While waiting for my wife to shop I picked up a Special Weapons magazine. It was saying the M4 is unreliable. Torn Case Heads, Failure to Extract ect.

Being a Noob I want to know do these problems exist in say the Bushy M4 Types 14.5bbls?

While I realize they are not the same animal I'm just wondering if these problems plague the civilian semi-auto versions as well?

If someone could elaborate on this I would appreciate it!

Thanks

Quoted: While waiting for my wife to shop I picked up a Special Weapons magazine. It was saying the M4 is unreliable. Torn Case Heads, Failure to Extract ect. Being a Noob I want to know do these problems exist in say the Bushy M4 Types 14.5bbls? While I realize they are not the same animal I'm just wondering if these problems plague the civilian semi-auto versions as well? If someone could elaborate on this I would appreciate it! Thanks

My M4 is as reliable as my 20".  Both function perfectly.

6 outa the last 8 issues, they raved about the M4 and how awesome it is.

Hack job of a magazine...they are idiots.

They're horrible.  That's why the military stopped...oh wait...they are still issuing it.

Quoted: 6 outa the last 8 issues, they raved about the M4 and how awesome it is. Hack job of a magazine...they are idiots.

+1

It  depends on who wrote the article and what he was shillin g that day

M4 reliability issues are well documented and known by military weapons designers... Many steps have been taken to mitigate the problems and people are actively working on other answers right now.

Heavy buffers, stronger springs, extractor buffers, enhanced bolt carriers, reshaped extractors, issuing broken case extractors, pigtail and expansion chamber gas tubes, imroved magazine springs and followers... even a whole new rifle; these are some of the ideas that have been evaluated or are in use, all of which exist due to the questions of reliability with the M4.

Do some searching around on this site, there are many discussions about the most well known, notorious and exagerated problems with the M4...

is this the one when they've fallen inlove with the FN rifle?

Quoted: is this the one when they've fallen inlove with the FN rifle?

Yup..

well I guess that explains it huh?

ah well, I don't care, we were never issued M4s but the A2s held up quite well and I love my privately owned toys.

"Speshuwl Wepunz" magazine is only for l33t air5ofters and counter strike players.
They gush over one gun in one issue, then trash it the next.
I stopped reading it when I was 15.

I've been carrying a Colt M4 since Sept. of 2000. I've had several different ones, as weapons were assigned to squads. New squad, new rifle. Of those several rifles, I've had a couple magazine-related problems over the years since the mags you get from supply aren't always the best. Other than that, I've never had one fail to go bang when I needed it to. and that includes two Iraq deployments, Kosovo, three JRTC rotations, one NTC rotation, and a whole bunch of home-station training ranges, and have never seen a torn case head on anything but a .50 cal.

That pretty much wraps up the argument for me.

Thanks All!!!

I figured it beat the devil outta following the Ol Lady around so I read while she shopped!
Well it didn't cost me nuthing to read it! LOL

I appreciate your imput!

THANKS

Quoted: I've been carrying a Colt M4 since Sept. of 2000. I've had several different ones, as weapons were assigned to squads. New squad, new rifle. Of those several rifles, I've had a couple magazine-related problems over the years since the mags you get from supply aren't always the best. Other than that, I've never had one fail to go bang when I needed it to. and that includes two Iraq deployments, Kosovo, three JRTC rotations, one NTC rotation, and a whole bunch of home-station training ranges, and have never seen a torn case head on anything but a .50 cal. That pretty much wraps up the argument for me.

Well, it is a good thing you came along later in the game I guess? The M4 had been around for almost 15 years by the time you started packing one and many of the issues already addressed... but this still does not change the fact that the system did/does have some concerns.

Granted, many of them have been mitigated by heavy buffer and extra springs, but all of those things would have never been thought of if not for the original problems. I believe that many woudl still admit that the gas sytem is less than perfect as far as timing and pressures go, but yes... all things considered, it is a pretty damn good platform.

Depends on which Armchair Commando you talk to.  The 2005 SEBR is an M4 and I just blasted off 120 rounds today in a cold & rainy day in Michigan and that sweet bitch gave up her cookie and then some.

In other words shooting today was very enjoyable and 100% reliable.

If you want to get technical about it.  The carbine length gas system is hard on the extractor spring.  Overtime if/when the spring wears down you could/will get failure to extract issues...

Please investigate:
Wolff Extractor Spring
D-Fender
O-Rings
Black Colt Insert (Spring Buffer)

Class dismissed.

