Gas system question

[Txbonecollector75]

My ar-15 is made by Diamondback firearms it's chambered 5.56 NATO, it's a low profile gas block, and is carbine length gas system. When I shoot certain brands of ammo like PPU, aguila, or any ammo that's 5.56x45, it's damaging the head of the cases. Some people have told me I need to clean my chamber and bore or clean my gas system , but I clean my rifle after every trip to the range, and some have told me that my gas block is either over gassed or under gassed. And I have inspected the gas system when I've taken it off of the barrel, the gas block fits correctly over the port in the barrel. Is the port for the gas block and gas tube supposed to be the same size and match up or how much of an opening is supposed to be between the block and tube?

Has anyone else ran into a problem like this with the case head being damaged, and if so was it something to do with the gas system or something else?

[CarJunkieLS1]

Pictures of the case head would be very helpful...

[Metal god]

Yeah pictures and where is the cases being ejected to , 12 to 3 o clock over gassed 3 to 5 correctly gased

https://www.google.com/search?client...1Lfp14M3f-M%3A

When they say its the gas system they are just saying its ejecting the case in such a way that the mouth of the case is hitting the shell deflector causing the ding .

[stagpanther]

"head" is a bit overly broad--do you mean base, rim-face, web--etc--and also what type of damage are you talking about?--these things get cycled pretty dynamically so a certain amount of beat-up is expected. Things to REALLY worry about would be things like case bulging--deformation in primers and generally significant changes in case dimensions (though a bit of neck flow or shoulder bumping isn't abnormal either). A case gauge can help with that.

[Txbonecollector75]

I only have this one case left from those rounds, and I looked at the chart and sometimes they are landing in the 3-5 position but some are landing in the 5-6 position, and I can see on my gas tube where it looks like I'm getting blow by from the gas block. How do I fix the leak at the gas block

[marine6680]

The gas leak is fine, it will self correct as carbon builds up in the gap... It's obviously not causing a function issue.

While your term "damage" is vague... I would bet you are over gassed. It leads to damaged rims from the extractor, and smears/swipes on the case head from the ejector.

All ARs are over gassed to a point, and carbine length gas systems are the most notorious for it.

Get an H3 buffer and try that.

[Txbonecollector75]

And this is the only shell case I have left and it blew the primer out as well that day.

[marine6680]

Pic is blurry, but it looks like you have swipes on the case head.

The fact that is blew a primer... Early extraction with pressure in the chamber? Possible head space issue? Anyone else have an idea there?


I still suggest an H3 buffer. And double check the barrel is marked 5.56.

[Reloadron]

If you watch an AR15 extraction and ejection process in slow motion (about 1200 frames per second) you can see the normal process is pretty violent. When a rifle is "over gassed" it gets much more gas than it needs for normal extraction so the bolt carrier group really yanks on the case head dragging the case out of the chamber violently. When this happens in any gas operated rifle something has to give and the soft brass of the case head gets ripped up a little or in some cases a lot. The higher the pressure of the ammunition being shot, the more violent the extraction process. Some ammunition will have higher pressure and subsequent more and faster gas pressure than other ammunition.

Based on your fuzzy image and description that would be my guess as to what is going on.

Ron

[stagpanther]

I'm guessing you have a combination of over-gassing (very common with "commercial grade" AR's) and a possible pressure spike due to improper chambering of cartridge.

To help a bit; here's a quote I borrowed from ARF.com https://www.ar15.com/mobile/topic.ht...&f=66&t=235071:

"Tweek, you must get tired of this stuff. I am sure that most of this is in the FAQ's.

Short answer is either do not use the ammo that gives trouble or put in a new good barrel chambered with a 5.56NATO reamer.

