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Posted: 12/15/2004 9:15:30 AM EDT
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Does the M16A2 have the same problems with overheating and barrel failure as the m4? Does length have anything to do with it? How? I'm referring to the phenomenon detailed in this thread M4 fire to failure which was also talked about in Black Rifle II, in the discussion of why SOCOM went to the Heavy Barrel after expereince in Afghanistan. There is no talk of a similar problem in the 20" barrels, so I'm wondering if this is a problem specific to short barrels. |
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The M16A2 will overheat quicker and the barrel with fail sooner than the M4 barrel. These weapons are NOT intended to be SAWs - treat them as such and the barrels will burst. Does length have anything to do with it? I'll bet the combination of length and weight do factor in causeing the barrel to bend quicker and to a greater degree. |
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From the first sight, the M4A1 SOPMOD is an ideal Special Operations weapon - handy, flexible, with good firepower. But the latest experience in the Afghanistan showed that the M4 has some flaws. First of all, the shorter barrel commands the lower bullet velocities, and this significantly decreased the effective range of the 5.56mm bullet. Second, the M4 barrel and the forend rapidly overheats. Third, the shortened barrel resulted in the shortened gas system, which works under greater pressures, than in M16A2 rifle. This increases the rate of fire and produces more stress on the moving parts, decreasing the reliability. when you add to the stopping power situation the fact that the M4 tends to overheat and malfunction when run extensively on full auto, the picture starts getting even bleaker. Apparently, as the M4 gets hot, it eventually blows its gas rings, and can even fire rounds literally out of the side of the barrel. The barrel problem occurs when, while firing on full auto, the barrel begins to bend and vibrate under the intense heat that builds up. A joke it is not. |
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From Armalite: Tech Note August 24, 2003 Technical Note 48, The Effects of Barrel Design and Heat on Reliability Background: The M4 Carbine has developed a reputation for poor reliability. The excessive malfunction rate of the M4 Carbine is due to physical imbalances in the mechanism itself, exacerbated by heat. Analysis of the problem requires a good understanding of the carrier group and barrel of the rifle, and the functions of the cartridge case. Facts: Relation of carrier group design, barrel length, gas port location, and propellant gas pressure. The distance from the chamber to the gas port, the length of barrel beyond the port, and the pressure of the propellant gasses determine the amount of energy provided to the action of the M-16 series rifle. The heart of the M-16 operating system, the carrier group, was designed to function well with the original 20 inch long barrel of that rifle. The carrier group and the location of the gas port were carefully balanced to provide outstanding reliability with the ammunition that was designed for the M16. A change in the cartridge (bullet weight or powder), the length of the barrel, or the location of the gas port along the barrel can substantially change the pulse of gas that enters the carrier group and drives the rifle action. Short versions of the M16 (including the M4) suffer from relocation of the gas port and changes in barrel length. (note: The timeline of the government-generated chart above is measured in millionths of a second) The carbine gas port is located closer to the chamber than the gas port of the rifle: 7.5 inches instead of the 13 inch distance on the rifle. The gas pulse therefore enters the gas tube sooner and reaches the carrier group earlier than it does in the rifle length barrel. In addition to reaching the carrier sooner, it reaches it at higher pressure. The gas pressure at the carbine’s gas port is double that of the rifle: 26,000 psi vs. 13,000 pounds per square inch. The early pressurization of the carrier causes the carbine to begin to extract earlier than the rifle does. At the same time, the gas in the carbine’s carrier is of higher pressure than it is in the rifle, and it forces the carrier to move the rear at a higher velocity than it moves in the rifle. Because of the earlier extraction, the cartridge case has less time to transfer heat to the chamber wall and shrink away from it before extraction begins. The cartridge case has a tendency to stick to the chamber wall, and resistance to rearward movement is high. When the bolt, drawn rearward by the high velocity bolt carrier, tries to pull this stuck case to the rear, both the extractor and cartridge case are heavily stressed. The resistance can cause the whole mechanism to become sluggish or stop, or to cause early failure of the extractor or bolt. As discussed above, the distance from the chamber to the gas port is important. So too is the length of the barrel past the gas port. That’s because the bullet serves as a plug to keep the gas pressure trapped in the barrel so that some of it can pass into the gas tube and back to the carrier. If the length of barrel beyond the gas port is too short, so is the “dwell” of the plug in the barrel. The gas pulse supplied to the carrier can be too short to deliver all of the energy that the carrier group needs. Too long a section of barrel beyond the gas port can cause too long a gas pulse. Carbines with 11.5 inch long barrels have a very short segment of barrel beyond the gas port and the gas pulse is thus shorter than the carrier group requires. This problem combines with the carbine problems already described, and the reliability of carbines with 11.5 inch long barrels is somewhat poorer than carbines with longer barrels. Efforts to adjust for the short barrel by enlarging the gas port produce a firearm that is extremely sensitive to differences in ammunition. Efforts to correct the problem by using different springs or buffers or by changing the volume of the gas used are only partially successful. The faster movement of the carrier group in carbines also creates an interesting and largely unknown problem with the extractor. During extraction, the extractor opens for a very short period, and then recovers to complete extraction. The faster movement of the carbine bolt increase the time that the extractor is open. This tends to decrease extractor efficiency and increase extraction trouble. Correcting basic carbine weaknesses: 1. Reduce the diameter of the gas port to reduce high pressure gas flow to the carrier. This can render the mechanism somewhat more prone to powering problems than the larger gas port of the rifle. 