Private IM worth sharing...
----------------------------

Not sure who you work for, but I have been pulling triggers for Unlce Sam since 1979 and now I work as a firearms researcher for one of the larger military contractors... The "Armchair Commando" that I get a lot of info from is the guy that helped develope that M4 -- but I do deal and work with several people that have designs in service that go back as far the late 50s... but thanks for the "schooling"

-----------------------------

So there!!!  eat that!

-TheMocoMan-

Armchair Commando
DELTA

The vast majority are fine.  The few that have problems stem from the gas tube being shorter.  The gas blast that drives the bolt back is more violent with the short then with the long tubes.  Hence, the torn cases and failure to eject.

just remember if you buy quality (like colt) you won't have a problem.

here's what you do...

buy an M4setup... pour sand in it (i mean fill it up) with the bolt locked back.

THen put a mag in and see if it shoots...

If not send it to me and i'll pay for shipping

In order to understand this, there are a few things about the functioning of the AR that have to be defined, I am away from most of my notes and stuff, so most of the figures given are from memory... but should be pretty close. For this description, the standard rifle gas system is with the gas port located at 13.0" and having a 20" barrel... the standard carbine system is with the port at 7.5" and a barrel of 14.5"

The pressures at the gas ports are: 13.5K for the rifle and 26K for the carbine -- or twice as much.

The dwell time (the time that the gas system is charged with high pressure) is determined by the amount of barrel after the gas port. These are nearly identical between the rifle and the carbine.

Pressure from the port is regulated only by the size of the gas port and the diameter of the barrel.

These two factors determine the internal bolt pressure, the maximum pressure that is obtained in the bolt carrier/piston combination -- for the rifle this pressure is about 1000psi and for the carbine it is over 1500psi, half again as much.

When the rifle is fired, primer shot sets the bullet forward until it contacts the rifling, at this point the powder charge detonates and sets the shell case fully back, binds the action and start to propel the bullet. The bullet jumps slightly again and is etched by the rifling... it stops again very briefly as the pressures build to a point for the bullet to overcome the mechanical advantage of the rifling twist and the bullet starts to spin, at this point the chamber pressure is at max, 50K plus (there are some that believe there is another, third stop the bullet makes and some testing suggest this may be true).

As the chamber pressures start to climb, the brass case expands and becomes plastic, this is essential to seal the case in the chamber -- the correct term for this is Obturation, when the case is obturated and sealed, it is stuck in the chamber, practically welded in really.

The Lock Time, or the time that the action remains locked with no attempt to start unlocking is very important... on the rifle, the lock time is about 550 microseconds, the lock time for the carbine is about 375 microseconds -- this may not seem like much, but it is much shorter of a time, also keep mind that the chamber pressures are twice as high in the carbine when the unlocking starts.

What does all of this mean? When the carbine is fired, the system attempts to unlock earlier than intended and while the case is still fully obfucated... this results in the action bind delaying the unlocking and stressing the system. As the 5.56N is not drastically tapered, "squirting" is not a big problem in most guns. When the internal bolt pressures finally unlock the bolt, the velocity of the reward movement in the carbine is much higher than what the rifle was designed for, it also must start extraction of the obfucated case... as you know, the AR does not have any sort of initial extraction, perhaps the single biggest shortcoming of the design. This has been known to cause ripped case heads...

At this point, as the bolt start to unlock, it is rotated to unlock... due to much higher velocities with the carbine, the rotation of the bolt creates enough centrifical force to "float" the extractor... the extractor on the AR is not balanced and the forward part of it weighs more -- some argue that the pressure of the extracted cartridge case keeps the case head against the bolt face, but the fact is that the extractor does float and the contact with the case rim becomes "soft". For this reason, it is much more likely that the extractor will simply pop off, rather than actually rip the case.

Balanced extractors and different designs have been developed (LMT), but the best solution to date has been stronger extractor springs and spring buffers. That about covers the FTE issues...

Back to bolt velocity. The high speed of the bolt has a couple of other detrimental effects, one of the most common is that the bolt is cycled so fast that as it returns to battery, it actually has enough force to "bounce" off of the barrel extension when closing and locking... this bounce back is very small, but can be enough to cause the weapon not to fire... this "bolt bounce" is pretty well known.

