AR gas question

BenL · Dec 11, 2017

I'm having cycling issues with a 10.5" Noveske 300BLK.

I occasionally get doublefeeds when shooting unsupressed (spent casing doesn't extract, next round rams into it still in the chamber.)

- I've tried every buffer from Pistol to H3; same performance from all. (Noveske recommends H2.)
- The buffer spring is the spring that came with the Phase 5 pistol buffer kit
- Gas key and rings function (tested with an air compressor)
- extractor looks fine
- ejector looks fine

With a single round in the mag, the bolt DOES lock back on the last round.

Does this mean that the gas system is fine and it MUST be either the extractor or ejector?

outrider58 · Dec 11, 2017

The spent cases are staying IN the chamber all the way, not half in/half out? Have you tested the extractor?*Remove extractor from bolt. Drag extractor claw across your arm. Did it leave two faint scratches on your skin?*

Does the Noveske have a "Switch block" gas block?

iH8DemLibz · Dec 11, 2017

Swap out the bolt and see if the problem disappears.

BenL · Dec 11, 2017

it looks like the round is slamming the spent casing back into the chamber, but yes, it's all the way back in the chamber.

No Switchblock- it came with a matched pinned block.

I'll take a closer look at the extractor and ejector. The more I think about it, the more all signs point to extraction/ejection as the issue.

BenL · Dec 11, 2017

iH8DemLibz said:
Swap out the bolt and see if the problem disappears.

Yeah, it would probably be easiest test, at this point.

outrider58 · Dec 11, 2017

BenL said:
it looks like the round is slamming the spent casing back into the chamber, but yes, it's all the way back in the chamber.

No Switchblock- it came with a matched pinned block.

I'll take a closer look at the extractor and ejector. The more I think about it, the more all signs point to extraction/ejection as the issue.

It could be a few things, but we take care of the easy things first.

Melnic · Dec 11, 2017

Here is an interesting vid to watch.

outrider58 · Dec 11, 2017

BenL, if you try another bolt group and it works, switch extractors and see if the good bolt fails, then you'll know it is the extractor or extractor spring(if there is a 'doughnut' on the spring, take it off). If you have a lot of rounds through that gun, you should check the ejector spring as well. They will break and encoil around themselves, resulting in shorter(weaker) springs.

holesonpaper · Dec 11, 2017

iH8DemLibz said:
Swap out the bolt and see if the problem disappears.

So I agree with others... Swapping out the bolt (or complete BCG) would be my first step. That's likely it - but if thats not it then look ammo (brass/steel). I have a Noveske 300BLK 10.5" barrel that eats pretty much anything I put through it. With that setup, the only issue you may encounter is the BCG not locking back on subs without a suppressor.

BenL · Dec 11, 2017

Melnic said:
Here is an interesting vid to watch.

Yup, I think that's what's going on with my rifle. I have a few spare bcg's laying around, so I'm going to put one of those in and see how it runs.

Sent from my SM-N920V using Tapatalk

GuitarmanNick · Dec 11, 2017

If you do not find a problem with the extractor or the bolt, I would suggest looking at the gas system. I know you said you tested it with compressed air, but if it is short cycling it would act as you describe. One thing that is often overlooked is the size of the gas port in the barrel. It may not have been drilled properly and could be limiting the gas getting to your BCG. This is supposed to be rare, but I have seen it happen and I have only been into AR's for about a year! Worth a check to save some headaches.

hotdog · Dec 12, 2017

^This^...or check the gas block, you might be having a loose gas block.

Sent from my iPhone using Tapatalk

John from MD · Dec 12, 2017

It's not short stroking if it is jamming another round into the chambered case. No sense debating anymore until he tries a new bolt.

outrider58 · Dec 12, 2017

John from MD said:
It's not short stroking if it is jamming another round into the chambered case. No sense debating anymore until he tries a new bolt.

^^^This^^^

GuitarmanNick · Dec 12, 2017

A few questions...
Has the gun ever run reliably?
If so, did you make any changes prior to the problem?
What do your spent cases look like?
Are they shiny or frosty looking? If the latter,... clean your chamber! A dirty chamber increases resistance when extracting spent cases.

I still suggest looking at the barrel's gas port if the chamber is clean and the extractor is good. Gas system flow being too low can cause the exact condition that you have described. This is especially true is you are not getting the bolt to hold open on the last round. Assemblers sometimes leave them loose or do not have them properly aligned and manufacturers sometimes have a defective part get through their quality control measures. Larue missed an undersized gas port on an $1100 upper even after it was sent back to them twice with complaints that it would not feed and was unreliable! The owner figured it out after 6 years of trying everything else he could think of after resigning himself to the fact that he paid way too much for the upper! He finally took a hand drill and drilled the port to a slightly larger size resulting in the gun running reliably for the first time. It will now eat any ammunition he feeds it without failures.

Routine cleaning of an AR usually does a good job of cleaning the gas port and few take the time to actually disassemble the upper and check it. It is also possible that there is a partial obstruction in the port or gas tube.

If after swapping bolts, cleaning the chamber, etc... you are still having issues, tear that sucker apart and make sure the port is clear. If the gun has never run reliably, check the port size!

