Marginal aspects of AR design.

[bsmithwins]

Without trying to irritate anyone by picking on their favorite rifle, it seems like a lot of aspects of the AR's basic design are marginal:

1) The bolt is over stressed for the specified steel. Either a better grade of steel should have been specced, more generous stress relief cuts should have been used, or the locking lugs by the extractor should have been beefed up. Or all three. Alternately, a larger bolt could have been used, which would allow for more steel in the highly stressed areas and better stress relieving features.

2) The cam pin hole in the bolt causes a stress riser. This should have been eliminated. However, with the current design making the cam pin hole in the extractor smaller forces the cam pin to be smaller, which might lead to cam pin breakages.

3) Extraction is marginal. More spring force is needed and/or a widerextractor would provide for more of a margin against failure to extract.

4) Bolt travel is too short. As is, the bolt travels just enough to pick up the next round. Anything that interferes with the bolt's travel results in short stroking. A design that allowed bolt over travel would provide a margin against short stroking.

5) Debris* mitigation features are lacking. The AR has lots of tightly fitted parts with minimal clearance between them. Sand cuts should have been provided like the FAL and/or minimize contact areas of the bolt carrier, and receiver, like the G3, AK, and SCAR designs do. You could even do self clearing features like the Stirling SMG had. A automatic ejection port door like the FNC would be a nice feature too. Anything that relies on the operator is asking for trouble.

The trouble is no one can try and fix any of the problem areas without breaking the modularity/interchangeability of the AR. Design a stronger bolt and you still have to interface with existing barrel extension designs and bolt carriers. Make a better extractor by making it wider and now it doesn't work with the existing fleet of bolts and barrels that are in service.

BSW

*External debris like dust, sand, and mud. I completely agree that carbon fouling in the AR is a total non-issue

 

[Shannow]

4 is an interesting argument...

take a round in a magazine, and consider its mass CofG, and how you expect that round to chamber.

Give the bolt a decent overtravel, and it carries inertia on its way back...

edit...should really go back to the SMLE !!!

 

[hatt]

1&2. Bolts aren't that fragile. If you're worried about bolt weakness treat it as a wear item and replace every 5K. Also, mid and rifle length gas systems are easier on bolts.

3. If you're concerned about extraction and already have proper insert and spring, you can add an o-ring. Link

4. I've never once heard this argument. Short stroking is an indication of other problems.

5. Get something else if the fundamental design is not to your liking. This is a military only issue. And they train to use and maintain their weapon systems. For law enforcement and civilian uses in CONUS, a total none issue.

 

[AMC]

Coming from an LE armorer with over 5 years experience, problems 1&2 are problems in theory only. Problems 1&2 are mitigated/eliminated by using quality steel and the shot peening / particle testing process. Sure a larger bolt with larger lugs would be great and all but now you are making the rest of the gun bigger with it. As suggested, by as high quality of a bolt group as you can and replace it frequently. Many experts agree having a complete spare bolt is a good idea, especially for frequent rapid fire or full auto.

Problem 3 is some what true but can be solved by extra power extractor springs and spring O-rings. Also, you are leaving one major design feature out of the extractor. The extractor is pinned slightly past the center point of its length! This causes the heavier, lugged end of the extractor to press inwards (gripping the rim better) due to inertia, during the bolts rearward travel. The tension the extractor spring provides is mostly to allow the extractor to snap over the rim during feeding and to hold the case until inertia can take over during the bolts rearward movement. Several firearms use this design, including pistols, rifles, shotguns and rimfires.

Problem 4 is mitigated by your buffer. Take your buffer out of your AR and shake it. Notice something inside there moving around? Those are a bunch of weights and rubber spacers that slam rearward when the buffer suddenly stops against the back of the buffer tube. The weights being slammed rearward cause a momentary pause of the buffer and consequently, the bolt. This gives a potentially weak magazine spring just enough time to pop the next round in the magazine up for feeding instead of missing the next round in the magazine and causing a short stroke mis-feed. The weights slamming rearward also mitigate bolt bounce during the bolt carrier's furthest rear and forward movement.

