Help with M16 malfunction

[Theohazard]

https://gunsmagazine.com/buffer-stuff/

Carbine-length systems, in particular, can produce problems. Essentially, if too much [gas] gets in too soon, the bolt will unlock too soon as the system begins moving the bolt carrier to the rear. Then, the cartridge case gets yanked while it’s still expanded inside the chamber. This creates the “extraction” problems common to carbines (16″ or shorter barrel). It’s not an extraction problem, really, but a timing issue.

Additionally, an overdose of gas creates overly high-bolt carrier velocity going back against the buffer. It can get so high, and again this is most symptomatic in carbines, that the carrier will “bounce” off its rearward stopping point and rebound overly quickly, going back ahead.
[...]
We are in milliseconds with respect to “fast” and “slow.” Virtually all the influential firearms functions, including breaking a shot, are measured in milliseconds.

So, there is help for all this; altered port locations and sizes (only done on custom re-barreling projects) or regulated gas blocks—or both—make big differences. So, too, do heavier-weight carriers. Those resist initial movement for a speck longer, giving internal pressures longer to subside. The easier means are related to the “back part” of the system, which, let’s say, is the buffering apparatus. It can be altered to influence bolt carrier movement, in both directions. The direction that matters most is going back after firing.
[...]
Increasing buffer weight is effective. Doing this softens carrier movement rearward. The more weight, the harder to push.

 

[Theohazard]

Notice the extremely fast cyclic rate. Is that a sign of overgassing?

The more over-gassed your rifle is, the higher the cyclic rate is. So yes, that's definitely a sign of over-gassing.

That's one of the problems the military has when they add silencers to their rifles: The cyclic rate increases due to the extra gas back-pressure pushed back into the system by the silencer. That's one of the reasons that the military likes to use Surefire silencers; they're specifically designed to lower back-pressure, and one of the advantages of that is they don't increase the cyclic rate as much as traditional silencers.

 

[Mobuck]

"Increasing buffer weight is effective. Doing this softens carrier movement rearward. The more weight, the harder to push."

This failed to include that "the more weight moving, the harder it hits(as in the buffer hitting the back of the tube)". Bigger hammer--bigger impact.

 

[Theohazard]

This failed to include that "the more weight moving, the harder it hits(as in the buffer hitting the back of the tube)". Bigger hammer--bigger impact.

Sure, but when the force behind the heavier hammer is enough lower than the force behind the lighter one, the heavier hammer will have a lower impact.

When you have the proper buffer weight, your buffer hits the back of the buffer tube a lot more softly than when you have a buffer that's too light. And currently, Tony has a buffer that's too light. His bolt is unlocking too soon, and the carrier is going to the rear much faster because of two reasons: 1), the buffer is too light and therefore it moves faster, and 2) because the bolt is unlocking when the gas pressure is still super-high.

Adding a lighter buffer not only slows down the acceleration of the carrier, but it also allows the bolt to unlock a little later, and by that time the gas pressure has dropped a bit. So not only does a heavier buffer go the rear more slowly, but it also has less force pushing it to the rear in the first place. When Tony replaces his carbine buffer with an H2 or H3 buffer, it will hit the back of the buffer tube with a lot less force.

 

[Mobuck]

You know the way to answer these questions is to put some sort of device inside the buffer tube to determine how much the heavier buffer is slowed vs. a lighter buffer and how much force is exerted on the end of the tube. When these factors are given reliable numbers, the answers will be more than guess work.
I studied Physics in depth at an earlier time in my life and still remember parts of those studies. I think everyone will agree that a bigger hammer hits harder even though it's moving slower than a lighter hammer. Otherwise, the old timers would have been driving railroad spikes with a tack hammer(maybe a little stretch on the comparison).

 

[Theohazard]

I think everyone will agree that a bigger hammer hits harder even though it's moving slower than a lighter hammer.

Mobuck, did you not read my previous post or are you ignoring it? Or am I just doing a bad job of explaining this?

Your hammer metaphor is skipping over the fact that a heavier buffer allows the gas pressure to drop before the bolt unlocks. This means that the carrier and buffer move rearward with less force to begin with.

This is common knowledge in the AR world: On an AR with the proper buffer weight, the buffer will hit the back of the carrier with less force than it will on an AR with a buffer that's too light. Period.

 

[Theohazard]

You know the way to answer these questions is to put some sort of device inside the buffer tube to determine how much the heavier buffer is slowed vs. a lighter buffer and how much force is exerted on the end of the tube.

You don't need a device like that. Just experiment with a few different buffers. It's very noticable how much harder a lighter buffer hits the back of the buffer tube; you can feel it pretty easily. And you can see it when a buffer that's too light repeatedly gets battered by hitting the back of the buffer tube too hard. The buffer in Tony's pictures is an extreme example because it's in a full-auto, but I've seen that happen many times with a lighter buffer and I've seen the problem fixed when it's replaced with a heavier one.

