back into the weapon’s receiver. Not only does this require intensive maintenance, but heavy lubrication to keep the fouling soft and the rifle operating. In the hostile Iraq environment where dust the consistency of talcum powder gets into everything, the lubricant becomes a “dust magnet,” causing frequent stoppages (jams) – just what you need in a firefight! Both M16 and M4 weapons have this problem. Anyone who has ever cleaned an M16 or M4 remembers the caked on carbon fouling that must literally be scraped off the internal components of the bolt carrier assembly.
In the case of the M4, the gas problem is made even worse because the gas port has been moved back to within six inches or so of the upper receiver, meaning that gases entering the receiver are hotter and under higher pressure than those of the longer barreled M16. The hotter, higher pressure gases not only raise the operating temperature in the forward area of the upper receiver, but also in the magazine well area. Just as bad, the gases cause accelerated gas port erosion, further raising pressures and dumping even more hot gases into the upper receiver. Higher pressures cause timing issues, which results in the weapon unlocking before pressures in the barrel have dropped and while cartridge cases are still clinging to the chamber wall, blowing extractors, breaking bolts and stripping locking lugs. A partial solution to this issue is to replace the direct impingement gas system with a gas piston and operating rod system.
Liam wrote:Yes indeed the gas port in the barrel erodes, it is a known fact. Just because your rifle hasn't done it, and you really can't quantifiably say it has or hasn't... neither can your armorer usually.
This very issue of gas system timing has been kept hush hush...
research it a bit, your layman's view is quaint, but wrong.
Yes.How much have you fired your rifle? 1000s of rounds?
It is a 100% legal non-nfa civilian owned model, so no.Is it capable of burst fire?
How many mags of ammo have you dumped in rapid fire one after another?
I currently have a BRAND NEW M4 issued to me, I am the only person to shoot it, and it works fine.
Let me ask you a question...How do you think it is possible for combustion gas to erode a hole that is cut in hardened steel? Does that seem right to you?
Liam wrote:yes hot propellant gases do damage barrels... it happens all the time, what the fuck do you think wrecks magnum rifle barrels like .300 Winchester Magnum?
"It is true that erosion is caused by the blow torch effect of powder gasses
and solids striking the rifling. One forgets that a large amount of
powder travels down the barrel at the speed of gas. If you really want
to see the damage this can cause look at the cone of a muzzle brake on a
50 cal and see where powder kernels have peaned the hole over until it
causes the bullet to strike the brake."
-From Gale McMillian.
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