Number 5 is your most accurate complaint. The tightly fitted parts is a double edged sword. On one hand the tightly fiited parts can bind easily in the presents of particulate but on the other hand, they don't allow anything but the smaller particulate to enter. The tight tolerances also tend to heat up and cool down more uniformly, compared to larger more separated parts. With the ejection port cover closed, the AR design is essentially a sealed operating system and there isn't alot of spaces for particulate to enter. The only real space sand and other junk can enter is around the magazine and magazine well. Again, many modern designs use this theory, the most notable being the FN F2000. It actually uses a rubber gasket inside the magazine well to seal out contaminates and literally acts as a squeegee for the magazine when it is being pushed in or pulled out. The newest and IMO, the best solution for # 5 are the Nickel Boron bolt carrier groups. Nothing really sticks to the surface and the small, tightly fitted parts are essentially lubricated for life now. I believe that a quality Nickle Boron bolt and bolt carrier group are the best upgrade you can do for your AR besides using good magazines.

Sure the AR-15 is not perfect but it is well designed and works very well when it is made properly. Not many people, even many in the AR industry, know about the small design features the AR has built into it so very few people make this information easily available. The AR-15 would not be the rifle of choice for just about every modern police or military force in the world if it didn't work well! Despite all this, the AR still does have problems but a lot of it's short comings have been addressed over the years and quality aftermarket parts make the other issues easily fixable. Examples would be the BCM gunfighter style charging handles, PMAG magazines and Nickle boron bolt groups. Does anyone care to guess what aftermarket parts my AR has on it?

BSmith- You are a smart cookie. I can tell by the content of your posts and your writing skills. I did not make this post to argue with you but to help inform you. Keep up the good work and keep learning!

 

[bsmithwins]

Do a google image search for 'broken ar bolt'. Count the number of bolts broken at the two locking lugs by the extractor and the cam pin hole in the first 100 images. Bolts destroyed by overcharged handloads don't count.

For kicks image search 'colt ar broken bolt'too.

Then do the same search but replace AR with AK, Garand, M1 carbine, HK 93, HK G3, and FAL. The other popular rifles just don't experience anything like the failure rate of ARs.

ARs break bolts because the loads are higher than the steel can take. The two lugs next to the extractor take the majority of the load when firing, and their strength is compromised by being undercut for the extractor. The designer tried to compensate for this weakness by requiring shot peening, which increases resistance of the steel to fatigue crack initiation. But, once a pit forms that deeper than the shot peening affected zone, bolt failure is inevitable.

I'm not saying that the AR can't extract, just that the extraction is marginal. Lots of people have FTEx on their rilfes, usually with steel case ammo. The same ammo shot in other rifles doesn't lead to near as many reports of FTEx.

The AR relies on spring power alone for stripping a cartridge from the magazine because the bolt travel is so short. Other rifles that have overtravel get the bolt/bolt carrier moving forward first and use inertia and the operating spring to get the bolt closed.

I'm not saying the AR is a [censored] rifle. What I am saying is the AR is made like a airplane is made: highly stressed parts that need to be well maintained to function correctly and that don't have a lot of margin for non-optimal conditions.

Just wondering about the cop AR15s. How many rounds do those rifles get per year? What's the round count on your oldest rifle?

BSW

 

[AMC]

I have seen 1 broken bolt in my time in the Army, never in the civilian sector. That means roughly once in 10 years. It isn't a big surprise to me that I saw it while I was in the military either. The rifles all had very high round counts and had a 3 shot burst feature that the civilian weapons don't. Military ammo is also higher pressure than most civi ammo too. Google glock kaboom or whatever else you like, you will see plenty of pictures but that doesn't mean it happens frequently enough to worry about or let alone call it a "marginal" design. Marginal to me would mean that it barely works and almost always fails.

Other rifles have their own problems and failures just like the AR does. No one would use the AR-15 if it broke lugs frequently enough to be a major problem. None of the rifles you listed are as light weight or accurate as the AR either.

As for the steel cased ammo, The reason ARs sometimes don't extract it is the fact that it does not seal the chamber as well as brass ammo. Steel just isn't as flexible as brass and the case mouth doesn't seal as tightly. This lets firing residues and [censored] get into the chamber and wedge against the fired case and chamber wall. To make matters worse, the AR-15 has a pretty tight chamber and the 5.56 case does not have a lot of taper to it like the 7.62x39 and some others. Now, like I said above, This is where the AR is at a disadvantage. The AR's relatively small extractor and gentle STARTING grip on the case could very well lose grip on the case if your extractor spring is weak or the chamber is really gunked up. Again, marginal to me would mean the AR almost never works properly with steel cased ammo. By that same token, who expects their gun to work as well will steel cased ammo regardless if it is an AR-15 or not? Who uses steel case ammo as duty ammunition (in 5.56 particularly) where reliability is essential? Not anyone I know.