 

[Mobuck]

Covering up the problem still isn't a solution. I still disagree that a heavier buffer is the solution if the problem isn't directly related to case rim damage.
The REAL problem is over gassing and the solution is adjusting the amount of gas.
Trial and error, guessing, analogies are worthless until the actual amount of change/difference is put on paper. Estimates, personal perceptions, or past experiences MAY work but technically may not be the correct answer.
Slow motion cameras are readily available that can be used to determine the exact amount of delay and even give a viable approximation of the bolt speed. Sensors could easily be located in the buffer tube to give exact figures on impact force.
Basically, until I see the numbers, I'm going to be skeptical of the answers.
I'm done.

 

[243winxb]

11.5 inch Colt LE upper

Why not Colt buffer parts to match the upper?

 

[Machineguntony]

Because Colt buffers are hard to find. Right now every website I can find shows that Colt buffers are out of stock.

I just ordered some buffers from Stagg Arms.

This gun is my favorite shooter M16/AR.

 

[Theohazard]

Covering up the problem still isn't a solution.

Of course it's a solution. As many of us have said repeatedly in this thread, there are two ways to address the problem that Tony is having: Either by lowering the amount of gas up front or by tuning the buffer system in the rear. Both are solutions that will fix his problem.

When the Army developed the M4A1, they had issues with the carrier moving too fast and they also had issues with bolt carrier bounce (since the M4A1 is capable of full-auto, these problems were a lot more noticable than they were on the three-round-burst M4). The Army's solution for this was to switch from an H buffer to a heavier H2 buffer in all M4A1s.

The REAL problem is over gassing and the solution is adjusting the amount of gas.

Sure, that's one of the solutions that many people prefer. To lower the amount of gas, Tony could replace his barrel with one that has a smaller gas port. Or he could remove his existing A2 front sight and install a less durable adjustable gas block that might have issues with adjusting itself under recoil. But instead he could simply buy a heavier buffer and fix his problem a lot more easily.

Slow motion cameras are readily available that can be used to determine the exact amount of delay and even give a viable approximation of the bolt speed.

Here's a slow-motion video of two different rifles tested with various buffer weights. Notice that the heavier buffers slowed the carrier down quite a bit on the rifle with the carbine-length system, whereas the carrier was already slower with the mid-length rifle and the addition of heavier buffers made less of a difference. Also notice the lower bolt carrier bounce with the heavier buffers; that's another advantage of using a heavier buffer (the heavy 9mm buffer still had lots of carrier bounce, but that's because its internal weights aren't reciprocating like on the other buffers).

Basically, until I see the numbers, I'm going to be skeptical of the answers.

There's a point in which skepticism becomes denialism...

 

[Theohazard]

Because Colt buffers are hard to find. Right now every website I can find shows that Colt buffers are out of stock.

Yeah, I discovered that when I was trying to find a heavier buffer to fix my overgassing issues on my new LMT SBR.

 

[Theohazard]

I still disagree that a heavier buffer is the solution if the problem isn't directly related to case rim damage.

But if there is case rim damage, that's a sign of the rifle being overgassed; the bolt is unlocking too soon while the gas pressure is too high and the case is still expanded in the chamber. In this situation the extractor is trying to pull the case out of the chamber too soon, but since it's still expanded against the chamber wall the extractor ends up damaging the case rim and sometimes even leaves it in the chamber.

So basically, in post #28 you're admitting that a heavier buffer can fix issues of case rim damage due to overgassing. And the reason it fixes that problem is because a heavier buffer slows the carrier down and delays unlocking, allowing the gas pressure to drop before the case is extracted. But you're also claiming that a heavier buffer doesn't fix overgassing issues and doesn't delay the bolt unlocking. So basically, your argument is that a heavier buffer is a solution for overgassing issues but it's not a solution for overgassing issues? That doesn't make any sense at all.

 

[Mobuck]

"So basically, in post #28 you're admitting that a heavier buffer can fix issues of case rim damage due to overgassing. And the reason it fixes that problem is because a heavier buffer slows the carrier down and delays unlocking, allowing the gas pressure to drop before the case is extracted. But you're also claiming that a heavier buffer doesn't fix overgassing issues and doesn't delay the bolt unlocking. So basically, your argument is that a heavier buffer is a solution for overgassing issues but it's not a solution for overgassing issues? That doesn't make any sense at all."