I keep seeing the same things in these threads, so let’s get some things straight:

Excess pressure is generally caused by three things (in combination) - powder in the case , throat/barrel dimensions, throat/barrel condition;

Inadequate headspace and too small chamber body diameters cause rounds to not chamber and may have a puny impact upon pressures. The case just does not expand as much as normal, but this effect is really small ;

Excess headspace can result in flattened primers (the case is shoved forward by the firing pin strike, leaving a space between case and bolt, then the primer backs out under its presssure to fill that space, then the case slides back under powder gas pressure flattening the primer), but usually means that case life (if you reload) will be short and you might get a head seperation, which is potentially dangerous! Pressures will actually be lower than standard, but the problem here is not pressure, it is that the case is streached too far and breaks.

Two chamber dimensions contribute to big chamber pressures - Neck diameter and neck length, and these only when they are the same size or smaller than the neck of the cartridge. They contribute to pressure by restricting the departure of the bullet, slowing the expansion of the powder gases. How to check? Simplest way is to check that a new bullet will drop through the neck of the fired case. It should, and if it does not, either the neck walls of the case are thick or the chamber is tight there. Get out a dial indicator and measure the fired inside and outside neck diameters and compare them against chamber drawings and bullet diameter.

The other chamber dimensions, like headspace and body diameters have puny effect on pressures because they do not change the volume enough to matter. So, no more citing headspace when diagnosing excess pressure! Got that? Measure neck diameters and report those.

Next, throats matter a bunch. GI/NATO throats are large in diameter and long, and should be what you find in a barrel marked 5.56 NATO. They will develop less pressure with a given batch of ammo than just about any other throat because the bullet travels more freely early in the firing cycle. Commercial rifles marked 223 Rem will usually have a SAAMI throat, which is shorter and the cylindrical portion is usually the same size as the bullet, which is generally more accurate and gives more pressure with given ammo. After that, you get into match throats, and there are both long and short. What is present in this rifle, in terms of chamber, neck, and throat dimensions is best found by taking a chamber cast (Brownell's and Midway sell chamber casting alloy for this purpose) and measuring it.

A really rough and/or contaminated throat (LOTS of jacket material and primer ash)can raise pressures. Copper solvents and JB bore cleaner will take that stuff out and should be used every few hundred rounds no matter what the duty on the rifle...

Last is the rifled bore. If it is small, it can cause higher pressures, but it usually is a small actor.

Now, on to the rest of the issue on this thread... If only one batch of ammo is giving trouble, and only in this rifle, "Doctor, doctor, it hurts when I do this" "Well, don't do that. That'll be five dollars" The ammo is too hot for your gun. Either send the ammo to the maker and complain, or sell it to someone who has guns that like that ammo. It really is that simple.

Now if not just that batch is hot in this rifle, but other batches of commercial ammo too, you have a gun problem, most likely the throat or the neck. If it is a steel or stainless steel barrel with no chrome, a gunsmith can apply the correct reamer to the barrel and your problem should be solved. In an AR15 that you are feeding whatever you happen to find, that should be the 5.56 NATO reamer. If you are willing to chack ammo and reject any that acts up, but still want miltary grade ammo to be acceptable, the Wylde chamber should be OK, and you can still go back and put the 5.56 NATO reamer in if the Wylde chamber is not enough.

If the bore and chamber have a coating of hard chrome, you are back to having to find out what ammo the gun likes, and only use that. Hard chrome is quite a bit harder than chamber reamer steel, so you will likely ruin a $50 reamer rather than fix the chamber. Perhaps there are some titanium nitride or cubic boron nitride coated reamers, and then you could theoretically fix it. You could pull the barrel, take a chamber drawing and the barrel to a tool shop and have them center the barrel and CNC grind the chamber to dimensions, but that will cost way more than a new correct barrel will.

Many people are concerned about the chrome layer peeling, but that is not actually the problem it is made out to be. Chrome and steel have very high affinity for each other, so if it was done right, it will staty put pretty well. Eventually the chrome is flame blasted away at the throat anyway, and then the throat wears normally until accuracy falls off and the barrel is replaced. If you find a way to fix a chrome chamber that takes off chrome, this process will proceed anyway. Remember, a chrome moly or stainless barrel without chrome that is cleaned regularly (without damaging the throat or crown) will give good match level accuracy to between 4000 and 7000 rounds anyway.