For the feeding, you are equating the fact that the bolt does not go very far back before it hits the round in the magazine and the bolt's small size to relying on spring pressure to feed. First off, I don't think I have ever seen an effective method to measure exactly how far past the rounds in the magazine the bolt goes. I have also never seen anyone ever compare bolt travel distance between semi auto rifles of the same caliber but OK. I am really not sure where you are going with that but it sounds like you are forgetting about how heavy the bolt carrier and buffer are and their combined inertia pushing on the bolt that is pushing on round in the magazine. Also consider that the 5.56/223 rem is a relatively small and lightweight cartridge, especially compared to how large and heavy all the components pushing on the cartridge are.

Then consider that the AR-15's magazine lips have a relatively loose grip on the cartridges and you can see why it usually feeds just fine. Getting back to the steel cased ammo, steel cased ammo usually isn't as slick and lubricious as brass cased ammo. This increases the friction between the rounds in the magazine and the friction on the round that is being held by the magazine lip. All the extra friction can help cause feeding issues with steel cased ammo that is normally not a problem with brass cased ammo.

The AR-15 is not my favorite rifle by any means and I am not really defending it that hard. I just think calling the ar-15's design marginal over the slight issues above is a bit harsh.

As far as duty AR-15's round counts, that depends on the department but I would say average see 1000rds per year if the department has a rifle course. If the department has no rifle course, the officer could practice with it more or less on their own. The round count could vary from 200 rds a year to 5,000 rds a year, who knows.

The round count on my personal rifle is probably around the 7K mark. The rifle is only 2 years old and has been collecting dust lately because I don't want to shoot up my own personal ammo with the way things are right now, especially the state I am in! The oldest rifle I have ever seen was probably the m-16's in basic training. Now those things were marginal! You were lucky to make it through 2 magazines on a clean rifle before they started acting up. Believe it or not, most professional users like the military and police do not keep exact round counts for their firearms. Most of them go by manufacture date and "in service date" to estimate how many rounds they have. To confuse thing even more, the AR is so modular that it is possible to have different round counts on different parts on 1 complete rifle. For example, the barrel could have 10,000 rounds, the bolt could be brand new, the lower could have 2,000 rounds, the magazine could have 5,000 rounds, or any combination. You get the idea.

To me, all firearms are a bit like airplanes! Operating tolerances, manufacturing standards, and providing good maintenance are all key to keep your airplane or firearm working properly. Airplanes have less room for error than many other mechanical devices in the world. If your AR-15 fails to extract a fired case, you perform immediate action, whatever you want to call it, Tap rack, S.P.O.R.T.S. ETC. Which only takes a second if you are practiced. Now, If something in your airplane majorly fails, you either find an emergency landing spot or religion. Neither of which are as easy or fast as immediate action for a firearm!

Regardless of what gun it is, take good care of your good quality firearm, feed it good quality ammunition and you will minimize problems.

 

[Robenstein]

The AR bolt design is only marginally strong for the 5.56 round. Probably because it was originally designed around a less powerful round and then was adapted to shoot what became the first 55gr M193 round in order to satisfy the military's revised long range accuracy and penetration requirements.

That being said, there are higher end AR parts and lower end AR parts. I am betting the lower end AR parts cause a lot of the issues with the broken bolts, especially in the shorter carbine length gas systems. And yes, compared the the Johnson rifle of 1941 which used a very similar bolt design, the Stoner AR is indeed less robust. But you must also remember Stoner and Armalite had the goal of a lightweight rifle so they made it strong enough for the time. The extensive revisions to the design since, such as shortening the gas system have created extra stress on it.

As for being overly tight, it is a double edged sword. If you look at the contemporaries that competed against Stoners design back in the day, they were built loose. For instance when the US Govt tested the FAL back in the early 50's they complained about the FAL's tilting bolt system's inherent lack of accuracy. While perfectly suited for modern warfare which studies show takes place at under 200 yards, it was not up to the U.S. military's standard of accuracy at the time. This is of course because the contemporaries of the AR were built with looser tolerances to allow better reliability and room for debris to work out of the action and not bind it up. In order to get an accurate rifle, Stoner snugged the action up.

The AR is a decent rifle. It is accurate, modular, and lightweight. But it certainly does take more care to keep it running than its contemporaries did, and of course since the early 60's newer designs and technologies have surpassed it in many aspects. But considering it was first put into the field with military advisers in Vietnam during the Kennedy administration, it has done well over 50 years. There are better rifles, but not so much better to justify the frugal military to consider retiring it just yet.

