Marginal aspects of AR design.

[briansmithwins]

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 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 wider extractor 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

 

[osteodoc08]

You do realize that the M16 was developed in the 50's, correct? It was adopted and put into service in what, 1962? So for a 50+ year design, it's going pretty darn strong. There will always be advancements in design and materials. It's the natural evolution of things. Every weapon has its flaws and weaknesses (and strengths). Overall the original design is very well thought out made.

 

[Robert]

Keep this focused on the design aspect and what might be done to improve on those and this will stay open. But, as I suspect it will, if this devolves into a "ARs suck and gun x is so much better" or any of the numerous other X is better than Y threads this will be locked in a heartbeat.

 

[NeuseRvrRat]

i guess i'll just haul my ARs down to the scrap yard now

 

[taliv]

there's a cam pin hole in the extractor? i've never heard of cam pin breakages


i don't know if you're aware of this, but it's not only possible to fix that, but it's already been done by many vendors.

this is the problem with people on the internet. when vendors fix problems and improve parts and systems, they say "they're all the same and you're just paying for the brand".
the same people then turn around and say why doesn't somebody fix all these problems?

geez

btw, wider extractors don't interfere with barrels. see the much wider KAC SR15 extractor. it also uses a smaller cam pin and smaller cam pin hole in the bolt.
KAC has the sand cuts you speak about in their SR25 bolt carriers. many people say they are just for looks and sand cuts don't work though.
and their locking lugs are changed
and their extractor has 2 springs instead of one for more force.
of course, they just charge $2000 for their brand name.

JP and others use much better steel in their bolts, if you want to pay for it.

 

[briansmithwins]

there's a cam pin hole in the extractor?

Thanks. Typo caused by cutting/pasting text while I was editing.

My point wasn't that cam pins break, I was only able to find one pic of a broken cam pins on the internet. My point was that the cam pin hole in the bolt is too large, leading to broken bolts. There are pictures of lots of broken bolts on the internet, many of them failed at the cam pin hole.



BSW

 

[68wj]

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.

There is a company in TN that agrees enough with these 2 that they put some effort into the design.

1)They beefed up the base of the lugs enough to increase strength, but they don't interfere with industry standard barrel extensions. It isn't as obvious with a normal bolt to compare, but you can see the base of the lugs have a smoother transition in the valley due to more material.

A 5.56 and 6.8 bolt


2)More material left around the cam pin hole does not interfere with standard carriers. This is a common failure point in carbines from the unlocking forces applied during higher chamber pressure.

coated "superbolt"

coated normal bolt


I don't know if either of these really make a difference. It would be interesting to see some testing, but laymen observation says it is stronger and 1st hand experience hasn't suffered any negative consequences from the altered design.

Other companies such as LMT and LWRCI have variations to bolt design too. I have seen altered carriers too such as this:

 

[Art Eatman]

Over the last--aw, I dunno--thirty or more years of browsing though the gunzines, I've seen numerous articles about durability testing of ARs. Lord knows how many. Anyway, bunches of 10,000-round tests where the writer was all happified with the lack of problems.

That sorta says to me that "marginal" is in the eye of the beholder. Sure, there could be improvements to make bits and pieces better, but so far the problems seem to be rather few.

 

[ugaarguy]

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.

Beefing up the lugs by the extractor would only make the problem worse. The solution used by the Germans and by Armalite is to eliminate or reduce the size of the lug opposite the extractor, thereby equalizing the forces across the bolt, and extending bolt life.

Going to a stronger alloy on the bolt would greatly increase the chance of the barrel extension breaking. The bolt can be swapped out in seconds with no tools, and won't affect headspace. The barrel extension takes at least half an hour to swap out if you're good and have the right tools. It also controls headspace. If you have to choose between the bolt or the barrel extension breaking, you choose the bolt breaking.

None of the above really matters if you simply use a bolt that's been proofed with an HPT round, and passed MPI afterward. HPT/MPI bolts breaking before 10,000 rounds are exceedingly rare. If you can afford to put 10k rounds through the rifle, you can afford to swap the bolt out preemptively at 9k, or 5k rounds.

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.

Might is the key word. In practice cam pin breakages are extremely rare. You rarely even hear about them, much less actually see them.

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

The .mil and civvy AR shooters have learned quite a bit about the rifle after 50+ years in service. Stronger extractor springs with force increasing inserts and outserts are now standard. Further, they're really cheap. Heck, even well made extractors are cheap. Swap them out for fresh ones every few thousand rounds. Again, it doesn't require any tools, and it takes a couple minutes or less.

If you're still stuck on this, look up LMT's "lobster tail" extractor & bolt. It uses a pair of standard AR extractor springs placed side by side, and works with standard barrel extensions.

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.

Keep the rifle properly lubed. If you want to allow for over travel, you could easily shorten the buffer and use a heavier filler to maintain proper weight. That wouldn't change the modularity of the rifle at all.