So, find a customer for ammo the rifle does not like and use only ammo that it does like, or replace the barrel with a good GI spec barrel. Clean it. The other stuff is academic and interesting, but otherwise not of much use. Good Luck!"

[Metal god]

Sorry i totally misread the op and thought it he was talking mouth of case not head . I cant see the pics do to blur so i cant see the mark .

Excess pressure is generally caused by three things (in combination) - powder in the case , throat/barrel dimensions, throat/barrel condition;

Stag , although that was all kinds of info i disagree over gassed AR's are caused by any chamber dimension . I also disagree that a 5.56 chambered rifle will have less pressure on the whole then a 223 . In certain instances the 223 will have higher start pressures but that does not mean the pressure in a 5.56 chambered rifle wont reach the same peak pressure as the 223 . Then there's the powder burn rates that will cause the peak pressure to be further down the bore resulting in higher pressures at the gas block . A classic example of this is the M1-Grand needing powders with a specific burn rate or they can be over gassed at the gas port and damage the gas system .

I guess my point is there are many reasons an AR can be over gassed . How ever chamber dimensions would be well down on the lift if it made the list at all . High on the list would be dwell time , port size and ammo .

[marine6680]

Yeah, chamber dimensions are not likely the cause of over gassing.

Excessive head space can be the cause of the popped primer, but I don't want to single that out yet, as it would need to be very out of spec I think. And likely to cause damage to the case at the neck/shoulder area.

I would bet the over gassing is a simple combination of gas port size and gas system length.

I still think that is the most likely culprit given the info we have so far.

[stagpanther]

As far as I know--over-gassing is a separate issue from over-pressure. Over gassing is a function of how your weapon handles the ignition exhaust through the barrel gas port--tube--carrier key etc and so on. The OP's case picture, as far as I can make out, seems to show signs of over-gassing in that it likely did not have enough dwell time in the chamber to be "relaxed" before the extractor yanked it from the chamber, deforming the rim. Hard to tell from the blurriness though.

It takes some pressure build up to blow a primer out (though it's possible it was simply loose) and I too thought improper headspacing might be a cause--I would expect to see some dimensional deformation in the case head area if that were the case-again--hard to tell just from a blurry picture. I quoted the guy from ARF because he raises another possibility for what might be a pressure-spike source. I only mentioned it as another possibility.

Even holding my own builds in hand for examination--it often takes me a while of sleuthing to figure out the cause and effect of cycling issues--but I'm not the sharpest pencil in the box. ; )

[marine6680]

Yeah two different issues... Though an over pressure could cause some over gassing.

I think it's ore likely to be simple over gassing typical of carbine length gas systems on a 16in barrel AR.

[Txbonecollector75]

Yes my barrel is stamped 5.56, so I'm not shooting 5.56x45 ammo in a rifle that's chambered for 223 or 223 wylde. And when it was deforming the rim of the head I was shooting Federal American Eagle, Fiocchi, AGUILA, PPU and it was doing it to the 5.56 NATO ammo and to the .223 Remington ammo. But when it was doing it the barrel was brand new and only had about 150 rounds through it, so not sure if that would be a factor or not. And I'm sorry about the blurry pictures but they said the pictures were to big so I had to shrink them and it blurred them a lot. As far as dwell time I measured from the center of the gas port on the barrel to the muzzle and it's about 9", on this 16" barrel.

And as far as the primer part it wasn't loose but the rounds were out of spec, the case trim was @ 1.778, and the powder charge was @ 29.1-30 grains of powder. And that was 5.56 AGUILA ammo, and I did receive a refund on the ammo.

And how can you solve the over gassing, do I need to put in a heavier buffer or a different gas block?

