AR-15 Cycling & Operation Discussion
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Old 11-29-2010, 04:58 PM   #1
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Default AR-15 Cycling & Operation Discussion

One other consideration; from lessons learned in combat, it has been found that the M4, with it's 16 inch barrel has more cycling problems than the longer 20 inch barrel of the M16. This is due to the shorter gas tube having less room to dissipate some of the gas pressure, which in turn causes a quicker cyclic action. This translates into a cyclic speed of 900+ rounds per minute verses 750 rounds per minute. This results in the bolt arriving at the next round before it it completely seated correctly in the magazine. Best case scenario at this point is that you have a stoppage, and you have to eject the round manually and manually cycle the next one. Worst case scenario is catastrophic failure of an accidental discharge, and your weapon blows up in your face.
You have three options to resolve this issue, depending on how much you fire your rifle.
1. Cheapest is to put an 0-ring under your extractor, which will force it to strip the next round out of the magazine. If you fire a lot of rounds, this is not a viable answer as you will end up with a broken extractor before long, which ends up as a projectile coming out of your ejection port
2. More expensive (and safer) solution is to swap out your milspec buffer with a hydraulic buffer, which will last about as long as your barrel, and if it fails, will not cause any damage to other parts of your rifle. If you fire your rifle once a month or more, this is a reasonably priced option, running about 70-80 bucks.
3. Most expensive, but longest lasting solution, is to convert to a piston system, which can run $300 and up, depending on which brand you get. If you can change a gas tube, you should be comfortable with installing one of these systems. They not only slow down the cyclic action, but they are significantly less time consuming to clean. They also keep the heat out of the bolt carrier group, which reduces the opportunity for accidental discharges due to a cookoff if you are firing a lot of rounds.
Hopefully some of this information can help out. May you have many successful days at the range.

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Old 11-30-2010, 01:26 AM   #2
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Welcome to FTF, fsted! I read that you have served in combat? Since that was a little vague, I'll assume you meant in the US military. If so, thank you for your service! Have you had a chance to go over to the Introductions forum and tell us about yourself?

After much troubleshooting, I really believe that it came down to the crappy Remington UMC ammo. I have 50 left and I will probably never fire them unless my life is at stake and I am out of ALL OTHER ammo. And even then I may throw my empty 1911 before using that crap again.

All other ammo, all my magazines, cycled without a hiccup. THAT ammo, in any magazine, had problems.

The hydraulic buffer sounds really cool. I will look into that. As far as changing the action, I would just save that for another build.

Thank you for your input!

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Old 11-30-2010, 11:17 AM   #3
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I have served, but not in combat. I have Soldiers working for me that have. One was in a very bad firefight when he was attached to an SF unit, and I draw on lessons he and others have passed to me. Been to the firing ranges many, many times. I own 4 AR's, all of which I have built and fired thousands of rounds through. I have run into just about every problem that an AR can generate, most usually related to the gas system. A few years back I bought a piston system from Ares and installed it, and so far it has worked smoothly. Bushmaster bought their piston system, and now when someone wants me to build them an AR, I put a piston system in instead of the gas tube. Costs more, but much more reliable, and less time cleaning afterwards. I am now in the process of building my first 80% lower, which I am taking a lot more time than what was advertised as the average time to complete, but I want to make sure I get this right the first time.

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Old 12-02-2010, 01:48 AM   #4
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As has been said many times the midlength direct gas impingment system is an ideal solution to inherent cycling problems of the carbine length DI system in a 16" barrel (carbine length actually works quite well with 14.5). Matching up the ideal gas system length with the barrel length is much cheaper and even more reliable than going with a piston system in a new build.

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Old 12-02-2010, 12:52 PM   #5
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Quentin,
The individual owner/shooter has to make his own evaluation, depending on how much he is shooting the gun, and what his expectations are. When I installed the piston on my gun, I was going through about 1000 rounds a weekend, sometimes going through a couple of hundred rounds between cleanings, which was more than I ever did for uncle sam. I needed to find a solution which was more reliable so I didn't have to worry about stoppages due to carbon buildup, which is why I switched to the piston. It isn't for everyone, as for many it simply wouldn't be cost-effective. I went through 3 barrels on my Ares piston, and it never malfunctioned, which meant when I was competing, I could focus on the shot, and not worry whether it was going to fail.
My intent was to introduce the alternatives to the author of this thread should he not find a resolution to his dilemma. I know the pros and cons of the impingemnt system. I have taken the Colt Armoror's course, and published a research paper on the subject at the Army NCO academy at Ft McCoy Wisconsin.
The US Army is upgrading the M4 to a piston system next year, the cycling problems being one of the issues driving the move, since the weapons are going to also be switched to full auto instead of the three round burst. Also, the piston is less prone to stoppages due to sand and soil. Some of these conditions the recreational shooter will never encounter, so he has to justify to himself the added expense of upgrading his firearm.
If switching to a different manufacturer of ammo resolves the cycling problem, then there is no need to seek any modifications. If not, a hydraulic buffer may be a consideration. Also, a roller cam pin on the bolt carrier group- POF-USA Patriot Ordnance Factory, Inc. -instead of the milspec cam pin may be a way to go as well. My gun keeps shooting at the range while many others are taking their unmodified carbines and rifles apart for cleaning or repairs.

