Cause of AR unreliability?

[Webster-dl]

A clarification: I am not saying ARs are unreliable. Rather, I hope to ask: in ARs that have become unreliable, what is the primary cause?

The Big M4 Myth: ?Fouling caused by the direct impingement gas system makes the M4/M4A1 Carbine unreliable.? | DefenseReview.com (DR): An online tactical technology and military defense technology magazine with particular focus on the latest and grea

Http://www.luckygunner.com/labs/brass-vs-steel-cased-ammo/

I think that the impression I get between these two articles is that ARs, surprisingly, don't become unreliable from dirtiness and failure to clean. Rather, the failures to cycle in ARs that are built well and have not experienced outright components breakage or magazine problems is primarily from failure of the gas system. It seems that most of the unreliability is related to the gas system clogging off due tonrust or carbonization, and therefore insufficient gas being delivered to the bolt to cycle it. In this case, the most reliable ARs would seem to be the ones with the largest gas ports/tubes, as this would ensure the least susceptibility to carbonization induced gas tube obstruction.

Take home message (if this is true):
1) don't worry about cleaning the AR so much. In fact, cleaning the barrel can maybe even wait until accuracy falls off. After all, overzealous cleaning of the barrel can result in damage to the crown, chamber or rifling.
2) Get rifle length gas tube
3) get appropriate recoil buffer
4) keep bolt well lubricated (though not necessarily clean...well lubricated).

What do you guys think? I haven't followed any of these rules myself...but I don't shoot enough to clearly see the difference.

 

[Webster-dl]

Oh...corollary. What if, in Vietnam, the problem wasn't failure to clean, per se. What if the problem was that in failing to clean the gun, the soot and powder residue, in combination with the tropical Vietnam humidity, accelerated corrosion of the gas tubes in the M16 causing failure? What if it wasn't simply an issue of being "too dirty" afterall? BTW...does anyone know if the US was using corrosive primers in Vietnam? I know (or at least heard) many militaries, including our own at one time, favored corrosive primers because of their long shelf life and stability.

 

[jblomenberg16]

I would tend to agree... a lot of the malfunctions I've seen and had have been either gas system or magazine related. I've been trying to tune a load for my 300BLK SBR, and have pushed my reloads to the limits of gas pressure to get just enough to cycle yet stay subsonic. When the gas pressure drops low enough, cycling becomes very temperamental in most DI AR's. There are tons of posts about over / under gas'ed AR's out there and mismatched buffers to go with it.

Mag issues are the same way...sometimes a bad follower or spring either presents the rounds too low and thus gets a fail to feed, or sometime pops out two rounds at a time and you get double feed.

 

[Vespid_Wasp]

Your entire premise is flawed. AR's don't 'become unreliable'. They are largely reliable to a fault even when fed **** ammo that is underpowered and comprised of a non-ideal case component.

Buy an AR. Buy decent mags. Pmags, Lancer, USGI from D&H... Feed it decent ammo. Enjoy better accuracy, better ergonomics, better modularity, better reliability, and better optics mounting than that hunk of **** AK that belongs in a garbage can.


Put some oil on it every once in a while. Clean it once a year if you want. As long as it has some oil on this shiny spots, it will run and run and run.

 

[prescut]

No, Vespid_Wasp, tell us how you really feel about AK's.

 

[Webster-dl]

To be clear: I am not saying all ARs become unreliable inevitably. The first article made mention that even military m4s maintained by Army armorers malfunctioned and became unreliable in use. His conclusion was that it was not because of "dirtiness" but because of gas system issues which he corrected with springs and buffer adjustment (and a little oil).

The second article mentioned that in some ARs that failed the testing, it was because of gas tube failure (accelerated by dirty ammo), not dirty bolts or chambers causing malfunctions/incomplete cycling.

So...it would appear that the root of many malfunctions/unreliability in the AR is not dirty bolts/chambers/barrels but corroding/obstructing gas systems...so keep your gas system/recoil spring/buffer in good/balanced condition and your gun should function despite a dirty chamber or bolt.