 

[bsmithwins]

My whole problem with the AR bolt is that it's overstressed. I understand the reason for shot peening the bolt; to introduce a skin of steel that's in tension, so small cracks and pits don't propagate. But once a crack or pit penetrates the compressed skin, you will get fatigue cracking as the base steel isn't tough enough given the load the two extractor side locking lugs are under.

Other rifle of similar age don't break their bolts, unless subjected to severe overloads. The M1 Garand, M1 Carbine, M1As, HK G3 (HK93), AK47,FAL, just aren't known for breaking bolts.

Overtravel has an effect on bolt velocity when the bolt's stripping lugs are trying to remove the cartridge from the magazine. That's a common place for excessively fouled and/or dry weapons to experience a stoppage.

The force available to the do the work of stripping a cartridge is equal to the mass of the bolt/bolt carrier times the square of the velocity. You can either use a stiffer spring, a heavier bolt carrier, or let the bolt carrier have a head start to get some velocity. But a small increase in velocity gives you much more force available to overcome friction while returning to battery.

I could pretty much sum up my whole argument with 'The M16 (and civilian AR) doesn't have a lot of operating margin. The design was frozen before extensive testing that would have revealed weak points was completed. By the time these weaknesses were found too many rifles had been procured, making changes too expensive.'

Did the changes to the M16 like the chromed chamber and bore increase reliability? Yes, they sure did. But any more extensive changes would break backwards compatibility with the existing fleet of rifles and aren't feasible.


Older Ordance phanmplet about small arms design factors here: https://docs.google.com/file/d/0B09fZpC9S7gDaEc0ZXhnaXJOTFk/edit?usp=sharing

BSW

 

[hatt]

"But any more extensive changes would break backwards compatibility with the existing fleet of rifles and aren't feasible."

Yep, so what's your point in these threads in multiple forums(I see THR locked that one up quick) other than to complain? If you don't like the design, buy one of the other 20 designs out there. Just about everyone else is happy to buy low cost accurate military quality DiY guns that last tens of thousands of rounds with basic maintenance with parts falling out of the sky they're so common.

 

[Robenstein]

Everything you need to know why the U.S. Army bought the M16/AR15 and why it never went smoothy can be found in one book...The Great Rifle Conspiracy. Hard to find, but shows how we essentially backed ourselves into a corner and had to buy the AR in a rush so we didn't have to send our boys to Vietnam with mothballed M1 carbines and M1 Garands to supplement the inadequate numbers of M14 rifles on hand(The production of which was already shut down by 64)

The reason why we did not pick the FAL, aside from the accuracy complaints was that it was made in Belgium...the first nation to be overrun in the previous two large wars. It was a major concern that FN would be overrun quickly by the Soviets if there was a new war in Europe. Same issue with HK there.

 

[bsmithwins]

Originally Posted By: Robenstein
Everything you need to know why the U.S. Army bought the M16/AR15 and why it never went smoothy can be found in one book...The Great Rifle Conspiracy. Hard to find, but shows how we essentially backed ourselves into a corner and had to buy the AR in a rush so we didn't have to send our boys to Vietnam with mothballed M1 carbines and M1 Garands to supplement the inadequate numbers of M14 rifles on hand(The production of which was already shut down by 64)

The reason why we did not pick the FAL, aside from the accuracy complaints was that it was made in Belgium...the first nation to be overrun in the previous two large wars. It was a major concern that FN would be overrun quickly by the Soviets if there was a new war in Europe. Same issue with HK there.





Don't know that I can agree with the FAL being made in Belgium part as being the reason why Army Ordnance didn't adopt it. The FAL was lecense built all over the world, so we know FN didn't have a problem with that. The US has always insisted that smal arms be built in the US, which is why Berretta and FN have factories in the States now.

The reason the FAL wasn't acceptable for Army Ordnance was because is wasn't designed by them. US Army Ordnance had a bad case of 'Not Invented Here' syndrome that proved fatal when they clumsily sabotaged the AR15 trials.

BSW

 

[Robenstein]

Originally Posted By: bsmithwins
Originally Posted By: Robenstein
Everything you need to know why the U.S. Army bought the M16/AR15 and why it never went smoothy can be found in one book...The Great Rifle Conspiracy. Hard to find, but shows how we essentially backed ourselves into a corner and had to buy the AR in a rush so we didn't have to send our boys to Vietnam with mothballed M1 carbines and M1 Garands to supplement the inadequate numbers of M14 rifles on hand(The production of which was already shut down by 64)

The reason why we did not pick the FAL, aside from the accuracy complaints was that it was made in Belgium...the first nation to be overrun in the previous two large wars. It was a major concern that FN would be overrun quickly by the Soviets if there was a new war in Europe. Same issue with HK there.