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Old 12-02-2010, 09:34 PM   #6
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fsted2a, it's good to see improvements to the AR-15/M16 family of rifles over the years but as far as reliability a piston system is not superior. Listen to Larry Vickers and Pat Rogers and other highly experienced firearms instructors who see tens of thousands of rounds a week in their carbine classes and you'll hear again and again that direct impingment is highly reliable as long as you buy a quality rifle, magazines and ammo in the first place then don't dick around with it other than normal maintenance and lubrication. It's routine to reliabily go through many hundreds of rounds without cleaning a DI rifle. Just a shot of lube once in a while.

I'm not trying to talk anyone out of a piston, if you want one that's fine. But no one should fool themself that they're buying a higher level of reliability. Sure it's easier to clean and is more likely to pass a white glove inspection and if that's what you want then great. Also I'll be flabbergasted if in the next decade the US Armed Forces dump the DI M16/M4 across the board. No way, nada, never hachi GI...

Guess we're drifting off topic and I think Chris has worked out most of the earlier problems.
ETA: This last line above only had meaning in an earlier thread that these posts were pruned from.

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Old 12-03-2010, 01:15 PM   #7
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Quentin,
We can go back and forth forever with the DI-v-piston issue, but it is a done deal with the Army; don't know about the rest of the branches. There are a few reasons, some of which you may or may not agree with. One is that the shorter gas tube on the M4 carbine, which is what the Army is going to replace the M16 with, has a faster cycling action, 900 rounds per minute verses 750 for the longer barrel M16, which causes more cycling problems, especially on full auto. Another reason is mostly relevant to SF operations. On amphibious missions where Soldiers may have to fire immediately when leaving the water, when water gets in the gas tube, it multiplies the pressure, thereby creating a catastrophic failure (weapon literally blows up in the shooters face) about 90% of the time. Piston systems have not done that under the same scenario.
Most recreational shooters don't shoot more than a few hundred rounds in a weekend, much less a day. When I decided to put my piston system in, I was just getting into bumpfiring as a sport, and the ammo was a lot cheaper than it is now. It was nothing to go through a thousand rounds in a day. Ammo has gotten way to expensive to do that now.
I lost some accuracy and range when I converted my carbine to a piston, but that was not my major concern at the time. I was having a lot of fun without the expense of buying a registered machine gun. And yes, I have seen some DI rifles shoot a lot of rounds without much trouble. Just not THAT many. When I got my first AR, I didn't know as much about the system as I do now.
Eugene Stoner designed a masterpiece which had an accurace and range extremely close to that of a bolt action sniper rifle. Soldiers and Marines are taking head shots at the outer maximum effective range of the weapon, so don't think I hate the system altogether. Unfortunately, it is being tasked to do actions which it was not designed for, sometimes temporarily filling the role of a light machine gun, and that is the driving force behind the decision to make the changes.

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Old 12-03-2010, 05:27 PM   #8
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All,
I know this was suppose to be a discussion about a build, and someone took a small part of my post to heart and it ended up getting moved out of the "First AR-15 Build...here I go" thread and created a thread of its own. The piston I installed suited MY needs, but it may not be a practical solution to most of you. I like to tinker, and I enjoy working on my AR as much as shooting it. Only one of my 4 AR's is a piston, the other three are DI 20" long guns. If I want to have a long shot or tight group, I use the DI. If I get lucky and get some ammo, I use the piston.
My piston system works real good, but I know like everything else, there is a lot of crap out there. Eugene Stoner and Mikail Kalishnikov are both probably laughing their a** off at all of us now.

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Old 12-03-2010, 05:50 PM   #9
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Informative stuff in this thread, I like it. I will pay close attention to this one as I am going to be building either a 16" or 20" bull barreled AR here in the very near future. The rifle will be used for target shooting and varminting by the little woman, so it is going to be a DI gun for sure. Rate of fire will be very slow, most of the guns life it will be single fed. My question is, why would you lose accuracy or range simply because of installing a piston system?

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Old 12-03-2010, 06:20 PM   #10
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Squirrel_Slayer,
A 20" DI gun is the most accurate long gun assault rifle on the planet-PERIOD! The reason is the gas goes directly to the bolt carrier assembly, thereby making the most efficient use of the least amount of gas pressure. I am the first to admit that skinny little tube was a stroke of genius by Eugene Stoner. The connecting rod/piston assembly takes more gas to push the bolt carrier group back, how much so depends on the design of the particular system, some more than others. The two that take the least are the Ares/Bushmaster and the Osprey design. Mine is the former. I notice about a 5% variance with my Ares setup, which isn't enough to bother me. The bushmaster and Osprey both require minimal mechanical skill to install. If you can put a gas tube in, then you won't have any problem putting either in.
The shorter the barrel, the bigger the incentive to do something else. Still, if you are not going to be shooting a lot of rounds through it (by a lot I mean 10,000 rounds annually), I would suggest instead a compromise by using a hydraulic or spring loaded buffer for the 16" gun. This will slow the cyclic speed of the shorter gas tube, giving your magazine spring more time to feed the next round up. Might I also suggest using a Teflon lube instead of your standard CLP, as it goes on dry, thereby attracting less dirt.
If you have a s***load of money and want a gun that will fire until it glows with no malfunction whatsoever, I would suggest buying a POF upper.
I hope this helps you out. Safe shooting.

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