"Over Gassed" AR's Fact or Fiction? Other Perspectives
- Thread starter Flexible Tangerine Sprite
- Start date
For op to flex on us with all his experience but clearly be wrong in the end… some guns need gas adjustment end of story. Dude can flex all his military experience he wants but real world use tells a different story.
Sure guns spec’d with the correct port size for an appropriate application will not need any tuning. Others will definitely need tuning.
Didn't read the thread but will throw out my experience.
First off, I will concede that under-gassing or over-springing or over-weighting the buffer will cause more feed problems than over-gassing. You see this a lot in 3-gun and other comps where guys are trying to run the ragged edge and reduce recoil. That said, at some point, increasing the gas will 100% cause feeding, stove pipe, and ejection problems. Somewhere in the abyss I have high-speed footage that shows as much.
The lateral velocity of the ejecting case is pretty much constant and is determined by the ejector plunger spring and the ability of the extractor to properly keep hold of the case. As you increase gas, the rearward velocity component increases and the ejection angle changes, becoming more shallow. Eventually you start hitting the brass deflector (no big deal, still ejects 3:00-4:00), and then as you keep adding gas your cases smack the rear of the ejection port before they can clear the ejection port. This is when you start seeing 12:30-2:00 ejection. Keep adding gas and the cases will hit the rear of the ejection port then fly back into the upper. Sometimes you get extractor issues here, too, with the increased rearward velocity.
Bolt carrier velocity and the impulse of the BCG bottoming out causes a dynamic response to the rest of the system. Sometimes it's no big deal, sometimes, especially with sloppy magazine wells or lowers that hold the magazine at a lower height it definitely can cause feeding problems. The root issue is probably more the loosey goosey magazine well, but excessive recoil/gas isn't helping.
From an accuracy standpoint, I also have documented an increase in the frequency and the severity of fliers when increasing gas to the system.
I am firmly of the opinion that you want as little gas as is necessary to 100% function the system in the range of cleanliness/lube/temp/weather conditions you'll experience unless accuracy isn't on the priority list then gas it up to the point that you avoid the afore-mentioned function problems.
YMMV.
First off, I will concede that under-gassing or over-springing or over-weighting the buffer will cause more feed problems than over-gassing. You see this a lot in 3-gun and other comps where guys are trying to run the ragged edge and reduce recoil. That said, at some point, increasing the gas will 100% cause feeding, stove pipe, and ejection problems. Somewhere in the abyss I have high-speed footage that shows as much.
The lateral velocity of the ejecting case is pretty much constant and is determined by the ejector plunger spring and the ability of the extractor to properly keep hold of the case. As you increase gas, the rearward velocity component increases and the ejection angle changes, becoming more shallow. Eventually you start hitting the brass deflector (no big deal, still ejects 3:00-4:00), and then as you keep adding gas your cases smack the rear of the ejection port before they can clear the ejection port. This is when you start seeing 12:30-2:00 ejection. Keep adding gas and the cases will hit the rear of the ejection port then fly back into the upper. Sometimes you get extractor issues here, too, with the increased rearward velocity.
Bolt carrier velocity and the impulse of the BCG bottoming out causes a dynamic response to the rest of the system. Sometimes it's no big deal, sometimes, especially with sloppy magazine wells or lowers that hold the magazine at a lower height it definitely can cause feeding problems. The root issue is probably more the loosey goosey magazine well, but excessive recoil/gas isn't helping.
From an accuracy standpoint, I also have documented an increase in the frequency and the severity of fliers when increasing gas to the system.
I am firmly of the opinion that you want as little gas as is necessary to 100% function the system in the range of cleanliness/lube/temp/weather conditions you'll experience unless accuracy isn't on the priority list then gas it up to the point that you avoid the afore-mentioned function problems.
YMMV.
FWIW.... I worked on a CLGS 16", with a gas port size of over .100 ( biggest pin gauge I had. )..... guess what the problem was ?
The over sized gas port was breaking the hammer pin in half. The BCG was slamming it so hard !
The OEM one was broke in clear in half when I got it. I told the owner to get a proper gas ported barrel and I will replace it for him.
He and his buddies had all bought the same AR from the same local company... one by one, same issue 3X.
I agree with this. A vast majority of gassing problems are likely user induced. Too much buffer and/or too much spring.
For all of those guys out there that treat the AR platform as though they are playing with tinker toys, it's really handy to have a set of pin gauges. To say that you've assembled these parts and then post questions regarding which buffer and or spring to go with is almost like shooting in the dark (without NV). If you post those same questions with some information, like the size of your gas port, diagnosis would be a lot easier.
For common calibers, like 5.56, you can usually tell with a higher degree of certainty, what the proper buffer weight will be, if you know the gas port size.