2. Provide an expansion chamber to buffer the gas flow and/or store gas to power the carrier. Such chambers tend to cool the gasses and can become clogged with powder residue over time, reducing the buffer effect. The flash hider of the Vietnam-era XM177 Carbine provided a buffer effect and stored gas. 3. Shift the gas port. ArmaLite has shifted its carbines gas port two inches forward compared to the M4 Carbine. Since the commercial minimum barrel length is set by law, this change serves reduce the gas pressure, delay its transmission to the carrier group, and reduces the length of barrel (and thus gas pulse duration) beyond the gas port. This change is easy in a commercial setting but has logistics implications for the military. 4. Decrease the tendency of the extractor to open by increasing extractor spring strength, adding material to rear of the extractor to reduce the tendency to open, or adding various elastomer forms to the extractor to reinforce the spring. Effect of heat on firearm function. Heat increases the carbine problems listed above. Understanding the effect of heat requires a firm understanding of the purpose and action of a component of the rifle system that is often overlooked: the cartridge case. The cartridge case is a highly sophisticated component that performs a number of functions 1. It holds components (bullet, primer, powder) together precisely. 2. It engages key surfaces of the magazine and rifle to transport these components into the chamber. 3. Upon firing, it expands into intimate contact with the chamber wall to seal high pressure gas in the barrel. 4. It contracts from the chamber wall when pressures lower to an acceptable level and when some of the heat within the case is transferred to the chamber wall. 5. It transports heat out of the weapon when extracted. When the weapon overheats, it is harder for the cartridge case to transfer heat to the hot chamber wall and shrink away from it. Adhesion of the cartridge case to the chamber wall results in increased resistance to extraction. Heat affects carbines worse than it does rifles because of their earlier extraction Effect of heat on the barrel. In addition to increasing the malfunction rate, excess heat weakens the material of the barrel. The barrel of the M4 carbine is made of chrome-molybdenum-vanadium steel, and is chrome lined. It is a high quality grade of steel capable of long service. This steel tolerates high temperature well. At a temperature of approximately 1100 degrees, however, the structure of this alloy undergoes a permanent transformation that substantially, and permanently, alters it. The steel becomes prone to rupture under high pressure. It may not fail at the time of overheating, but instead may fail at a later date and far lower temperature. This confuses the user as to the reason for failure Eliminating barrel failure. 1. Efforts to reduce barrel failure have centered around tests of different materials or coatings, adding mass to serve as a heat sink, and providing other features like cooling fins or water jackets to cool the barrel. All of these techniques provide either little benefit or result in serious disadvantages like increased weight and cost. 2. There is a private effort underway to avoid heat by designing ammunition that will not put it into the barrel in the first place. This effort is in its early stages and, even if successful, would not result in a change to service ammunition for some years to come. Summary: Problems with the M4 and other carbines and some commercial rifles based on the M16 design are more subtle than they appear. Changes to the hardware or ammunition can improve firearm performance, and research into the dynamics of the M4 are pointing the way to improvements. Additional benefit can be obtained by operator discipline in maintenance (lubrication) and controlling heat. Overheating is an especially crucial issue in M4 Carbine reliability and in barrel failure in all models. Most importantly, carbine users must remember that there is no free ride: the advantages of short barrel length come at the expense of increased sensitivity to differences in ammunition. Carbine users MUST test and select ammunition that works well in their short-barreled arms instead of purchasing based on price alone. Regardless of the rate of fire a Soldier or Police Officer wishes to shoot, the designs and materials available require control of the firing rate except in the most critical circumstances. The potential of damage from overheating thus combines with the general need for ammunition conservation and accurate fire to force users, regardless of instinct, to lower their firing rates. In the final analysis, tactics must bend to a number of influences, among which is physics. MARK A. WESTROM President Copyright 2004 ArmaLite Inc. All Rights Reserved |
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There was a public military report regarding how many rounds an M4 could fire before the barrel ruptured. I can't find the link anymore - does anyone else have it? From memory, the barrel would rupture approx 4-8" from the receiver after several hundred rounds fire nonstop full auto. -z |
Keep in mind that Armalite produces rifles using basically the same gas systems and other components and will face the same technical challenges. Are you suggesting the prancing pony is a magical talisman against the laws of physics? |
Look here: M4 failure |
No, I think he's suggesting that Armalite has their own problems that they can't resolve. Kinda like the designer of the Pinto commenting on how to fix design flaws in a Corvair. |
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Thanks No1Home, that was a highly informative analysis from Armalite. Interesting that someone would think that COlt not only has proprietary rights to the best carbine or the military contract, but that they also have proprietary rights to an understanding of the physics of firearms function It made sense to me. I'm filing it away, regardless of the author. |
Yes - in fact the M16A2 has a worse problem. I'm sure length does have to do with it - more droop to the barrel sooner and you get ruptures.