One other problem is that the bolt can cycle so fast the magazine spring can not keep up with it and the round stack is not properly aligned and forced back into place before the bolt returns to batter -- therefore there is no new cartridge picked up and the bolt closes on an empty chamber, this is what some call "ghost loading", or bolt-over-base jams... this is far worse in full auto fire as the bolt does actually move faster in full auto than semi auto; this is due to the fact that the top cartridge in the magazine does not apply force to the bottom to the bolt causing drag.

The common solution to this issue is to use a stronger recoil spring and a heavier buffer... this works, but is treating the symptom, not the problem.

PigTail and expansion chamber gas tubes attempt to fool the rifle into thinking that the gas port is,  located further away that it really is, but they are not as good of a solution as actually moving the gas port out...

I guess that about covers it for a quick rundown, of course all of this is not nearly as simple as it sounds.

Quoted: Well, it is a good thing you came along later in the game I guess? The M4 had been around for almost 15 years by the time you started packing one and many of the issues already addressed... but this still does not change the fact that the system did/does have some concerns.

Well, before that I had a M16A2, and before that I was in the National Guard, and had an A1, got my first one of those in 1991 at age 18, but I do face something of an age handicap in having had one before that.

The system DOES have some concerns. Given as I'm constantly around a few hundred of the things in the hands of 19 year olds who don't read ARFCOM daily, I see what works and what doesn't.  I'd rate magazines and cleanliness the two biggest concerns with the M4 to keep it running. Then we get into lesser concerns found with introductory users like "rig your sling properly" and such.

Following that is "accept the limitations of the weapon and the cartridge", meaning M855 ball from a 14.5" barrel is not going to be a 500 meter Death Rifle no matter how hard some people may wish. When the rifle is employed properly, it works pretty well. I've seen what it does to people, and if you don't get a one shot stop, shoot the guy again. There's a reason we carry as many loaded magazines as we can get when we go out the gate.

The problems the original weapons may have had aren't any more relevant to what you'd buy new today than the problems of the 1965 M16 are. They are certainly of historical interest to people like us, but to the average shopper for a new production rifle, it's not that big a concern providing he buys a quality rifle and trains with it.

My .02

Quoted: In order to understand this, there are a few things about the functioning of the AR that have to be defined, I am away from most of my notes and stuff, so most of the figures given are from memory... but should be pretty close. For this description, the standard rifle gas system is with the gas port located at 9.5" and having a 20" barrel... the standard carbine system is with the port at 7.5" and a barrel of 14.5" The pressures at the gas ports are: 13.5K for the rifle and 26K for the carbine -- or twice as much. The dwell time (the time that the gas system is charged with high pressure) is determined by the amount of barrel after the gas port. These are nearly identical between the rifle and the carbine. Pressure from the port is regulated only by the size of the gas port and the diameter of the barrel. These two factors determine the internal bolt pressure, the maximum pressure that is obtained in the bolt carrier/piston combination -- for the rifle this pressure is about 1000psi and for the carbine it is over 1500psi, half again as much. When the rifle is fired, primer shot sets the bullet forward until it contacts the rifling, at this point the powder charge detonates and sets the shell case fully back, binds the action and start to propel the bullet. The bullet jumps slightly again and is etched by the rifling... it stops again very briefly as the pressures build to a point for the bullet to overcome the mechanical advantage of the rifling twist and the bullet starts to spin, at this point the chamber pressure is at max, 50K plus (there are some that believe there is another, third stop the bullet makes and some testing suggest this may be true). As the chamber pressures start to climb, the brass case expands and becomes plastic, this is essential to seal the case in the chamber -- the correct term for this is Obturation, when the case is obturated and sealed, it is stuck in the chamber, practically welded in really. The Lock Time, or the time that the action remains locked with no attempt to start unlocking is very important... on the rifle, the lock time is about 550 microseconds, the lock time for the carbine is about 375 microseconds -- this may not seem like much, but it is much shorter of a time, also keep mind that the chamber pressures are twice as high in the carbine when the unlocking starts. What does all of this mean? When the carbine is fired, the system attempts to unlock earlier than intended and while the case is still fully obfucated... this results in the action bind delaying the unlocking and stressing the system. As the 5.56N is not drastically tapered, "squirting" is not a big problem in most guns. When the internal bolt pressures finally unlock the bolt, the velocity of the reward movement in the carbine is much higher than what the rifle was designed for, it also must start extraction of the obfucated case... as you know, the AR does not have any sort of initial extraction, perhaps the single biggest shortcoming of the design. This has been known to cause ripped case heads... At this point, as the bolt start to unlock, it is rotated to unlock... due to much higher velocities with the carbine, the rotation of the bolt creates enough centrifical force to "float" the extractor... the extractor on the AR is not balanced and the forward part of it weighs more -- some argue that the pressure of the extracted cartridge case keeps the case head against the bolt face, but the fact is that the extractor does float and the contact with the case rim becomes "soft". For this reason, it is much more likely that the extractor will simply pop off, rather than actually rip the case. Balanced extractors and different designs have been developed (LMT), but the best solution to date has been stronger extractor springs and spring buffers. That about covers the FTE issues... Back to bolt velocity. The high speed of the bolt has a couple of other detrimental effects, one of the most common is that the bolt is cycled so fast that as it returns to battery, it actually has enough force to "bounce" off of the barrel extension when closing and locking... this bounce back is very small, but can be enough to cause the weapon not to fire... this "bolt bounce" is pretty well known. One other problem is that the bolt can cycle so fast the magazine spring can not keep up with it and the round stack is not properly aligned and forced back into place before the bolt returns to batter -- therefore there is no new cartridge picked up and the bolt closes on an empty chamber, this is what some call "ghost loading", or bolt-over-base jams... this is far worse in full auto fire as the bolt does actually move faster in full auto than semi auto; this is due to the fact that the top cartridge in the magazine does not apply force to the bottom to the bolt causing drag. The common solution to this issue is to use a stronger recoil spring and a heavier buffer... this works, but is treating the symptom, not the problem. PigTail and expansion chamber gas tubes attempt to fool the rifle into thinking that the gas port is,  located further away that it really is, but they are not as good of a solution as actually moving the gas port out... I guess that about covers it for a quick rundown, of course all of this is not nearly as simple as it sounds.