I can confirm this, I've also seen high speed video of feeding issues on an over gassed system. Carrier velocities were way too high. When gas was reduced to bring carrier velocities into normal range, the feeding issues seen on HSV went away. No changes to action spring or buffer weights were made.
I can make an AR FTF by both over and under gassing the system. I think the OP's next thread will be "The Sky Isn't Blue".
"For the carpenter who's only tool is a hammer, all his solutions tend to look like Glocks"
(or something like that)
(or something like that)
I keep an open mind to learning new things so I keep waiting for the OP to say something profound, but I'm pretty sure he should sum up this tread and just come out and say that he's a dusty old curmudgeon that doesn't like all these new fangled AGB's and extended gas system lengths because "back in my day we didn't have all that stuff and we got along just fine!".
I figured: “I wanna run the spiciest of the spicy in 120 degree heat, suppressed…and when shtf, the crappiest steel cased puff load in Arctic conditions unsuppressed”
If it comes to it, I figure I can just throw a handful of Tula on the ground and the scavenger panic should be enough to allow for an escape...
My guess is Op isn't coming back with any real informative knowledge. I certainly don't claim to know it all by any means but even a smooth brain like myself, have remedied many an issue with an adjustable gas block or smaller id gas tube. That alone tells me that over gassing is real. Could something else contribute to the issue sure but if lower gas fixed it why waste anymore time or energy.
Reducing bolt failure issues is the reason to use AGB's as I understand it. Reduced recoil is an added bonus. Just about every problem with over-gassing relates to the bolt. Cam pins snapping, bolt lugs breaking early, excess fouling issues like stuck firing pins, stuck ejector plungers, carbon doughnut on bolt face screwing with headspace, etc. There's more benefits to using AGB's than not using them.
It's not really Physics when there are springs and weights involved in the equation. My thought after years of shooting supressed host AR15's it really depends on the rifle, port size, spring rate, buffer weight etc. etc.
Funny but using the buffer and spring method of the grail 3 o'clock myth is pretty simple really IME. It either works or it doesn't. Then the AGB comes into play. My 2c
Funny but using the buffer and spring method of the grail 3 o'clock myth is pretty simple really IME. It either works or it doesn't. Then the AGB comes into play. My 2c
Man, the claims of how many "ARs I've built" are getting out of hand on this forum.
Buy completed upper, buy completed lower. Slap together. “Built this Bad Larry all by myself.”
All of those things that you mentioned are true, but are also the long term side effects of overgassing. The more over gassed you are, the more prematurely parts will wear. Personally, I think that a bit of overgassing is a good thing and I'd rather be slightly overgassed than undergassed. It makes for a more reliable rig. The more immediate problems come in when you're too over gassed and you start getting stuck cases or even just torn case rims, as well as failures to eject. Overgassing can affect the reliability of a rig as well.
Well, it actually is physics, but you can come to conclusions through trial and error as well. Once you get to a point where it just works, you've found the formula. I know that If I'm putting together an 11.5" setup, I want to get to a .070 gas port and run either an H or A5H0 buffer with it using a standard spring. This will shoot well unsuppressed and only might require a bump up in buffer weight when going suppressed.
Or ... run the buffer weight and spring you want and tune to that buffer weight and spring with an adjustable gas block. The only downside to this is that those that don't understand what each component actually does could wind up with a rig that looks like it's running right, but it still too overgassed.
Part of the AR-15 cycle of operations involves an often-overlooked event where the bumper pad on the back of the buffer bottoms-out inside the RET, which contributes redirected momentum forward to facilitate more positive stripping and feeding of cartridges from the magazine into the chamber. Excessive cyclic rate can cause faster forward momentum.
Also, with excessive cyclic rate, the BCG can out-run the magazine spring’s ability to lift the cartridge stack quickly enough to present the case head high for the bolt to strip it, and you’ll see the bolt run past the head with the carrier face grabbing the case, and pinching the cartridge between the bolt and the feed ramps.
The biggest challenge is making an AR-15 that runs well in the hot when it’s clean or dirty, as well as in extreme cold when it’s dirty and keeping the gun running within the optimum cyclic rate window in all of those conditions.
Jim Sullivan said what they were always missing was adjustable gas, which could have solved all of this much easier like the FAL does.
The Crane O-rings were a band-aid for undersized chambers in the first production run of SOCOM heavy M4A1 barrels in the 2000s. Especially when suppressed with the KAC NT4, those guns would have FTExtract issues, so someone though the O-Rings would help with extraction.
The civilian side looked at this and said, “If SOCOM and Crane are using this, then it’s an upgrade we need to adopt in order to justify higher price points in our differentiation marketing approach."
Now it’s harder to find BCGs that don’t have them. They are totally unnecessary in a properly-chambered, properly-gassed AR-15.