[Mobuck]

If over gassing is the problem, an adjustable gas is the answer.
A heavier buffer just camouflages the issue. The heavier buffer MAY slow the cycling enough to reduce the brass damage but is not a cure for the real problem.
I think you're having an over pressure problem and the result is more apparent with the softer brass used in those factory loads. The problem may stem from an out of spec chamber throat, rough bore, or other mechanical issue.

[stagpanther]

I've said it a thousand times on a thousand forums--why spend a bucket of cash on a new weapon only to fire junk ammo through it? Each new weapon I build is "my new girlfriend" and I break her in with diligence and care.

Time for my psychotherapy appointment....

I've used the adjustable blocks on a couple of builds--specifically JP's--and had a very hard time keeping the adjustment screw in place--even when held with strong thread-locker they seem to back out eventually at which point it's the same as starting off with a regular low pro. I'm interested in finding an adjustable block that has an adjustment that is truly robust with a beefy bolt to mechanically lock it--but is also accessible without having to remove the handguard. That's a tall order--any ideas Mobuck?

[Txbonecollector75]

how do you check for those problems that you listed so far? And what other mechanical problems could it be? Or would swapping out the barrel for a better quality barrel do better?

[stagpanther]

how do you check for those problems that you listed so far? And what other mechanical problems could it be? Or would swapping out the barrel for a better quality barrel do better?

This is again a fairly broad question--and in my opinion nearly impossible to accurately diagnose via internet forum--but here's what I would do:

1.First--I'd call the manufacturer and see what they say--you paid good money for their firearm and how they respond is a good indicator of their confidence in their product. They may blow you off with the "you used not recommended ammo" dodge--in which case you may be wasting your time.

2. I'd carefully examine your cases and look for tell-tale signs of over-pressuring--what you need to establish as quickly as possible is if in fact your weapon is even safe to use. Before and after measurements with a case gauge and a headspace check will probably give you some idea if you have a situation that could cause a pressure spike. It's not a good thing finding out your weapon is a hand grenade by continuing to fire it if it has a real problem. If you spend some time googling and looking at reloading manuals you can quickly learn signs of over-pressuring. If you're not comfortable with figuring this stuff out on your own--take it back to who you bought it from and ask them to test and establish the weapon is safe--in fact, you may want to do this anyway.

I build my own AR's --so when something like this happens I expect to figure it out on my own. When I buy a complete weapon, I expect (though frequently don't get) a weapon that should function safely and reliably within a reasonable range of parameters--if it doesn't I have no shyness about going after the manufacturer/dealer.

[marine6680]

As far as resizing pictures... MS paint actually does a decent job, it has a resize function. And I have used apps on my phone, but some are better than others, and I try to use a combination of cropping and resizing to get a small enough file size.

Also, keep a master copy of the pic to work from... If you shrink a pic, only to find its still too large, then shrink it again... You are basically making a copy of a copy, as the compression algorithm degrades an already degraded image.


As far as the rifle goes...

If the problem is over pressure, then the manufacturer will need to fix it, or a new barrel will need to be put on if they refuse. Inspect your brass carefully for over pressure signs, and if need be, keep several examples to send to the manufacturer when you send in the gun for repair if it comes to that.


If you can not find obvious over pressure signs on the brass, it may be simple over gassing, but as was said, it's hard to diagnose issues through pics and forum posts.

If the problem is over gassing, a heavier buffer may help. Heavier buffers help when the over gas isn't too bad, but if the problem is more severe, then an adjustable gas block is the proper solution... Or a barrel without an oversized gas port... And/or a midlength system.

Heavy buffers are just easy for anyone to try and it voids no warranty to use one. Swapping other parts may be a point of contention with the manufacturer. (Minus wear items like springs)

Throwing in an H3 buffer would be the quickest thing. If it helps reduce or stops the problem, then you know it's simply a gassing issue, you can then go from there.