Very nice.  Thank you for your professionalism.

Quoted: Quoted: In order to understand this.... Very nice.  Thank you for your professionalism.

+1 great Info!

Quoted: While waiting for my wife to shop I picked up a Special Weapons magazine. It was saying the M4 is unreliable. Torn Case Heads, Failure to Extract ect. Being a Noob I want to know do these problems exist in say the Bushy M4 Types 14.5bbls? While I realize they are not the same animal I'm just wondering if these problems plague the civilian semi-auto versions as well? If someone could elaborate on this I would appreciate it! Thanks

Sounds like HK PR.  The last article I read like that was taken mostly verbatim from HK.

P.S.  I'm not disagreeing with Gunzilla's post.  I've read about those issues before.  

Quoted: In order to understand this, there are a few things about the functioning of the AR that have to be defined, I am away from most of my notes and stuff, so most of the figures given are from memory... but should be pretty close. For this description, the standard rifle gas system is with the gas port located at 9.5" and having a 20" barrel... the standard carbine system is with the port at 7.5" and a barrel of 14.5" The pressures at the gas ports are: 13.5K for the rifle and 26K for the carbine -- or twice as much. The dwell time (the time that the gas system is charged with high pressure) is determined by the amount of barrel after the gas port. These are nearly identical between the rifle and the carbine. Pressure from the port is regulated only by the size of the gas port and the diameter of the barrel. These two factors determine the internal bolt pressure, the maximum pressure that is obtained in the bolt carrier/piston combination -- for the rifle this pressure is about 1000psi and for the carbine it is over 1500psi, half again as much. When the rifle is fired, primer shot sets the bullet forward until it contacts the rifling, at this point the powder charge detonates and sets the shell case fully back, binds the action and start to propel the bullet. The bullet jumps slightly again and is etched by the rifling... it stops again very briefly as the pressures build to a point for the bullet to overcome the mechanical advantage of the rifling twist and the bullet starts to spin, at this point the chamber pressure is at max, 50K plus (there are some that believe there is another, third stop the bullet makes and some testing suggest this may be true). As the chamber pressures start to climb, the brass case expands and becomes plastic, this is essential to seal the case in the chamber -- the correct term for this is Obturation, when the case is obturated and sealed, it is stuck in the chamber, practically welded in really. The Lock Time, or the time that the action remains locked with no attempt to start unlocking is very important... on the rifle, the lock time is about 550 microseconds, the lock time for the carbine is about 375 microseconds -- this may not seem like much, but it is much shorter of a time, also keep mind that the chamber pressures are twice as high in the carbine when the unlocking starts. What does all of this mean? When the carbine is fired, the system attempts to unlock earlier than intended and while the case is still fully obfucated... this results in the action bind delaying the unlocking and stressing the system. As the 5.56N is not drastically tapered, "squirting" is not a big problem in most guns. When the internal bolt pressures finally unlock the bolt, the velocity of the reward movement in the carbine is much higher than what the rifle was designed for, it also must start extraction of the obfucated case... as you know, the AR does not have any sort of initial extraction, perhaps the single biggest shortcoming of the design. This has been known to cause ripped case heads... At this point, as the bolt start to unlock, it is rotated to unlock... due to much higher velocities with the carbine, the rotation of the bolt creates enough centrifical force to "float" the extractor... the extractor on the AR is not balanced and the forward part of it weighs more -- some argue that the pressure of the extracted cartridge case keeps the case head against the bolt