I don't know where you are getting your info - but the Army put in for the heavy barrels for the M4A1s in Fiscal Year 2001 (which started 01 Oct 2000) - well before the 9-11 attack and our guys going into Afghanistan. There were tests done years prior - consult the FULL document you reference you'll see training incidents going back to the mid/late 1990s.
No it's not specific to short barrels, nobody talks about M16A2 problems because nobody is trying to use M16A2s like SAWs. The M4s & M4A1s were being abused with higher rates of fire than the carbines were designed for - much like a short SAW - so the problem was noticed with them. When the Rock Island started receiving complaints they looked into the matter (again reference the original barrel test) and through testing found the problem was worse with the M16A2. It turns out it wasn't an equipment problem - it was an operator problem. The operator's were abusing the weapons well beyond their design specs. |
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Thanks Forrest. BR II just says that the problems encountered in Afghanistan were attributed to desert heat and heavy cover fire in Ranger units. I'm sure it's not the whole story, it's just the part of the story that was told in the book. If you haven't seen the book, I highly recommend it, it's a good read. SOA |
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There was a version of the C-7 with a carry handle and vertical foregrip and heavy bull barrel that was intended to replace the C-2 (heavy barreled FAL) We got minimi's instead. I don't know if it was a technical failure though. If someone put a heavy chrome lined barrel (like bushy sells) on a F.A. rifle I see no reason why it couldn't sustain a higher rate of fire than the pencil barrel. I think the canadian support version was scrapped because of belt vs. mag feed IIRC. My question it, couldn't a bull barreled Ar with bipod ect. sustain fire much like a saw? (heck the barrel is about as thick or thicker than the minimi's I've seen anyway) |
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you mean like this one? Colt LMG I wonder the same thing... That thing looks like a Sombitch, don't it? |
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Ours looked like that except for the obligitory A1 rear sight. I was thinking lately of building a "saw" using a heavy barrel, vertical foregrip, Ycomp (cause it looke "neet" as the wifey says) hook buttstock with hinged buttplate (I'll have to make that, no biggie though) and bipod attatched to the forward part of the handgaurd. Anybody got any ideas if it could be a suitable poor man's "saw" or version of the colt LMG or would I just be better off with a rifle version? (take off the do-dads and it is anyway) Does anybody use the colt LMG?? |
Colt OWNS the rights and all the exact tech data on the M4. Colt and the military knows it. Armalite wants to tell me in the write up, how bad a Colt M4 is when used in a fashion it was never meant for.  It's like someone who owns a Ford Ranchero writing up a paper on the Chevrolet EL Camino, and telling them how bad of a car it is because the motor blows up after trying to make it rev to 10,000 rpm for an hour. Would you take that to heart?  |
I agree partially with the statement that theirr is "no free ride" but only when it comes to sustained rapid fire. This failure problem is not with the M-4 which is what the majority of troops are issued (safe/semi/burst) but with the safe/semi/full of the M4A1 for Rangers/SF community, Ya just can't expect a light weight carbine with a small diameter barrel to be able to sustain constant mag dumps of covering fire/break contact scenarios. I doubt the SCAR light will fair much better. and realistically what are we really talking as far as shear numbers of failures????. The Military SF community has been using a CAR derivitive of the M-4 since the 60's, and now all of a sudden it's a big problem!!! 596 rds fired in 3.5 mins is pretty extreme in my book and very few 'Operators" are ever going to reach that extreme under any circumstance other then breaking contact against a bde on the surface of the sun!!!! 