 

[Webster-dl]

Could it be related:
Carbine length gas port size : 0.072
Rifle length gas port size: 0.100
AKM (7.62x39) gas port size: 0.15 to 0.177 in a carbine length barrel
?

Not that AKs are "better designed"...that is not what I am saying. I am just saying that maybe the whole piston vs DI argument is misguided...maybe it's all about port size and gas system "health" and the ARs with bigger ports tend to be more reliable? If somewhat overgassed?

 

[rob63]

Oh...corollary. What if, in Vietnam, the problem wasn't failure to clean, per se. What if the problem was that in failing to clean the gun, the soot and powder residue, in combination with the tropical Vietnam humidity, accelerated corrosion of the gas tubes in the M16 causing failure? What if it wasn't simply an issue of being "too dirty" afterall? BTW...does anyone know if the US was using corrosive primers in Vietnam? I know (or at least heard) many militaries, including our own at one time, favored corrosive primers because of their long shelf life and stability.

According to an article in the American Rifleman written by E.H. Harrison the issue was traced to an excessive amount of calcium carbonate added to a few lots of propellents made prior to 1968. The calcium carbonate was added to eliminate any excess acidity left over from the manufacturing process, but it caused excessive fouling of the gas tube. The article is based upon Frankford Arsenal Report R-1936, Aug. 1968.

 

[Fargo]

Could it be related:
Carbine length gas port size : 0.072
Rifle length gas port size: 0.100
AKM (7.62x39) gas port size: 0.15 to 0.177 in a carbine length barrel
?

Not that AKs are "better designed"...that is not what I am saying. I am just saying that maybe the whole piston vs DI argument is misguided...maybe it's all about port size and gas system "health" and the ARs with bigger ports tend to be more reliable? If somewhat overgassed?

Overgassing an AR leads to its own reliability problems, particularly in full auto. It also is hell on the extractor and can deposit more brass shavings in you action/FCG than the gun will like.

The m16/ar15 NEEDS some delay in the action both for the case to free from the sides of the chamber and for a m16 to chamber a new round before the hammer falls. Severe enough overgassing leads to mangled brass and hammer follow in FA.

Pistons are more forgiving of gas issues simply because they are a far simpler system. Impingement guns are requiring compressable gas to keep doing things way further down the line whereas pistons guns have direct mechanical parts take over much earlier.

 

[rob63]

Interesting questions and good observations!

Another thought that I have had, based on my own observations. If you pull the bolt back as far as it will go on an AR-15 you find that the maximum amount of travel possible behind the rear of the magazine is roughly 3/8". That is an eyeball estimate, I haven't measured it. If you do the same with an AK-47 it is more like 3/4". That means that the AK system can begin short-stroking and can probably remain operational since it was over-traveling in the first place. It only makes sense that with an over-gassed system you would also have the bolt travel an extra distance as well and that the combination would lead to greater reliability. I may be all wet, it wouldn't be the first time, but it would be interesting to see somebody study all of this.

 

[seedubs1]

Also remember, if you go with a bigger gas port and longer cork time (aka "over gassed"), you're pumping (and depositing) more combustion products through your gun (and gas system). That's a recipe for issues as well.

It's not just:
Increase gas port and cork time to get more force on the bolt for more reliable cycling.

It's:
Increased gas port and cork time dumps more crap in your gun and wears out components faster while initially giving you more margin on the force balance. And it's why you need a bigger buffer for over gassed guns. It's all about balance.

Optimally, I'd prefer to optimize the gas port and cork length so that you can run a carbine buffer as the largest buffer that will result in reliable cycling with my least powerful round. This way, you're dumping the least combustion gas through the gun and your bolt cycling is the least jarring on your components.

 

[Webster-dl]

According to an article in the American Rifleman written by E.H. Harrison the issue was traced to an excessive amount of calcium carbonate added to a few lots of propellents made prior to 1968. The calcium carbonate was added to eliminate any excess acidity left over from the manufacturing process, but it caused excessive fouling of the gas tube. The article is based upon Frankford Arsenal Report R-1936, Aug. 1968.

So that WAS it! It wasn't dirty chambers, bolts or barrels. As far as I know, the gas tube isn't really practical to clean, maybe just the gas block.

