AMEN

I have yet to buy any Pmags
But there 20rounders do look like a winner

Well you wouldn't believe it but you're more likely to have problems with their 20's than the 30 by a large margin.

Yes dwell time,  port location further helps on powder burn, ammo deficiencies, but there is also in inherent time delay.  The carbine was not the original design.  The location ended up being decided from an ass backward approach to keep the bayonet. What product, that is complicated doesn't suck until it is .made in large production and undergoes improvement.  Just saying the gas system was better. Middy is also better than carbine. .

I can say for a fact that I believe that is totally possible.
I've shot cleaning rods through things I thought could stop them, amazingly they flew pretty straight.
I had some pictures of them bent into a candy cane after being shot at concrete walls from 50 yards away, and they spark when they get there.

I think you have a misconception, namely that AR-15s started out marginally reliable, and are now very reliable.

The reality is that AR-15s started out very reliable, went through a troubled patch, then became very reliable again.  The stuff you hear about design changes were really not that critical, and anything you hear about selection of propellent powders is pretty much bullshit.

For discussion of what went wrong with the AR-15 in 1966-67, I recommend this thread

I have to respectfully disagree. The carbine length gas system was developed for the 10.5" & 11.5" barrels of the XM177 series.
I would say the 14.5" barrel with carbine length gas system has excessive dwell and the 16" barrel with carbine length gas system is even worse.

After implementing stronger extractor springs, stiffer extractor spring buffers feed ramps and improved magazine springs and followers to make them run right they are still known to break bolts with enough regularity that carrying a spare bolt has become common practice with large numbers of owners of AR's with those systems.

The threads and archives are brimming with threads on the subject of HP/MPI/broken/spare/replacement bolts and debates about replacement interval.

If you think rifles don't kill bolts also, you're dreaming. Every wonder if maybe we see more broken carbine bolts is because they're more popular  because most people use a carbine in courses? Further, there are plenty of untested (mpi and hpt) bolts out there. Manufacturing defects are hardly the fault of the gas system.

Its always a good idea to have replacement parts for any machine, especially one you may bet your life on. A prudent owner hardly means the system is unreliable or "destroys bolts".

Before you ask why we don't see midlength bolt breakages... the system was only recently made popular. There are still less midlengths (by a wide margin) out there right now.

Also, a 14.5 carbine has almost the same dwell time as a 20" rifle. So, I'm not sure what you're trying to say about that. It operates at a higher pressure, yes, but that's different from dwell time.

If you don't like carbines, feel free to send them to me. :)

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Our department uses a lot of DRMO M16A1's and they are very reliable.

Not dreaming just remembering. Perhaps some one who started fooling with these things in the late 60's or maybe the late 50's would have a better perspective than those of us who started in the late 70's

I do not have the number of M16 and M4 bolt failures since day one for each system, AMCCOM will.  
I think it is safe assume for the sake of discussion that the bolt failure rate is significantly higher in M4's than M16's as the ARMY never felt rifle bolts needed improvement or it would have been addressed long ago.

The M4 is a different story according to the SOPMOD Power Point.



That is precisely the reason we see them. The cause for the failure has already been discussed.

Before Carbine courses, before urban rifle, before tactical rifle, before practical rifle,,, all the way back to the late 70's when we called it Combat Shooting, we did it with rifles ( some still do) and outside of a bore obstruction, bolt breakage was unheard of with rifles.



HPT/MPI only means the bolt had not failed and had no surface flaws detected at the time of testing and nothing more. Plenty of non tested bolts out there still running strong.

All of the bolts that have failed in the ARMY's M4's were HP/MPI tested.
The same HPT/MPI bolts as well as non HPT/MPI have been serving in rifle applications long before the invention of pistol grips and inserts designed specifically for stowing spare bolts.

Search the archives.



Never said they were.  
Carbine length gas systems impose undue stresses on the bolt and locking lugs when used on barrels of greater length than they were designed for.
This has been covered and the math done on this many times over.
HPT/MPI bolts from reputable manufacturers do fail in carbine length gas system carbines so either the manufacturers QC/QA is flawed or the application of the design is flawed.



Indeed the prudent owner becomes aware of the weaknesses inherent in the mechanisms they employ and plans and adjusts accordingly.

Since this place was list server there was no consensus that I remember implying the necessity of keeping a spare bolt for rifles.
A good idea, sure but not an implied requirement like the majority of posts on the subject as it pertains to carbine length gas systems carbines alludes to.

BTW, "destroys bolts". sounds like something from a anti D.I. or AR15 type hater thread.



In the  the mid 90's the rifle was en vogue and the carbine was beginning its ascendancy in popularity. Things have changed and will continue to do so. Mid Length has been with us since the mid 90's along with a good reputation since then.



The Carbine length gas system was designed for the 10.5" & 11.5" XM177 series.

Dwell time and residual chamber pressure are correct for that application.

Hanging 3" to 4" more barrel in front of the gas port than the system was originally engineered for does raise the numbers above the original figures for that system and it shows in the math and in the results.



Certainly,,,,but I'm down to just one left and I would need a mid or rifle length gas sytem to replace it with



E.T.A.  on the locking lugs

I found this interesting, can you back up this claim?

