M16/M4 reliability problem, increased bolt friction causing jams

DESCRIPTION / updated May 2010:
AR15 modification chart:
http://troubleshooterberlin.fileave.com/AR15%20modification%20chart%20May%202...

Regarding the functional reliability of the AR15/M16 system there is one problem I have never seen mentioned anywhere - increased bolt friction.

On its forward move while feeding the next cartridge the bolt has to overcome the friction between the specific mag lip and the cartridge below (depending on how much the mag spring is compressed).
The bolt carrier is pushed forward by the bolt spring and the bolt head hits the next cartridge in the magazine. The bolt head is now trying to move rearwards (resistance/drag of the cartridge in the mag) and to make its turning move but it can't.
The head of the cam pin is pressing against the left inside of the upper receiver (until cartridge is released by the magazine).
Thus pressing the bolt carrier in the opposite direction causing the bolt carrier to twist clockwise creating additional pressure on all bearing surfaces. With just a small amount of dust/dirt there it slows down the bolt which may not have enough speed and power anymore to close completely. Because at the last few millimeters the bolt has to overcome the power of both the extractor and ejector spring.

And it seems as if the designers in the mid-sixties were aware of this problem.
Therefore the forward assist is located at the right side. So the forward assist not only generates forward pressure but also a counter-clockwise strike at the bolt carrier to rattle it free.

Actually most of the other contemporary designs using AR18-style bolts (G36/XM8, FN SCAR ...) show the same built-in flaw. But don't suffer so much from this early turn matter due to the different shape of the bolt carrier, different location of the contact area cam pin/receiver (9 vs. 12 o'clock) and clockwise locking turn.

UPDATED - HK416

Why proved the HK416 to be more reliable?

Larry Vickers:
"HK 416s utilize a 20-percent stronger buffer spring, which produces more bolt velocity."
The stronger buffer spring (more momentum on the forward move) is needed to compensate the higher impulse generated by the gas piston system.
Additionally the HK416 uses a "spring-powered" bolt head.
Means the bolt head is pushed forward in the bolt carrier.
This works against the drag force of the magazine and forces the bolt head out of the "jammed" position.
The AR15/M16 bolt head stays in the slightly rearward "jammed" position (on the forward move of the bolt) due to the friction caused by the gas rings.
This spring serves as a rebound spring for the firing pin as well to interact with an internal firing pin safety (apparently this became neccessary due to the higher closing energy of the bolt carrier).
But this is not the only reason for it's implementation otherwise that spring would rest against the bolt carrier and not against the bolt head.
http://img40.imageshack.us/img40/9709/hk416firingpinsafetyab.jpg

AK
The AK bolt head (like some other designs) is not forced to rotate earlier than needed to lock.
http://img171.imageshack.us/img171/8461/img3216yup2.jpg
The bolt head is pushed forward by the "stop edge" (yellow) of the bolt carrier.
The bolt head is forced to rotate if it's reaching the little ramp (encircled yellow). This rotates the bolt head enough that it's guide cam will pass the stop edge and will be now forced by the bolt carrier to continue it's rotation.
If an earlier try to rotate (like at the AR15/M16) is not an issue - why did they design it that way?

Try it (no risk to pinch your finger):
http://img530.imageshack.us/img530/2728/3395trb3abc2.jpg
The upper won't move or sag a bit and stop then.

April 2009:
There are recently a few discussions going on about „The Groove"—Theory or "the cam pin groove thing". It's about wear marks in the upper receiver caused by the cam pin.
http://img257.imageshack.us/img257/1715/wearmarksupper.jpg
And there you can find the following answer:

Sent: Friday, March 27, 2009 9:21AM

Jason,
The groove you are seeing is completely normal. And is common among even DI rifles. It is a result of the cam pin acting on that surface during the feeding operation. It is not dangerous and it will stop eventually.
Joe Devens
LWRC International

And here are some very nice pics by LWRC that show the interaction cam pin / guide channel in the upper receiver:
http://img512.imageshack.us/img512/336/lwrc3d5.jpg
http://img512.imageshack.us/img512/8677/lwrc3d2.jpg
http://img512.imageshack.us/img512/4890/lwrc3d1.jpg

May 2009:
POF-USA Roller Cam
http://www.pof-usa.com/slideshow/rollercampin.html

January 2010:
LWRC Advanced Cam Pin
http://www.lwrci.com/p-89-advanced-cam-pin.aspx

March 2010:
The Big M4 Myth
http://www.defensereview.com/the-big-m4-myth-fouling-caused-by-the-direct-imp...
Check out: Here are the findings of my testing:

Category:

Science & Technology

Tags:

• M16
• M4
• AR15
• sand
• dust
• jam
• bolt
• friction
• groove
• cam
• pin
• stoppage
• drag

[agsd619]

You are right my friend it is a minor flaw in the AR15 design and everybody here thats posting stupid comments obviously haven't been to combat so they don't know how it affects the weapon during prolong firing and rugged terrains with alot of debris. The solution is simple buy a POF roller cam pin. It's round and there's no friction what so ever and it will never get stuck !