face, but the fact is that the extractor does float and the contact with the case rim becomes "soft". For this reason, it is much more likely that the extractor will simply pop off, rather than actually rip the case. Balanced extractors and different designs have been developed (LMT), but the best solution to date has been stronger extractor springs and spring buffers. That about covers the FTE issues... Back to bolt velocity. The high speed of the bolt has a couple of other detrimental effects, one of the most common is that the bolt is cycled so fast that as it returns to battery, it actually has enough force to "bounce" off of the barrel extension when closing and locking... this bounce back is very small, but can be enough to cause the weapon not to fire... this "bolt bounce" is pretty well known. One other problem is that the bolt can cycle so fast the magazine spring can not keep up with it and the round stack is not properly aligned and forced back into place before the bolt returns to batter -- therefore there is no new cartridge picked up and the bolt closes on an empty chamber, this is what some call "ghost loading", or bolt-over-base jams... this is far worse in full auto fire as the bolt does actually move faster in full auto than semi auto; this is due to the fact that the top cartridge in the magazine does not apply force to the bottom to the bolt causing drag. The common solution to this issue is to use a stronger recoil spring and a heavier buffer... this works, but is treating the symptom, not the problem. PigTail and expansion chamber gas tubes attempt to fool the rifle into thinking that the gas port is,  located further away that it really is, but they are not as good of a solution as actually moving the gas port out... I guess that about covers it for a quick rundown, of course all of this is not nearly as simple as it sounds.

Great post, those numbers for lock time, internal bolt pressure, and gas port pressure all look about right to me, but have never seen them published before.  Do you have a source on any of that?

First off the M4/A1 Carbine is Standard A, meaning that deliveries are tested to meet Mil-Specs.  Acceptance includes lot testing of weapons for endurance testing.  The Mil-Specs for the M4 Carbines call for the same reliabilty as the Mil-Specs of full size rifles.  

However my experiance with M4 barrels (both USGI and commerically optained Colt's barrels) is that they are not at all as reliable as full size Standard A rifle barrels.  And I do mean the barrel, it is the 14.5" barrel that places the gas port closer to the chamber and thus results in the increased pressue in the gas system as desribed in detail by Gunzilla.

Specifically, I have had M4 barrels that run the bolt velocity at speeds that case the extractor to drop the fired case resulting in a failure to extract.  Also have one that runs fast enough that failures to feed occure.  My experiance has lead to me to fully test M4 barrels prior to doing anything with them, just plain won't trust one until tested.  This is unlike full size USGI rifles barrels, in which I have full confidence in, before firing a single round.

However, I do have M4 barrels that are proven dead reliable.  Some run, some don't, unlike like USGI rifle barrels.

Quoted: Do you have a source on any of that?

My secret laboritory... the floor littered with empty Mountain Dew cans, a fat bulldog and the corpses of rifles post necropsy. Really a very troubling sight

Wow. Great  information. Thanks for the  tech side of things, Gunzilla.

Gunzilla's post should be tacked somewhere because it answers a lot things that seemed to rehashed over and over again...

Quoted: I do have a correction to make though, like i've just said, the powder does not detonates but ignites.   HUNTER.

That is a rather important distinction.

Quoted: Quoted: Do you have a source on any of that? My secret laboritory... the floor littered with empty Mountain Dew cans, a fat bulldog and the corpses of rifles post necropsy. Really a very troubling sight

Any pics of that?

All that info is kinda like reading about how a baby is made. So many things have to go right it seems impossible that it would ever work. And yet....

