AR15 malfunction: adjusting the rifle to the load.

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wildphil24

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Hi guys,

I have a Stag LH with round count of 900rnd, rebarreled 11.5". Standard carbine buffer, SA carrier.

I used to shoot Wolf cheap steel case. It's a low-pressure load. To avoid short-stroke, the carrier had to be oiled generously.

I made a big step-up and switched to 5,56nato. The recoil is twice stronger. Half the shots I have FTE. The empty case neck dive in the barrel extension or the front of the ejection port.

My understanding is that the bolt is traveling too fast under hi-pressure and the usual fix is a H / H2 buffer.
However I was wondering if a stronger recoil spring would give a better balance between the forces instead of increasing the inertia.

Why a heavier buffer instead of a stronger spring?

Thank you! :)
 
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Your first fix is to make sure your extractor spring has the "O" ring, when spent casing extracts but fail to eject completely out of the receiver.
 
I have a Wolff extra-power extractor spring with black insert. I didn't install the O-ring, afraid to over-kill it.

As you said the problem is Ejection. I never heard of weak Ejector spring?
 
Ejection spring is seldom the issue - failure to eject out of the receiver is mostly due to the timing of unlocking or excessive resistence in chamber or underpowered extracting force.

The cause of the issue is that short barrel AR unlocks much faster - as a result spent casing does not fully retract after expansion before extraction cycle begins. So either you have to give the extractor more grab with an extra power extractor spring or o-ring, or your gas port is too big. Also, a rough chamber will also cause this issue.

Make sure you have cleaned all the laquer or polymer crap left in the chamber by the Wolf stuff before shooting brass ammo.
 
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Thank you GreenTips.

Yes I scrubbed all the crap in the chamber, rifle is cleaned every shooting.

The carbine gas tube is the same than when I had a 16" barrel. Why would there be more pressure if the gas port is at the same location?

However you make me think I could misalign my low-profile gas block to reduce the input. But this might accelerate port erosion...

I ordered a Wolff extra-power recoil-spring. If it don't solve this issue, I'll get a H buffer.
 
There is no difference in the buffer springs among the carbines - I will give a H or 2H buffer the first go if you have already had extra power extractor spring - the H buffer is the standard for carbine.

A stiff spring gives a faster bolt velocity when the rifle returns to battery - bolt velocity needs to match with magazine spring rate. It is spec-ed for a reason.
 
Before you do anything, step back and take an overall look at the problem.

To start off, there is very little barrel after the gas port on the 11.5 barrel. This means that that once the bullet passes the port, there is very little time for the barrel to pressurize the gas tube before the bullet leaves the barrel and is lost out the muzzle.

Because of this, the barrel gas port on shorter barrels is enlarged to allow more pressure to flow into the gas tube and unlock the bolt. The problem is that the enlarged port produces very high action working pressure that has a high/quick spike and when the bolt unlocks, it does so violently.

Since now the bolt is unlocking while the barrel is still under high pressure, the spent case is still under pressure and the case is still pressure bonded to the chamber wall. This is the reason that the extractor slips off the case rim on the unlock cycle, and the use of an extra strong extractor spring or D-fender is used. A regular hardware plumbing O-ring of the correct size will also work in it's place.

Now that you have the bolt unlocking, getting the case out of the chamber, and the bolt/carrier full stroking on a A-2 butt stock rifle you are set. But if the rifle is a carbine, you have just run into the next problem, which is the bolt carriers speed is way faster than normal and the standard CAR buffer is having a hard time controlling the stroke.

Instead of the buffer stalling at the rear of the receiver extension tube, it is deflected and the return stroke is faster than normal. This leads to the bolt bouncing open on lock.

The way that a larger volume gas tube works is it softens the gas spike and since the pressure wave is away from the gas port, the tube will stay pressurized after the bullet leaves the barrel, and not fully drain back out the port. The stronger extractor force, applied by the stronger spring or D-fender, allows the extractor to pull the pressure bounded case out off the chamber walls.

A heaver buffer would allow the faster carrier speed to be controlled and lessen bolt bounce at lock time. Keep in mind that due to the lack of barrel past the gas port, there is very little operating pressure margin error. What is needed is the added barrel length after the gas port, or a device that will create the backpressure needed, like a suppressor, some kind of moderator, or compensator.

Bottom line is you want to slow the carbine's erratic action with your short barrel upper. You do that with a heavier carrier, heavier buffer and a D-fender on the extractor will have more grip without slipping off the rim while extracting a case still under certain pressure.

To avoid issues at the opposite end of AR function, you also need to make sure your gas key is staked on tight, the gas port is of the correct size, your gas tube is not obstructed in some way, you are shooting adequate ammuniton, and last but not least, make sure your gas rings are not excessively worn, nor aligned the same way.