Jim Sullivan: "The diameter doesn’t change, it’s the rounding off. There are two things about this event. The gas port in the M16, we didn’t know about this. A lot of the US gas operated guns, the BAR for example, had gas port adjustments on it. You can let the gas port be the initial throttle, but you can compensate for when it rounds off. But in a gas operated gun, if you don’t have a gas adjustment on there, you can’t use the gas port diameter as the metering diameter. You’ve got to go downstream someplace and put something smaller in there that can’t erode that remains the metering diameter.
We didn’t have anything like that in the M16, that part was our fault, we didn’t know it needed to be that way. I went to Colt about the M4, and took the plug that’s in the end of the gas tube and I moved it over this hole, and I made it the restricting hole diameter. No matter how big you make the gas port, or how rounded off it becomes, it’s the hole that is in the gas tube that does the metering and determines how much gas gets back here."
We didn’t have anything like that in the M16, that part was our fault, we didn’t know it needed to be that way. I went to Colt about the M4, and took the plug that’s in the end of the gas tube and I moved it over this hole, and I made it the restricting hole diameter. No matter how big you make the gas port, or how rounded off it becomes, it’s the hole that is in the gas tube that does the metering and determines how much gas gets back here."
Over the past couple of years, for many of the reasons stated, I've become a big fan of the YHM suppressor gas block. It doesn't have the flexibility of an adjustable, but it serves its purpose. At $18 each, although I can't do adjustments in the field, I can service a wearing rig to keep it running the best it can.
Right Tony agreed, but some people like to pretend an AGB is required which as you state isn't correct at least in the AR15/5.56 platform.
Both of my AR10 Armalites have AGB and without that it's not a very reliable platform while supressed ie; over gassed and it's obvious.
No supressor? AGB isn't required. Just like most .mil versions slightly overgassed is the most desirable aspect for reliability.
I also have a few 11.5's and they run as smooth as any but the spring/buffer rate is easily tuned.
AKs are built.
ARs are assembled.
Flame suit on.
-Stan
I'll see your shitty riveted commie guns "built" by babushkas and raise you with German delayed rollerlocks precisely crafted by the most stubborn people on the planet.
My 22-25 ejected at 3 o'clock before the suppressor and 1 after the suppressor. Turned the gas down and back to 3 o'clock. All the proof I need.
Ok, seriously....
When and more importantly WHY did the ejection pattern become the end-all, be-all sign of AR operation?
When and more importantly WHY did the ejection pattern become the end-all, be-all sign of AR operation?
Well, ejection pattern isn't the end all, be all gauge of proper gassing/closed bolt lock time; but, assuming that your extractor and ejector are working properly and you're running a standard spring rate, the ejection pattern is a pretty good indicator of proper gassing/closed bolt lock time.
You start messing with spring rate and that gauge pretty much goes out the window.
You start messing with spring rate and that gauge pretty much goes out the window.
I agree that it is a sign, but for me I don't really care where it ejects if it does so reliably. My favorite upper consistently throws them at 1 -1:30 but has done so for a couple of thousand rounds. At that rate I won't touch a thing.
Generally speaking, the ejection angle is the what you get when you add the ejection vector to the bolt rearward velocity vector. If your ejection vector is assumed to be pretty fixed/standard, then the variable is the rearward bolt velocity vector, and operating gas pressure is one of the main contributors to that.
Again, that assumes ejection (plunger/extractor interaction) is correct, and you can also affect it with buffer mass and spring rate, but the ejection angle is indicative of carrier velocity, regardless.
I can't find my "overgassed" video, but here's the rifle after installing an adjustable gas block. Before, with a standard gas block, the cases were smashing the rear of the ejection port and flying forward to 1 O'clock.
For many, it isn't an issue. Assuming all is well with the bolt, 1-1:30 is a sign of pretty aggressive gassing. As said, for many, it isn't as issue, as long as it keeps running with your chosen ammo.
So far, you've had reliability for 2000 rounds. Although overgassed rigs are generally more reliable than undergassed rigs, I'll bet your rig is seeing some pretty accelerated wear. Can you feel that groove in your cam pin yet? Notice some premature rounding on your bolt lugs? Ejector swipe marks on the brass? Perhaps partially torn rims on the cases?
Do you run steel cased ammo? Although your rig may be an exception, I'd lay odds that your rig chokes on steel cased ammo due to stuck cases.
I don't know how long you've had your AR or how many rounds you typically put through it, but for me, 2k rounds is a month of shooting and if I ran my setup that overgassed, I'd be replacing parts pretty often.
If you're considering going suppressed, I highly recommend some gas mitigation before doing so. Your rig will beat itself to death in pretty short order, if it runs at all.
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