I said I was DONE but I can't resist this challenge.
A heavier buffer IS part of the answer to resolving RIM DAMAGE. A heavier buffer isn't the remedy for overgassing.
Are you at all aware of what momentum is? It relates to weight, speed, and applied force.
If you read any of the older books about shooting, bullet weight, and ballistics, you'll encounter theories of heavier, slower bullets projecting more force(power/energy) on target than lighter, faster bullets. Silhouette shooters quickly discovered that heavier but slower bullets knocked targets down better than lighter, faster bullets of same caliber.
While a lighter buffer accelerates faster at the beginning of the operating cycle, it also decelerates quicker when working against the buffer spring over time. A heavier buffer accelerates slower but retains it's speed(energy) longer while compressing the buffer spring. The momentum of the heavier buffer may increase the force applied at the end of the cycling stroke vs a lighter buffer.
The DI system isn't an instant application of force. The gas maintains pressure for an amount of time dependant of gas port size, location, "dwell time", powder type, bullet velocity-basically a LOT of factors.
I don't profess to be an AR "guru", I DO have considerable knowledge of physics, mechanics, and such which can be applied to the function of firearms.
There is no denying that a heavier buffer slows the cyclic rate due to it's resistance to directional change(inertia) at both ends of the cycle. There's also no denying that this weight increases the impact at both ends of this cycle. It's the laws of physics.
Now, I'm REALLY DONE. Thanks all for your patience.

 

[Theohazard]

A heavier buffer IS part of the answer to resolving RIM DAMAGE. A heavier buffer isn't the remedy for overgassing.

But rim damage is caused by overgassing <pounds head against wall>!!!

There is no denying that a heavier buffer slows the cyclic rate due to it's resistance to directional change(inertia) at both ends of the cycle. There's also no denying that this weight increases the impact at both ends of this cycle. It's the laws of physics.

Wow. For the 67th time: No, it does not increase the impact at the end of the buffer tube. Why do you keep saying this over and over and over again? It's simply not true, and it shows how utterly ignorant you are on this topic.

How many times do I have to explain that a heavier buffer delays the opening of the bolt, allowing the gas pressure to drop? That means that a heavier buffer goes to the rear with less force to begin with. Yet you keep ignoring this when you repeatedly bring up this argument.

The ridiculous thing here is that by admitting this delay helps resolve issues with rim damage, you're admitting that this delay takes place to begin with. I honestly don't know what to say to this; I already tried to explain it multiple times. I've provided several links that confirm what I've said. And the internet is full of many more reputable sources that further back up what I've said. And yet you're still claiming I'm wrong even though you've demonstrated that you don't have a very good understanding of how the AR works. Like I said before, there's a point where skepticism becomes denialism, and you seem to have passed it several posts ago.

 

[Hummer70]

Examine fired cases and see if you are getting evidence of the rim of the case being deformed by the extractor.

I had a 16" barrel one and the figured out the gas port in the barrel was too big. I talked to my engineering contacts at Rock Island and they told me the first run or two of the shorty barrels and the same gas port size as normal barrel.

They reduced the port size on later issues.

 

[243winxb]

M16A1- I read over at AR15.com that my 14.5" carbine had a larger gas port and different location then the smaller port 20" rifle of that vintage. Anyone know if true??

 

[Theohazard]

M16A1- I read over at AR15.com that my 14.5" carbine had a larger gas port and different location then the smaller port 20" rifle of that vintage. Anyone know if true??

It depends on the barrel manufacturer, but here's a chart that supposedly shows the standard range of gas port sizes for different barrel lengths:

Disclaimer: I don't know where this info came from originally, but I've seen it posted in enough reputable places online that I tend to think it's probably accurate. Also, I think the military specifications for gas post size changed from the M16A1 to the M16A2, but I'm not sure of that.

The best way to be sure you get the correct info is to sift through the actual technical specs for each type of rifle, and I don't have the patience for that at the moment .

 

[Machineguntony]

For some absurd reason, H2 and H3 buffers are out of stock at many places. There's a ridiculous buffer shortage. I could not find an H3 buffer that was in stock anywhere, so I ordered an H2 buffer that was allegedly in stock from Stagg Arms.

I'm going to call out Stagg Arms on this. I don't think their buffer was in stock because after waiting like two weeks, I finally got my H2 buffer today.

Anyways, I took the M16 to the range tonight and tested it. The gun ran beautifully with the new buffer. The rate of fire seemed much slower with the H2 buffer. It was also surprisingly much quieter with the heavier H2 buffer. It was so quiet that the guy a few stalls down thought I was shooting a 300BLK. The 'thud' of the bullets hitting the ballistic mat was the loudest sound component. Very pleasant to shoot. I had no idea what I was missing by not using a heavier buffer!

The top gun is an AR with an RDIAS that uses a standard buffer. The bottom gun is the H2 buffered M16.

My guess is that they both now have about the same cyclic rate, whereas before, the M16 was crazy fast (there's a video I posted in an above post).

 

[Sharkbite]

Good to hear....

Enjoy em!!