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.

Debris mitigation is called lubrication. Look up "Filthy 14". ARs will run when absolutely filthy if they're kept lubricated.

Anything that relies on the operator is asking for trouble.

I guess you'd better start working a computer that identifies threats, aims the rifle, and fires it if necessary. Or maybe work on autonomous robotic soldiers. If you can't be trained to clean and lube a rifle, and keep an ejection port cover shut, then you shouldn't be trusted to use any lethal weapon. The rifle was designed for use by literate, educated, westerners; not illiterate conscripts from third world countries.

 

[briansmithwins]

We know ARs break bolts, usually above the 10k mark. I haven't seen any broken barrel extensions or analysis of stress on the extension to know how evenly it's loaded.

ARs still frequently have extraction problems. Lots of people on different forums have problems with extraction still, even with HD springs, black spring inserts, and o-ring reinforcements. Usually carbines, and usually steel case ammo, but extraction problems still exist.

I agree that ARs run better wet, and that carbon fouling isn't going to cause failures if the rifle is wet. What can cause failures is dust, sand and mud that gets into the rifle.

The rifle's operator should be focusing on other things than doing what a spring loaded door on his rifle could accomplish. I've never heard any infantryman argue that he didn't have enough to pay attention too in combat.

BSW

 

[jdh]

I've seen and been issued some very abused and neglected ARs. Only broken bolt I've ever seen was a 7.63X39. A cartridge for which the gun was never intended to be adapted.

Eliminate the cam pin hole, you say. No cam pin hole, no cam pin. No cam pin, no bolt retention.

The extractor has enough grip to rip the case rim off of a stuck case. Seems like the case is the weak point not the extractor.

Are you referring to the ArmaLite Rifle? The bolt has to travel nearly half and inch past the base of the top cartridge in the magazine to clear the bolt hold open.

The other side of that coin is the AR has less openings to allow the entry of debris than does the AK, FAL, G3, and such. Less gets in, less to need to deal with. BTW, not all FALs have sand cuts. Also I suggest you closely examine a bolt carrier from an AR for spots where the finish has worn from contact with the inside of the receiver. Other than the edges of the cam pin and the carrier rails there is not that much. Leads on to believe there is more clearance in there than is commonly assumed.

No the AR is not perfect. Since it is designed by man and given that man is an imperfect creature it cannot, therefore, be perfect. However, it is also not the poorly designed POS is is credited with being.

 

[brian923]

Adding a spring loaded door in the mix would be adding more over engineering. Another thing to malfunction.
The operators job is to use his rifle as a tool. No matter who or what the operator does for a living (military, spec ops, recreation, hunting.....) it is the operators job to keep his tools clean and upkept. If your bolt last to the 10k mark, its not that expensive to replace such a high stressed part... heck, at 10k rounds its probably not a bad idea to change out the barrel as well. (I know chrome lined barrels can last longer, but again, not that expensive nor hard to do.) I know the 10k round count is completely subjective to what the rifle is used for, but these are just my $.02.

 

[briansmithwins]

Common failure points on AR bolts.











BSW

 

[Fishbed77]

ARs still frequently have extraction problems. Lots of people on different forums have problems with extraction still, even with HD springs, black spring inserts, and o-ring reinforcements. Usually carbines, and usually steel case ammo, but extraction problems still exist.

I'm going to go out on a limb and say that, since the AR is far and away the most popular semi-automatic rifle in America, frequency of extraction issues (or any other operation-related problems) are no more common for it than any other popular semi-automatic rifle design. Heck, I've heard of extraction issues with AKs and even the mighty M1 Garand.

You do, however, have to try pretty hard to break a Garand bolt. But it can be done.

 

[ugaarguy]

We know ARs break bolts, usually above the 10k mark. I haven't seen any broken barrel extensions or analysis of stress on the extension to know how evenly it's loaded.

I doubt you'll ever see a broken barrel extension. The slightly weaker steel chosen for the bolt prevents it. AR bolts are cheap, and as already stated, they're very easy to swap out. Also, what firearm doesn't need maintenance and a minimal overhaul at 10k rounds or less.

ARs still frequently have extraction problems. Lots of people on different forums have problems with extraction still, even with HD springs, black spring inserts, and o-ring reinforcements. Usually carbines, and usually steel case ammo, but extraction problems still exist.

I saw plenty of extraction problems with ARs when I worked for a large retail FFL with a gunsmithing / repair department. Almost all, if not all, of the extraction issues were caused by undersized and or improperly finished chambers. This is why I constantly advise against purchasing an AR made Olympic, Bushmaster, or DPMS, because rifles made by those companies frequently came back with tight and / or rough chambers.

I agree that ARs run better wet, and that carbon fouling isn't going to cause failures if the rifle is wet. What can cause failures is dust, sand and mud that gets into the rifle.