 

[rvb]

It seems that most of the unreliability is related to the gas system clogging off due tonrust or carbonization, and therefore insufficient gas being delivered to the bolt to cycle it.

Not sure how that was your take-away. The first article never even mentioned the gas tube or gas system clogging. The second mentioned it in regards to the crap ammo only. The first article was really more about buffers and action springs.

crap mags, crap ammo, and not enough lube are the biggest causes of problems in ARs. clogged gas system is WAY down on the list. Most people would be shocked at the reliability of ARs made with good components (eg not bargain-bin barrels w/ crap-cut chambers)

I've gone several thousand rounds (4-5k) w/o cleaning before. I just make sure it's well lubed and go shoot. Bolt and carrier need well lubed (lugs, carrier raceways, cam pin, rings).

rifle gas somewhat helps. I'm also a big fan of the new A5 recoil system... rifle action spring in an adjustable stock.

-rvb

 

[rvb]

So that WAS it! It wasn't dirty chambers, bolts or barrels. As far as I know, the gas tube isn't really practical to clean, maybe just the gas block.

crap mags, crap ammo, and not enough lube are the biggest causes of problems

The Army used crap ammo (incorrect powder, actually), despite the recommendations from the rifle manufacturer. With good ammo, this is not a concern.

-rvb

 

[cosermann]

If an AR has "become" unreliable, I'd check to see if the gas key has loosened. The gas key bolts in many mid to lower end ARs are not properly staked. Ejectors, extractors, and mags should also be checked. Parts wear out.

With respect to the Vietnam issue, there were lots of factors that needed tweaking to fix the system. Which factor or what combination was the main cause is debatable.

Here are a few: the .gov changed the powder with which the cartridges were loaded (yes, this was political, and involved contracts) without adequate testing, there was a belief by some that the rifle was "self-cleaning," there was a decision not to chrome the chamber in the early production rifles, and cleaning kits were often not issued. Personally, I don't think there was a good understanding early on as to how dry or wet to run the system. My tendency is to think the lack of chrome lining was the chief culprit, but no "experiments" to identify a single cause were ever done as far as I know. From what I've heard, the above issues were corrected within 2 years, however this was with new production rifles and ammo. I have not heard that the originals were ever retrofitted.

Most weapon systems have early teething issues. Even the M1 Garand was not immune.

Today, the AR a very reliable system.

the reliability of the M16 in Vietnam - AR15.COM

 

[M67]

Most weapon systems have early teething issues. Even the M1 Garand was not immune.

HOW DARE YOU!!! THE GARAND AND M14 WERE RIFLE PERFECTION FROM DAY 1!!!!

ARs to me have been extremely reliable. I grew up and still hear how ARs are unreliable and must be cleaned every 10rds or they won't work (same people who say revolvers never break). So when I started buying and building ARs for myself, I wanted to test them and I never clean mine, I just squirt some new lube in there every 800 rounds or so and they keep on shooting and get smoother and smoother.

Every rifle is man made and if one of those parts break, wear out, etc. the system will not work. Same with a lot of pieces of machinery.

I've had a couple stoppages in one of my ARs, but it's because I have a 20rd PMAG that only likes 19rds. I've had more issues out of AKs than ARs (AKs were mag related too)

 

[Mr Evilwrench]

It was my understanding, though it may be apocryphal, that the early problems were due largely to incorrect powder. They were manufacturing the 5.56 rounds (M193) with powder recovered from WWII surplus 30-06 rounds. This powder didn't burn right for the direct impingement M16, and caused much fouling. Once that was addressed, and the barrels chrome lined (the jungle is hard on firearms), most of the trouble had been addressed.

 

[rob63]

The article I mentioned earlier covered the "incorrect powder" story that has been around for many years. The Frankford Arsenal investigation found that it was a myth. There was absolutely no difference in performance between ball powder and extruded powder, the problem was the calcium carbonate content.

 

[Mr Evilwrench]

So, it wasn't so much the form of the powder as the recipe, then?

 

[rvb]

So, it wasn't so much the form of the powder as the recipe, then?

right. I've put thousands of rounds down the pipe w/ ball powder (H335).

-rvb