[troubleshooterBerlin]

@agsd619

Thanks! The roller cam pin - I referred to it in the description to this video - came out May 2009 IIRC, about 8 months after this video was published and got some nasty bashing...

[chopperwheels]

Styre or how ever it is spelt the Aussies use them

you can out it in sand under water and then out in action still works

takes a pounding in all conditions but still lets a round out when u need it

then you clean it at night or as safe to do so and all is ready to go again!! have used it after it is pulled from the water all good reilable as ever

as with all things aussie army we have to use what is good because we don't have many men!!!!!!!

[troubleshooterBerlin]

@chopperwheels

We spell Steyr like “fire” and the S like in “shrapnel” so like: shtire

BTW – just working on an upgrade stock for the AUG making it really ambidextrous and better ergonomics.

[TheThedot]

If you increase the gas flow, for more power??? would that not take care of the weak spring issue???

[troubleshooterBerlin]

@TheThedot

You might need more gas pressure when using heavier buffer and/or buffer springs. Both would give you more momentum for the bcg on the forward move. But I would simply try. As long as you don't experience short-stroking with your bcg the gas setting is ok.

[14goldmedals]

@hedonistic1979 if you read any of my posts on youtube regarding airsoft they're pretty much the same. "Airsoft fags should stop wasting youtube's bandwidth, non-gun owners don't get it and don't care. Gun owners wish you'd fall on your rubber bayonets lol. You give real gun owners a bad name." And kids that post video game dog fights or combat missions need a serious bitch slap too.

[PeytonManningguy]

Time to get a new rifle....

[hedonistic1979]

@14goldmedals CST? I am proud to be a usetobe preferred to has-been and far better than a wannabe. I am a security guard for the Army we have a wannabe has never been trainer. A man who knows it and is not afraid to make it up. That is the type I despise loathe and detest. To give you an idea this arisoft warrior was nearly kicked out of an Army SRT course for not only trying to teach the class but tiring to tell decelerated combat veterans he knows better.

[14goldmedals]

@hedonistic1979 thank you Sir for your previous service to your country and well earned "usetobe" status. I hope you don't mind me using that moniker, it's catchy! I'm what you would call a usetobe Cst. lol

[hedonistic1979]

@14goldmedals I am a usetobe I have been out of the military for four years now I have a glock with a rail because without was not an option, I have no plans to hang anything on the rail. Hand held lights are the way to go for those of not on SWAT or in Special Forces.

[14goldmedals]

@suckyalaterhead now you know what the serations on the bolt's sides are for. In the field the prepared grunt grates a little fresh parmesan cheese over his spaghetti MRE then cleans the weapon before sitting down to chow. Not really, but really.

[14goldmedals]

I've owned a Swiss PE90 based civilian semi-auto. Believe it or not it's non-restricted in Canada but was banned for years in the USA as a Sig550 assault rifle. Crazy. It used a piston system that is similar to what some companies have added to the AR platform, HK416 for example. I like the evolution of the AR but with the short stroke piston I'd trust my life to it. Without the piston Swissarms Classic Green.

[14goldmedals]

@hedonistic1979 given your examples I would agree with "your" need for a rail. For me it's just one less edge to snag coming out of the holster. In my life if I end up in a shoot/no shoot situation it's gonna be up close and no light required. And you do have the tacti-cool sales pitch figured out perfectly. Tactical, Sniper, Entry, 3 words that sell anything to wannabes.

[hedonistic1979]

@14goldmedals That was sarcasm, your Sig was engineered by the Swedes or the Swiss I forget witch. At the time they partnered with the Germans to build it because of their export laws. Yea the American built Sigs are not as good that is why mine is also German. The rail is not useless when I was a dog handler it was great when I needed a gun a light and had a dog on leash. Unless you have a dog a shield or are on an entry team rails are just tacti-cool.

[14goldmedals]

@hedonistic1979 the Germans are some of the best engineers throughout history. German firearms are expensive for a reason, they are the best. Models that get assembled outside of Germany are not quite as good IMO. That's why my SIG P226 says "Made in W. Germany" on it and features no useless rail or picatinny mount.