A heavier recoil spring will do bupkis for you with or without any of the above.
 
A lot of 11.5" barrels have ridiculouly large gas ports. Many manufacturers make them big so they will cycle on reduce power .223 ammo.
Of course this can over drive the system when used with 5.56mm NATO ammo.

The "Crane" O ring or Defender is one of the best way to improve extractor tension.

When diagnosing Frankenguns, it usually best to start at the most common and cheapest solutions.

Extra power recoil springs and Hydralic buffers usually cause more problems than they solve.

The H and H2 buffer may sound cool, but bolt bounce (unless it is completely unlocking, and not going back into lock) is more of an issue for select fire guns, as the timing of the sear trip will cause the hammer to fall while unlocking and result in a click.

That said unless you have a very small gas port (unlikley) and weak ammo, it is not going to create more problems.

Most Gas Blocks have very large gas port holes in them, so you would need to really misalign the block to cause a reduction in the gas flow, and you will then bend the tube so the gas key will not slide over easily if you try to go that route.

Short Barrel DI guns are much more finicky than their larger counterparts, and cobbling together a Franken SBR is usually a PITA unless you do it with high end parts..
 
That's serious input.

So if I understand, a stronger recoil spring won't really slow the carrier backward but of course will accelerate forward, causing less reliable feeding. Guess I'll cancel the Wolff order.

By gas block misalignment, I was thinking forward or backward. So the tube is not bent but not at the same position in the gas-key. This seems hazardous.

I slowly understand why a heavier buffer is the way to go.
Would you suggest a beefier gas tube? It seem way less popular.
 
For different Gas Tubes; one solution is the PigTail gas tubes that LaFrance was doing, it give you rifle lenght tube that wraps around the barrel. I'm not a big fan, but its an option. The other option is a PRI FatBoy tube, the idea is it gives rifle tube volume in the short fat package. The problem is it necks down and directs higher pressure gas into the gas key. They work well on some guns, and miserably on others, depending on port size.

I like to stay away for those changes if I can.

Moving the gas block backward will cause issues with the carrier ket slamming into the tip -- not what you want. Moving it forward a few thousands can cause other issues, for not only now will you have a smaller port (which can be good in some situations) you will have lessened the engagement area of the gas key over the tube, so it will 'uncork' and bleed pressure faster.
Nothing good will come of that, if you want fir the gas port hole, you can drill it larger, and put in an Inconel plus with a smaller port in it, but unless you have a good machine shop that can do it, you'll have a ruined barrel for sure.

The other issue is you may have a .223 chamber in the barrel, and the 5.56mm ammo is really sticking in the chamber more than just obturation in that its getting kinda crunched a bit in there. If you have access to a 5.56mm reamer, and have someone competent to ream it, that may solve all your issues.

I get spoiled at work, as we have high speed video and some other stuff that we can track exactly what happens, so its easier than diagnosing third party issues on the net.

If you can spell out the barrel make - as well factory or remanufactured 11.5.
The type of ammo, and all the rest of the parts manufacturers it will make it easier to track down the answer for you.
 
I've had some experience with pigtails, gas ports, short stroking and all the goodies that cause extraction problems and erratic carrier behavior. I learned that pigtails cause more problems than solutions.

You don't hear much talk about pigtails because there are more controllable ways to solve AR timing problems.

Pigtails work by increasing the dwell time needed for the gas pulse to hit the gas key. A pigtail delays the unlocking time of the bolt and carrier without affecting the volumetric flow. It's a part cure for the bolt unlocking too early. (Volumetric flow are the key words here).

If the carbine's gas port is too big, the volumetric flow is too high and the greater gas velocity through a bigger gas port shortens the time required for the gas to reach the bolt group. A pigtail simulates this effect by increasing the travel distance of the gas impulse so it reaches the carrier to unlock the bolt at the correct time.

Because the correct timing is dependent on gas velocity and duration of gas supply, the distance from the gas port to the muzzle is important. When the bullet leaves the barrel the pressure subsides and the gas pulse is gone. If the distance between the gas port and the muzzle is too short, the volumetric flow will be affected and the carrier will short stroke.

You get better timing control with buffer weight, carrier weight and a heavier extractor spring, harder insert and a D ring installed. As I mentioned earlier, cartridge velocity, muzzle brakes, or compensators are also ways of control.

As for fat gas tubes, I've never played with one, but theoretically I don't think one would have any different effect than a pigtail. The gas port controls the volumetric flow.
 
Think like a water hose with a different nozzel shape -- the constriction of the nozzel affects flow as well, not just the size of the tube, and thus not only the gas port size is the constraining factor, the design of the gas tube plays a part.