Don't know that I can agree with the FAL being made in Belgium part as being the reason why Army Ordnance didn't adopt it. The FAL was lecense built all over the world, so we know FN didn't have a problem with that. The US has always insisted that smal arms be built in the US, which is why Berretta and FN have factories in the States now.

The reason the FAL wasn't acceptable for Army Ordnance was because is wasn't designed by them. US Army Ordnance had a bad case of 'Not Invented Here' syndrome that proved fatal when they clumsily sabotaged the AR15 trials.

BSW


At the time it was initially tested in 1950, FN was not granting licenses for the FAL. And it was listed as a reason in Ed Ezells book. You must remember that FN would not grant West Germany a license for the G1(FAL), which is why they ended up with the G3. And yes, U.S. Army Ordnance under Col. Studler did think their designs were better, especially because they were the only ones that met their impractical standards for long range accuracy.

 

[bsmithwins]

I suspect that the Belgians were not big fans of arming the German for some strange reason.

Amusingly, I'm in Eindhoven, the Netherlands right now. Pretty much all the down town buildings post date 1945. The locals still aren't too overly fond of their neighbors to the east. Even though the Germans kicked off that big urban renewal project.

I'm sure FN would have worked out some type of license production arrangement to get the FAL accepted. Wikipedia lists the service date for the L1A1 as 1954, so the time frame is about right.

I totally agree about Col. Studler (and Army Ordance) having their collective heads firmly in the sand. Instead, they tinkered until 1959 to produce a product improved M1 Garand.

BSW

 

[Robenstein]

Indeed the L1A1 was adopted in 1954 as part of the "Great Compromise of 1953" where the USA and UK came to an agreement in a last ditch effort for NATO rifle standardization where the Brits would give up on their intermediate 270 round as a candidate for the standard NATO round in favor of the 7.62 American cartridge if the FAL would be the standard NATO rifle.

Studler and Army Ordnance reneged on the deal to keep the T44 rifle development going...and that is when NATO standardization hopes for small arms went all to heck.

 

[bsmithwins]

There was standardization. The US standardized the M14 for 5 years, then went off the rails with the M16. The Germans standardized on the G3*, and the rest of the world that wasn't getting AKs from the Sov standardized on FALs.

BSW

*I know other countries used the G3 also.

 

[Robenstein]

The original idea of NATO standardization was for all member to use the same rifle and same cartridge. So that in an event of an attack by the USSR member nations could be more easily supplied with parts and ammunition or even extra rifles. And yes, we went off the ammunition standardization rails with the M16, but we had already reneged on rifle standardization in the 50's when we did not adopt a version of the FAL and instead went with the T44/M14.

 

[bsmithwins]

At least the situation with NATO was better than WWII. Even the Brits were making 8mm Mauser ammo for their tank MGs as the .303 Brit's rimmed cartridge couldn't be adapted to work with the BESA during the war.

BSW

 

[Robenstein]

The supply nightmare of WW2 was exactly what inspired the standardization endeavor for NATO.

 

[AMC]

All the history makes my head spin, that's why I don't bother with it!

I suffice it to say that there are plenty of good guns out there. They all have their pro's & con's.

I am with the crowd that says the .223 rem / 5.56 Nato are too small for a combat rifle cartridge. They work great for a personal defense and police cartridge but are a little too small and light for serious open combat. Personally, I am really liking the 6.5 grendel but the fact that it is so proprietary and all competition from 6.8 SPC and 300 BLK are holding it back.

Here is a good read from another guy who doesn't like the AR15. Myself and pretty much anybody who is a somebody in the gun world will strongly disagree with it but he makes a few good points and you will probably get a chuckle out of it.
http://madogre.com/?p=174

 

[2004tdigls]

if 5.56 nato is too weak for you guys just convert it to 5.56 wssm, this round is going almost light speed when it leaves the barrel, it has almost 2000 ft/lb of energy compared to a 5.56 nato's 12-1300.

http://en.wikipedia.org/wiki/.223_Winchester_Super_Short_Magnum

http://www.dtechuppers.com/ar-15-wssm-upper-receivers.html