Bayonet was the lesser part of the equation.
Compatibility with rifle grenades and rifle launched flares was the greater part.

Sorry I don't have my notes available on this one but search the web and our own Retro Forum on the subject.

http://www.inert-ord.net/usa03a/usarg/rg/

TM-43-0001-29

chrome lining, better maint,correct powder,and a better buffer!

Double tap.

The myths of unreliability were overblown and 50 years of battle-tested testing & evaluation tends to iron out out alot a kinks.

The outlying problems have been resolved long ago. I think the stigma just stuck. It has gone through a lot of configurations through the past few decades.

On the cleaning rod thing, I've fired a couple with blanks. One into a bus at about fifty yards. It put a huge dent in it and drove about an inch in. Unimpressed, I fired another into a dirt berm from a few feet away. That one was never recovered. It went in deep enough it was taking too long to dig out.

I've had a few years with M16A2's and loved them. The only issues I ever encountered were shooting mags that had been low-crawled through mud on one occasion, and they can only take so many of those nasty blanks (I'd shoot everyone's blanks that didn't want to spend time cleaning their rifle). I did have one shitty rifle. It went bang every time, but was otherwise really wore out. It shot poorly, had a terrible looking bore, the trigger pin would try to walk out the receiver, and the upper and lower were so loose fitting it was almost comical how badly the upper flopped around. It looked like it had had a rough life.

I have a AK; a Romanian PSL...and it looks shoddy compared to any AR. It has one magazine that jams every now and then, and has had a few random light strikes. It will rust in humid environments pretty quickly, as well. It otherwise works very well. My AR on the other hand, has never given me any issue.

British SF (Pathfinders) do use the SA80 these days, as well as the Diemaco. I have no idea about the others, but since the SA80 now has better optics, and for several years has had accessory rails fitted, they may be using them. Apparently even the weight is being addressed, although it'll probably just shave off 2lbs (if that). The A1 was fairly poor, and for years all it typically had provisions for, apart from bayonet, UGL, etc, (including on the A2) was the SUSAT, which had a special mount design not suited to standard optics.

Off-topic (sorry OP), but hopefully of interest to someone, what with the lack of information about them abroad.

The carbine length gas systerm was originlly developed basically by cutting a standard barrel in half.  The original length was not 10.5" but 10".  

I'm not going to go completely into the history of the carbine length gas system again in this thread, but suffice to say - when the gas system length and barrel length combination proved to be unsatisfactory, Colt tried several different things to improve the gas system function - including an intermediate length design.  On after about ten years of testing and development, including deployment to Vietnam does the 14.5" barrel appear - not related to bayonet usage.  The 14.5" barrel length is the result of progressively adding dwell time to the carbine length gas system to find optimum reliability.  

The 14.5" barreled carbine has an unparalleled pedigree of faithful service and combat reliability and I've yet to be convinced that intermediate length gas systems alone are a particularly significant improvement.  Realize as well the amount of use and testing that the 14.5" carbine has seen in FA use.  FA exposes many many many reliability issues that are practically unknown in semi-automatic function.  It exposes all sorts of problems with timing, bolt bounce, gas pressure curves, ect. that you will never ever see, even in high volume SA firing.  While midlengths do well in semi-auto, many semi-auto rifles inexplicably (seemingly) hiccup in FA.  FA fire is what killed the R605, the XM177, and exposes the flaws in "lower rent" complete rifle systems in use.  

The 14.5" carbine, on the other hand, properly sprung and balanced and timed has been tested and used in combat and training in FA reliably for decades, and been continually improved over the years using operational feedback in operational conditions ranging from Arctic to equatorial - in the driest deserts to the most humid jungles and is still the leading choice of troops from all nations where there is operator level input on weapon selection.  Midlength gas systems have a long long long way to go before they have the reputation for utility and reliability that the 14.5" carbine has.

Even now, I can only think of two military weapons (not regulated by NFA and where operators have a strong say in primary long arm selection) that use something other than a 14.5" carbine length gas system:

The Diemaco (Colt Canada) SFW which was specifically requested as a 16" carbine, not to mention that it's a weird platform to begin with, and the mythical "recce" which examples of which in *actual* use that use a different operating system is probably closer to a dozen than 100.  

Re: the "theoretical" advantages of the midlength gas system, reaching back to the beginning of this discussion, as originally advertised, "theoretically" the AR15 didn't need to be cleaned at all anyways.  We see how that worked out.  

~Augee

This may be a little off topic (not related to DI gas system).  I have heard that the m16/m4 platform have a history of barrel and receiver extension breakages during bayoneting and butt strikes.  Even that the Army had started using plastic bayonets to prevent breakages of the barrel during training (I guess the plastic bayonet breaks before the barrel).

No.

You're probably thinking of "Rubber Duck" M16 rifles

the bayonets were real,  the rifles, were not...

http://en.wikipedia.org/wiki/Rubber_duck_%28military%29

http://www.armynavysales.com/products/vietnam-m16-trainer-rubber-duckie/

I would say magazines. We're lucky to have access to well made reasonably priced magazines now.