Are we talking about only 14.5 barrels here. I mean true M4s.  How do 16 inch ARs fair?

Quoted: but they are not as good of a solution as actually moving the gas port out...

Hence, the reason for Mid-length uppers? (i.e. the solution to a carbine is a middy)

I was thinking that too but haven't seen anybody post anything where actual test and evaluation has been conducted with conclusive results.  

Quoted: I was thinking that too but haven't seen anybody post anything where actual test and evaluation has been conducted with conclusive results.

More info from recent thread on "reliability" Great reading to go along with GunRunners works

Quoted: Quoted: I was thinking that too but haven't seen anybody post anything where actual test and evaluation has been conducted with conclusive results.   More info from recent thread on "reliability" Great reading to go along with GunRunners works

Forgot all about that ArmaLite tech note.

I carry and M4 in the Army and I own a 14.5 inch barreld AR15 and I am no expert at all but I can say that I have never had a jam or any other problem in the M4 other than the hole in the back of the buffer tube is way too big and lets too much sand and dirt in it, that has been my only problem with it, when that tube is clean there is no problem on mine but if I can here dirt in it when I pull the charging handle back then I know it will not strip the first round out of the mag on a reload, after that tho it runs fine for me.

My friend on the other hand did have a jam, in a very bad time when we were in Iraq. We were going into a house at night and got caught in the fatal funnel because someone holding the door shut. Another individual ran to the close corner with a rifle and took sight, my friend shot two rounds, both missing, then his weapon jammed, I then handed him mine (mind you, we were stuck in the doorway, both of us, and I had no sight of the bad guy) and he then finished the job before the bad guy could get a round off.

Now both him and myself had fired countless number of rounds in Iraq without one single jam, ever, until that day, and none since. You just never know.

Oh, and his ACOG broke on him once over there too, maybe he just has bad luck with equipment.

Great Info!!!

Thanks!his?I don't know????? But it would seem that less pressures would mean slower times ect. Or is it not enough to make any real difference?

Quoted: I do have a correction to make though, like i've just said, the powder does not detonates but ignites.   HUNTER.

Sorry... big brain fart on my part

My background is largely in explosives/demo and I guess I get thinking in that explosive train mindset. Thanks for the catch

Quoted: Great Info!!! Thanks! Ok let me ask this? would the "problems" tend to be less with 223 ammo presssures than nato pressure ammos? I don't know????? But it would seem that less pressures would mean slower times ect. Or is it not enough to make any real difference?

I guess it would be slightly mitigated, but to any measurable effect? I doubt it... the rifle is pretty damn good like it is, problems identified and steps taken to reduce things as much as possible.

Quoted: I was thinking that too but haven't seen anybody post anything where actual test and evaluation has been conducted with conclusive results.

The middy gas system is a great way to take care of a lot of this... we made up a batch of midlength gas system M4s about three years ago and they were very pleasent to shoot... the first system was the Aardvark, with the gas block located in front of the FSB, simple, easy and worked well



This became the M4Ward... sorry, can't show you actual pics, but this is the line art drawing for the second to the final design, the current version is slightly different.


both Aardvark and M4Ward designs are owned and protected by Guerrilla Small Arms Research, have to say that...

Quoted: Any pics of that?

Nah... I am just a small time hack, nothing worth recording for history happens around here... plus, the goings on in the lab really are disturbing  

Quoted: At this point, as the bolt start to unlock, it is rotated to unlock... due to much higher velocities with the carbine, the rotation of the bolt creates enough centrifical force to "float" the extractor... the extractor on the AR is not balanced and the forward part of it weighs more -- some argue that the pressure of the extracted cartridge case keeps the case head against the bolt face, but the fact is that the extractor does float and the contact with the case rim becomes "soft". For this reason, it is much more likely that the extractor will simply pop off, rather than actually rip the case.

FWIW:  According to a Picatinny Arsenal presentation titled "Understanding Extractor Lift in the M16 Family of Weapons," extractor lift/floating occurs during the rearwards movement of the bolt, not during its rotation.  To prove their point, the researchers locked a bolt with a case under the extractor into a drill press, and cranked it up to 8,000+ rpm.  The extractor did not lift.  To further examine the theory of the rotational forces acting on an unbalanced exatractor, they replaced the extractor with one that had a large blob of extra metal welded to the forward end.  The test was repeated, and again no lifting was uncovered.