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For the increased bolt wear I found this thing over in the ARFcom reviews. supposedly it cuts down gas pressures for carbine length AR's http://www.ar15.com/content/products/accessories/gasTube something the SF might wanna look into if they continue to have problems my .02 |
The Danes do IIRC. BTW just after the 94 ban went into effect one of the AR custom shops bought a whole buch of the Colt LMG uppers and was selling them (at a hefty price) often with a combo visible/IR laser attached. There was an article on them about 9-10 years ago in the old 'Survial' magazine. Would have made a neat collectors item (the LMG upper) but I don't see a practical purpose - an HBAR with a DD12.0 or Troy MRF-R will do the same thing - only better. |
IIRC the heavy barrels bushmaster sells are thicker than the saw barrels. I wonder how well the two would stack up against each other as far as full auto sustained fire goes. I think I will build that heavy "squad auto" version just for fun. I like the idea anyway, parts compatibility and magazine compatibility (I know, the saw can take stanag mags too, but it ruins them every time and I aint got the budget for an M249 )Anybody know for sure the comparison of profiles between bushies HBAR profile and a "saw's"? |
If your conclusion is based entirely on the document referred to in the other thread, do you really consider that testing 1 M4 barrel against 1 M16A2 barrel allows such a generalization? |
Hell if you fire that much to kill a rifle barrel, you need a belt fed weapon. Even then you arent safe. I killed an M60 barrel. we linked up about 150 tracers and burned em through. Probably got about 95+ before the barrel had a scary glow to it. That thing keyholed rounds after that. and yes this deserves a 
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Actually it was 2 M4 barrels/. But yes I do. The barrels are all of consistant diameter & material (they already passed their accpetance testing). They should all perform pretty much the same. The barrels were then tested afterward to make sure failure wasn't due to a flaw in the barrel. Since no flaw was found it can be reasonably assumed that you will get consistant results among 'in spec' barrels. |
| ArmsTech uses a gas trap system to regulate pressure to carrier. Was written up very favorably a couple of months ago in a Mil/LEO publication. Use of the gas trap cut cyclic rates down 100-200 rpm from a stock M4; also allowed use of mags that wouldn't feed reliably in an M4. Just some snippets, but the idea did sound cool. They also utilized polygonal, gain-twist rifling. A 10.5" ArmTech barrel produced the same velocity as a brand new 14.5" M4 barrel. |
Explain to me how a gas regulator has anything to do with making a shitty magazine work in a rifle? |
I had the EXACT same idea! I never went through with it though; I live in California and only have three lowers...and half a dozen upper configurations already! For the buttstock, I was thinking about the Choate "hooked" buttstock that BM sells... Still, I'd like to see someone pick up the ball and run with it... |
[Q] It's quite simple really. Magazines with main springs that have become weaker take longer to feed the next round up. If the carbine is cycling fast (as M4s do) then they can cycle before the round has had time to get 'into place'. By slowing down the cycle time it gives the magazine more time to get the round into position to be properly fed into the chamber. Thus making marginal magazines (ones that work in say M16A2s but not M4s) work perfectly again. [/Q] Of course you can also fix those same magazines with a Wolf 10% extra magazine spring. |
Dude, you're banging your head against the wall in the forum with trying to explain the problems of the M4 because some people have rocks in their skull and nothing sinks in. Here is the biggest problem the M4 has: It was never intended to be a full fledged combat rifle. It was intended for support units who needed something better than sub guns and pistols, and vehicle operators who dont have much space. The other use was for a light agile weapon for special operations and recon units. So what happened? Some people started confusing the M4 with a real combat rifle, but the M4 lacks the range, power and durability for sustained fighting. The short profiled barrel wasnt supposed to be seeing long periods of sustained fighting the way the M16 was. The long M16 barrel can better evenly dissapate hit due to the greater surface area despite also being profiled. Once the M4 stepped out of its comfort zone is where things went wrong and a great mission specific weapon become an inefficient carbine that never has and never will perform as good as the M16A4. Now I wait for the, "but it's short", "combat is only 50 yards", "...but with 77gr bullets...", "fragmentation isnt that important", blah blah blah. Still doesnt perform as well as the M16A4 as a primary combat rifle. Flame suit on. I've heard it all before. Bring it 
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I don't buy it. All the presumption and reassurance in the world makes no difference to the results of an experiment. It just seems lazy and unscientific to rest a conclusion on such a tiny sample size. |
Exactly. The other thing he quoted was M4 cycling rates increase with round counts, up to close to 1,000 rpm. What causes that -- worn gas rings, worn recoil springs, or was he wrong in making that statement? |
Worn Gas port. Which is a bigger problem for carbines than rifles (because there is lower pressure at the port on a rifle). This is pretty much the issue Armalite was discussing in their brief. |
That is what I would think too; but the experiment referenced above shows that not only did the M16A2 barrel fail first, it also got hotter faster than an M4A1 barrel subjected to the same treatment. The A2 barrel reaches 1400 degrees in about 9 mags. The M4A1 takes about 12-13 mags to hit the same temperature despite having less mass. |
Mid-lengths on 16" barrels are sounding smarter and smarter. |
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