[Txbonecollector75]

Ok, and I've been reloading my own ammo for about 3 months now and it hasn't been showing any signs of over pressure or marking up the case head and rim since I've started reloading, the only thing it's still showing signs of is where the extractor grabs onto the case rim and kinda imprints on that area of the rim. It also hasn't been tearing up the head or rim of the case since I've stopped using factory ammo.

And I do know my chamber measurement, I used a Hornady case gauge and it showed from the bolt face to the lands it's 2.352", and most of my hand loads are 2.200"- 2.260", depending on bullet weight.

I've already got an H3 buffer and new spring, so I'm going to put it in and try that first, to see if that works if not I'll get me an adjustable gas block. I'll start there before buying a new barrel.

[bfoosh006]

Sounds like you have plenty of freebore. Important, in a 5.56 chambered firearm. That free bore kind of acts like a little more case room for the ammo to use prior to building up full pressure. ( Weatherby rifles have a TON of freebore, for this very reason. )

If the H3 and new spring doesn't help enough.... I would suggest an adjustable gas block as well.

Ultimately ( it sure sounds like ) your rifle is getting to much gas from its current setup.

A heavier buffer and spring will help "slow" ( milliseconds ) the case's extraction. Allowing a little more time ( and less pressure ) for your case's to release from the chamber walls.... easing extraction.

An adjustable gas block, helps cut back the amount of gas sent down the gas system, to cycle your BCG.



I do have to ask... how hot was the factory ammo ? I mean was it sitting in a hot chamber or in the sun ?

[Txbonecollector75]

No the factory ammo was stored in one of my ammo cans always kept in a temp controlled room and was not taken outside till we were ready to shoot, it was a cloudy day when it first happened so it wasn't in the sun ever. The only thing I could think of was that the rifling was new and hadn't had a proper break in period so it caused some pressure spikes. But the AGUILA 5.56 ammo when I pull the bullets the rounds were double charged that the powder in some was sitting at the top of the shoulder of the case. The case length was trimmed to 1.778" & 1.779", and the only thing I can think of is when it chambered it pushed the crimp into the chamber so much it extra crimped it. But since I've been reloading I haven't had any pressure spikes, pressure signs in the case, and it hasn't been tearing up the case head, but should I go with an H or an H3 buffer and spring? Will the H3 be to heavy and not let it cycle properly?

[bfoosh006]

I doubt a H3 would not allow the carbine to function... maybe not 100% with underpowered ammo ( Wolf, PMC Bronze )

But... given your carbine gas length you should be fine.



Another way to go might be the Tubbs carrier weight system.

You can easily add or subtract weight with it.


Adddd.... it appears to be no longer made.

I own quite a few of those, and love them.


This chart helps show the port pressure curve with a M4 v. rifle length gas system.
The earlier the port pressure, the higher the pressure.. and the more "violent" the extraction..... so by adding weight to the recoiling mass ( BCG , Buffer , and in a certain sense... a heavier recoil spring.... you slow down the extraction. ( In overly simple terms )

As others have said ... you are kind of "masking" the real issue.

To much port pressure.

It works for a lot of people.... I have tuned all my AR's to have soft recoil, and 4:30 ejection.

[marine6680]

You can't go by volume on unknown powder.

The type of powder used may mean that 20gr of one powder requires more volume than 20gr of another.

Also the actual charge weight in grains will vary as well between powder types.


I doubt all the brands you tried that had the problem would be due to poor charge or excess case length.


And from further information that you posted, I'm inclined to think that it is over gassed for 5.56 ammo.


Most users of budget ARs also purchase the cheapest ammo they can find, which is usually not 5.56 spec... And often times steel cased. And the powders used in cheap Russian ammo has some odd burn characteristics that make it not function well in some ARs, especially those that are tuned to standard loads from domestic manufacturers.

So AR manufacturers are incentivised to over gas, so that cheap ammo will run well, and they get less warranty claims.

Most users would never look at the fired brass to even know a problem existed... If they even knew what warning signs are on fired brass.