Lubrication defeats sand, dust, and mud in the same way it defeats carbon fouling. IIRC there are even recently disclosed Soviet documents advising heavier lubrication for optimal performance of AK rifles in dry sandy / dusty environments.

On the other hand, the series of small improvements that eventually lead to the M4 TDP are largely what have made AR rifles as reliable as they are today. If you can find a way to make additional improvements and retain the rifle's modularity go for it. Those little things really do add up.

 

[Robert]

Ok, stuff breaks. I don't care how much you over engineer something, it can and at some point will break. So what's you point? Taliv and others have pointed out that many of the gun makers have already addressed these issues. Do you have ideas on how to fix these issues that have not been tried before? Or is this just a thinly veiled ARs suck thread?

 

[wally]

i've never heard of cam pin breakages

I had a cam pin break, rifle still functioned as I only noticed it when I removed it for cleaning. Split into two pieces at the hole for the firing pin.

If you shoot enough stuff will break, fix it and keep shooting! I really pay little concern to stuff that breaks and is only noticed after I'm done shooting. At that point its just normal maintenance.

 

[MErl]

Can we touch on ergonomics and that charging handle? A non-reciprocating side handle is much easier to use.

 

[briansmithwins]

Ok, stuff breaks. I don't care how much you over engineer something, it can and at some point will break.

No, major components aren't supposed to break.

ARs have habituated people to the idea that rifle bolts break. But other rifles don't break their bolts. Barring overloads or other extreme abuse AKs, Garands, M1 Carbines, and M1As all typically run their bolts until the receiver is worn out.

Never been around FALs or G3s enough, but do those break bolts?

When the '03 Springfield suffered broken bolts, that was a problem. Not just 'EH, stuff breaks.'

BSW

 

[Robert101]

BrianS,
I sort of get the point of your initial posting, as you want to improve on the AR design components. I have a different opinion as to what degree you question its weaknesses. Searching the internet for one broken pin and stating that the bolt is prone to breakage just don't view as legidimate proof. There are a number of substandard bolt manufacturers out there which have given the design a bad rap. Most average quality AR rifles will do +15,000 rounds of heavy use. That tells me something about the fundamental design.

 

[goon]

Aren't a lot of the issues with AR's attributed to the higher stress put on moving parts by a carbine-length gas system?
If that's the case, use a mid-length or rifle-length gas system and you should cut a lot of failures out just from that.

I ask this as an honest question - I like a lot about the AR's and have a couple on the wishlist, but I'm no expert (and I can't even pretend to be on the internet).

 

[Robert]

Ok, so what needs to be done to fix these issues?

 

[briansmithwins]

Ok, so what needs to be done to fix these issues?

I don't know that they are fixable within the constrains of the AR system.

Bolt- Beefing up the bolt would break appreciably would break parts commonality.

Camming- There is only so much room for the cam pin and the cam pin track can't be lengthened much to slow opening (like the AUG or SCAR) because you'd interfere with the gas key.

Extraction- Ideally you'd want a wider extractor but having 7 equally spaced lugs limits how wide you can go.

Overtravel- If you used a shorter buffer the gas key would start impacting the buffer tube lip. You can't change the length of the bolt carrier and use the same receiver, either.

Debris mitigation- Even if you add sand cuts the garbage has to go somewhere. The AR's tight fitting trigger mechanism already has minimal clearance for external debris. Shoving more dirt into it is only going to cause problems.

BSW

 

[Welding Rod]

I think the premise that the listed items are problems is false.

Everything in a design is a compromise. In the case of the AR many compromises were made to make the gun light, accurate, controllable, and reasonable in manufacturing costs..

Every mechanical device has a service life. If the expected service life of every component in an AR was 30K rounds, some would exceed this and complain the service life wasn't higher yet.

The buyer / user needs to understand the realities of service life, have realistic expectations, and replace components, or even the whole gun periodically.

Some component failure is due to low quality parts put out by cut rate manufacturers, some failure is due to occasional QC errors by reputable manufacturers, and some are due to use beyond component service life. These are the same reasons you might experience a soft bolt, or a broken firing pin or hammer in a M1 or M14 clone.

When the number of ARs in service today is balanced against the frequency of parts failure of components from reputable manufacturers that we see reported, I just dont see validity in this topic's premise. If a shooter or agency selects the particular compromises that make the AR what the AR is, and which make it so good at what it is good at, it seems odd to me to then expect it to be something else.

 

[goon]

I don't know that they are fixable within the constrains of the AR system.

So call it an AR-15 2.0.
What would you change? Could a bolt with fewer lugs be designed with alterations made to the barrel extension to make it fit? You'd lose some parts commonality, but if it could still fit existing barrels and receivers, not that big of a deal.

While we're at it, why not just redesign the whole BCG? You could include your sand cuts in the carrier, redesign how the cam pin works and maybe its placement and size, and redesign the bolt and barrel extension. You could presumably do a lot as long as you could make it not require a proprietary upper or lower.