The other problems with the PigTails, if they assume that giving rifle tube volume and length will solve the issue - and all else being equal it would, but port pressures at X are not the same as X-5.5", as well as the 'dwell' of the pressure will be different with a barrel with 3" past the gas port, and 8.5" past the port (just throwing that out there, I don't have the dimension in front of me), so they are basing the fix off junk science, and garbage in, garbage out applies here.

You could probably make a variable sized tube with crimps that expand and contract gases and redirect them to slow it down (much like suppressor baffles do with sound/shock waves. But then again you could build it right to begin with.
 
KevinB said:
If you can spell out the barrel make - as well factory or remanufactured 11.5.
The type of ammo, and all the rest of the parts manufacturers it will make it easier to track down the answer for you.
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It's a factory barrel (not cut-down) from unknown brand marked only: 5.56 nato 1-9. It's wearing a Dlask Vortex-like FH. Gas block is YHM-9384. Troy MRF rail. Wolff extractor spring. Standard carbine buffer.
For our concern, all the rest is Stag 2HL.

I cancelled the Wolff recoil spring and will look for a H2 buffer.
 
I will bet gas port sizing - whoever did the cut job will have to adjust the gas port size accordinginly. Not every gunsmith knows to do it properly.
 
I am a big fan of extra buffer weight.

I did an experiment with additional buffer weight and much to my surprise the 11.5" DPMS barrel I was using allowed me to more than triple the buffer weight without causing any kind of feeding or lockback problems.

I went from the standard buffer's 85gm all the way up to 310gm and the rifle still cycles and locks back perfectly with Am Eagle 55gr ammo.

I had expected at some point the rifle would simple stop cycling properly but that never happened. One thing I did notice is that the recoil impulse is much softer. I am sure the cyclic rate is way down but in a semi-auto who cares. Seeing as most of us have large sums of money tied up in these rifles, it makes sense to reduce the battering they take with every shot. A heavy buffer is a cheap way to accomplish that.

It is all well and good to talk about oversized gas ports but how do you make a hole in a piece of metal smaller? An inconel plug is fine for KevB to discuss but few people up here are going to be able to arrange that kind of fix, and even if you could the cost would be much higher than replacing a buffer making it pretty much a moot discussion on our part.

I'd suggest getting hold of a 9mm buffer (the heaviest buffer that will be inexpensive and easy to come by) and try that.
 
Suputin said:
I went from the standard buffer's 85gm all the way up to 310gm and the rifle still cycles and locks back perfectly with Am Eagle 55gr ammo.
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:eek: 310 grams? Are you sure about that? That's about 11 ounces. Wow, what kind of buffer is that? :D

An A2 buffer is only 5 ounces. A 9mm buffer is about the same, maybe 5.5 ounces. The heaviest buffer I know of that doesn't even come close to your 11 ounces is the Enidine hydraulic rifle length buffer at 6 ounces, I think. :confused: Maybe I'm wrong, I had a hard day at work today.

Suputin said:
It is all well and good to talk about oversized gas ports but how do you make a hole in a piece of metal smaller?
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In such a situation variable adjust gas blocks are an option.

I believe in the OPs interest, installing a D ring atop a heavier M16 extractor spring with a black insert would be the best conclusion.
 
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310 grams? Are you sure about that? That's about 11 ounces. Wow, what kind of buffer is that?
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Yes I am sure, I weighed it on a postal scale. I custom made my own buffer and maxed out all the dimensions so it could contain as much metal as possible. The weight is a big chunk of carbide salvaged from a broken endmill. Much heavier than steel.
 
Suputin said:
Seeing as most of us have large sums of money tied up in these rifles, it makes sense to reduce the battering they take with every shot. A heavy buffer is a cheap way to accomplish that.
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The total amount of energy in the system is the same as long as the spring is the same. The spring is not going to store more energy because the buffer is heavier - the law of energy conservation.
 
I would say that your port on your 11.5" Didn't Pass Military Spec barrel is outrageously large, if it is still running with a buffer that heavy.

Keep in mind the M16FOW does not operate on runout - the Buffer does impact the rear of the buffer tube/recevier extension.

With a heavier weight you can slow the speed of the carrier, and all else being equal will have slowed down the impact velocity. Thus perceived recoil to the shoulder is decreased, as you have taken energy earlier in cycle.

The best way to observe this is with a cutaway system and highspeed video, as you can plott the carrier velocity over time, and make a very nice chart of the entire cycle.

However the heavier buffer you do put in, the return impact is that much more, so thinking your saving you bolt, by adding an additional buffer weight is incorrect (for the most part).
 
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