To prove their point about residulal chamber pressure holding the case head to the bolt face and the extractor lifting during the rearward movement, they put together a gymnasticator rig similiar to Tony Rumore's Siamese model.  The gas tube from Carbine A was fed into Carbine B's carrier key.  Four test were run.

Test 1: A live round was fired from Carbine B.  As Carbine B's carrier key was not met by Carbine B's own gas tube, the spent case was left in the chamber.  A live round was then fired from Carbine A.  The gas pressure fed from Carbine A cycled Carbine B's action, but failed to extract Carbine B's spent case.  

Test 2: The test was repeated again with the difference of an unfired case being placed in Carbine B.  As before, gas from Carbine A cycled Carbine B's action, but failed to extract the case.  

Test 3: The second test was repeated again, but this time the ejector was removed from Carbine B's bolt.  In this test, the case from Carbine B was finally extracted.  

Test 4: The third test was then repeated using a dinged case in Carbine B's chamber.  Unlike the previous test, the dinged case did not extract.

Another reason for the mid-length gas system. It does work.

Gunzilla, great stuff!  Details ARE very important-like TWICE the gas port pressure and just over half the lock time.  Those two factors conspire to make the M4 much more "finikey" than the M16.

Solution?  Many units in the sandbox have figured that absolute cleanliness is the best way to keep M4s AND M16s running well.  If anything like the fine dust there is in the chamber, there's more for the brass to "bite" on and provide more adhesion in the chamber.  If the upper has any dust in it it could slow down the action-but it's so much easier to keep the upper clean that this is not much of a problem.  Keeping the receiver extension tube clean and particularly the vent/drain hole clear helps a lot too; it's possible for the hole to vent as the carrier/spring/buffer go back, but not vent well as they go forward, slowing the feed portion of the cycle and leading to failure to strip or failure to fully chamber.  Crud is the rifleman's major enemy here, and strict and meticulous cleaning is the best weapon against crud.

Quoted: While waiting for my wife to shop I picked up a Special Weapons magazine. It was saying the M4 is unreliable. Torn Case Heads, Failure to Extract ect. Being a Noob I want to know do these problems exist in say the Bushy M4 Types 14.5bbls? While I realize they are not the same animal I'm just wondering if these problems plague the civilian semi-auto versions as well? If someone could elaborate on this I would appreciate it! Thanks

I'm sure someone has already chimed in as an owner but I'll add mine anyway. I own a Bushmaster M4A2 14.5", it(meaning mine) does not have said issues. In fact it has been my most reliable out of the 3 I own, even though my 20" was plauged with a full auto problems initially but Bushmaster fixed it.  It has probably 1200-1400 rnds through it since I bought in I think October of 2005, only problems were because of crappy magazines I used to prove a point to a friend.

Maybe they got a lemon from the factory, it happens, I got one. Mine has been reliable though, my favorite Ar of them all.

ETA: Great post Gunzilla, good information. Guess I am just fortunate so far, cause mine has been 100% to date with .223 or 5.56.

Quoted: Quoted: At this point, as the bolt start to unlock, it is rotated to unlock... due to much higher velocities with the carbine, the rotation of the bolt creates enough centrifical force to "float" the extractor... the extractor on the AR is not balanced and the forward part of it weighs more -- some argue that the pressure of the extracted cartridge case keeps the case head against the bolt face, but the fact is that the extractor does float and the contact with the case rim becomes "soft". For this reason, it is much more likely that the extractor will simply pop off, rather than actually rip the case. FWIW:  According to a Picatinny Arsenal presentation titled "Understanding Extractor Lift in the M16 Family of Weapons," extractor lift/floating occurs during the rearwards movement of the bolt, not during its rotation.  To prove their point, the researchers locked a bolt with a case under the extractor into a drill press, and cranked it up to 8,000+ rpm.  The extractor did not lift.  To further examine the theory of the rotational forces acting on an unbalanced exatractor, they replaced the extractor with one that had a large blob of extra metal welded to the forward end.  The test was repeated, and again no lifting was uncovered. Thanks! I do know about the test, and offer that what I described in no way contradicts this. As I said, the centrifical force floats the extractor by reducing some of the spring force... not saying that it lifts the extrator, but that it makes for a "soft" extractor engagement that is more likely to pop off of the case rim... I guess I could have stated that a little clearer, but I thought I got the point across? To prove their point about residulal chamber pressure holding the case head to the bolt face and the extractor lifting during the rearward movement, they put together a gymnasticator rig similiar to Tony Rumore's Siamese model.  The gas tube from Carbine A was fed into Carbine B's carrier key.  Four test were run. Test 1: A live round was fired from Carbine B.  As Carbine B's carrier key was not met by Carbine B's own gas tube, the spent case was left in the chamber.  A live round was then fired from Carbine A.  The gas pressure fed from Carbine A cycled Carbine B's action, but failed to extract Carbine B's spent case.   Test 2: The test was repeated again with the difference of an unfired case being placed in Carbine B.  As before, gas from Carbine A cycled Carbine B's action, but failed to extract the case.   Test 3: The second test was repeated again, but this time the ejector was removed from Carbine B's bolt.  In this test, the case from Carbine B was finally extracted.   Test 4: The third test was then repeated using a dinged case in Carbine B's chamber.  Unlike the previous test, the dinged case did not extract. Of course the residual chamber pressure is needed to properly extract the spent casing... as stated, if the rifle had initial extraction things would be soooooo much better! The testing you described above indicate that more than anything that the extractor setup is not capable of extracting a spent case that is held on the chamber by no more than the cantalever force of the ejector on the case and its own static weight... One has to point out the that this test could not dulicate the binding the action experiences as a result of full chamber pressure, but it does go to support the argument that if it can not extract a interference fit case, then trying to extract a a fully obturated case would be much harder?

Should they make M4 gas port even smaller?

Quoted: ... When the carbine is fired, the system attempts to unlock earlier than intended and while the case is still fully obfucated... this results in the action bind delaying the unlocking and stressing the system. As the 5.56N is not drastically tapered, "squirting" is not a big problem in most guns. When the internal bolt pressures finally unlock the bolt, the velocity of the reward movement in the carbine is much higher than what the rifle was designed for, it also must start extraction of the obfucated case... as you know, the AR does not have any sort of initial extraction, perhaps the single biggest shortcoming of the design. This has been known to cause ripped case heads... ... common solution to this issue is to use a stronger recoil spring and a heavier buffer... this works, but is treating the symptom, not the problem....

I was wondering if this description is not similar to that of the severe malfunctions encountered during the initial deployment of the xm16e1 in Vietnam during the 65-67 period. I read that these malfunctions stemmed from the Army's switch from the original IMR 4475 powder to the WC846 powder which caused an increase in the gas port pressure and created the same negative effects as described by Gunzilla in his post (of course here the problem was made more severe by the increased fouling properties of the new powder as well as the lack of a chromed chamber).

I read a similar description here:
The saga of the M16 in Vietnam

Quoted: Should they make M4 gas port even smaller?

Was tried, leads to more malfunctions, especially in cold environments.

Would the M4 be less prone to failure with underpowered rounds like wolf?

Quoted: Quoted: ... When the carbine is fired, the system attempts to unlock earlier than intended and while the case is still fully obfucated... this results in the action bind delaying the unlocking and stressing the system. As the 5.56N is not drastically tapered, "squirting" is not a big problem in most guns. When the internal bolt pressures finally unlock the bolt, the velocity of the reward movement in the carbine is much higher than what the rifle was designed for, it also must start extraction of the obfucated case... as you know, the AR does not have any sort of initial extraction, perhaps the single biggest shortcoming of the design. This has been known to cause ripped case heads... ... common solution to this issue is to use a stronger recoil spring and a heavier buffer... this works, but is treating the symptom, not the problem.... I was wondering if this description is not similar to that of the severe malfunctions encountered during the initial deployment of the xm16e1 in Vietnam during the 65-67 period. I read that these malfunctions stemmed from the Army's switch from the original IMR 4475 powder to the WC846 powder which caused an increase in the gas port pressure and created the same negative effects as described by Gunzilla in his post (of course here the problem was made more severe by the increased fouling properties of the new powder as well as the lack of a chromed chamber). I read a similar description here: The saga of the M16 in Vietnam

Yes, there is a bit of deja vu here, in regards to port pressure, in that the switch to ball powder, and moving the gas port back both resulted in increased port pressure.  The thing is that moving the port increased port pressure close to 100 percent, while the switch to ball powder resulted in a small increase.  The two gas problems are not close to being in the same league.

The most serious complaint against the XM16E1 was that fired cases would stick in the chamber, and had to be removed by ramming a cleaning rod down the bore.  This is a complaint I have not heard or seen in a M4/A1 Carbine.