DevinRPD · Dec 12, 2017

had the exact same problem with my 9 inch 300blk.
originally was using a semi-auto bcg and it ran perfectly. bought a new upper and put my spare full auto bcg and it malfuctioned the same way yours did every now and then.
i put the semi-auto bcg in the new upper and it worked fine.
concluded that it wasn't the lower or the mag. concluded it wasnt the gas system. i figured it was ejector or the dimensions of the bolt.
so i bought some replacement parts and polished my bolt and its been running fine since then

outrider58 · Dec 12, 2017

Some interesting reading from Noveske's site regarding 300AAC lo pro block barrels.

Barrel installation should be performed by a qualified gunsmith. Installation of the gas block taper pins and gas block is required to complete the assembly process.

All NFA Regulations apply. Please check your local and state laws before ordering.
Contact your local ATF Field Office with any NFA questions you may have.

Noveske’s 300 AAC BLACKOUT is designed to run optimally firing both subsonic suppressed and supersonic unsuppressed. This barrel is tuned to lock back on the last round using subsonic 220 and 208 grain ammunition with a sound suppressor. The firearm may not lock back with subsonic 220 and 208 grain ammunition without a sound suppressor. Also, the subsonic 300 BLK ammunition is more susceptible to a malfunction due to carbon fouling and adverse conditions than supersonic ammunition. The barrel is tuned to operate correctly with the back pressure provided by the AAC 762-SDN-6 using an H2 buffer, or a Surefire 762K suppressor and an H buffer. In the development of this barrel, we found evidence that the suppressor may require a symmetrical baffle stack as found in the AAC Cyclone K, 762-SDN6, and Surefire 762K suppressor. Suppressors which cause off axis turbulence, such as those with K type baffles, may cause baffle strikes and/or point of impact shift, and may damage your suppressor. Noveske Rifleworks LLC will not be responsible for damage or injury under ANY circumstances. Consult you suppressor manufacturer to determine if your suppressor is suitable for this application.
You can add a headspaced bolt to your barrel for $65, click here

clandestine · Dec 12, 2017

Lots of factors here. Outrider has said all that I would have said.

I'll add that gas key bolts can be a problem. To test them you use reverse inch pound torque at 30in# if they move the bolts are undertorqued or broken which will allow has to leak.

An oversized Gas Key or a worn Gas Tube can allow wear as well.

Are you using a one piece gas ring? If so ditch it.

If it were me it would get a Tubb Ejector Spring or Brownells CS Ejector Spring, and a New Colt Extractor and Colt Gold Extractor Spring.

I also would not trust that buffer spring. Does it allow proper buffer pad contact with the rear of the buffer tube? You test it by using grease on the buffer pad. Sometimes the spring coils are too fat and allow the buffer spring to go to solid height before the buffer can do it's job.

A Tubb .300 buffer spring or a Colt Action Spring is what I would be using.

Check the ejector for mushrooming of the edges. Putting a beverage on it will help reduce ejector sticking.

IMO running a .300 without adjustable gas and shooting various loads with and without a can is unreliable.

Gun needs a clamp on SLR, Gas Port Opened,

clandestine · Dec 12, 2017

GuitarmanNick said:
A few questions...
Has the gun ever run reliably?
If so, did you make any changes prior to the problem?
What do your spent cases look like?
Are they shiny or frosty looking? If the latter,... clean your chamber! A dirty chamber increases resistance when extracting spent cases.

I still suggest looking at the barrel's gas port if the chamber is clean and the extractor is good. Gas system flow being too low can cause the exact condition that you have described. This is especially true is you are not getting the bolt to hold open on the last round. Assemblers sometimes leave them loose or do not have them properly aligned and manufacturers sometimes have a defective part get through their quality control measures. Larue missed an undersized gas port on an $1100 upper even after it was sent back to them twice with complaints that it would not feed and was unreliable! The owner figured it out after 6 years of trying everything else he could think of after resigning himself to the fact that he paid way too much for the upper! He finally took a hand drill and drilled the port to a slightly larger size resulting in the gun running reliably for the first time. It will now eat any ammunition he feeds it without failures.

Routine cleaning of an AR usually does a good job of cleaning the gas port and few take the time to actually disassemble the upper and check it. It is also possible that there is a partial obstruction in the port or gas tube.

If after swapping bolts, cleaning the chamber, etc... you are still having issues, tear that sucker apart and make sure the port is clear. If the gun has never run reliably, check the port size!

You do realize that gas ports on an AR don't clog unless you shoot lead projectiles past it right?

Overgassed and undergassed AR's behave in similar fashions. Just because a gun won't cycle don't mean it's undergassed. Overgassing will also prevent extraction.

BenL · Dec 13, 2017

clandestine said:
Lots of factors here. Outrider has said all that I would have said.

I'll add that gas key bolts can be a problem. To test them you use reverse inch pound torque at 30in# if they move the bolts are undertorqued or broken which will allow has to leak.

An oversized Gas Key or a worn Gas Tube can allow wear as well.

Are you using a one piece gas ring? If so ditch it.

If it were me it would get a Tubb Ejector Spring or Brownells CS Ejector Spring, and a New Colt Extractor and Colt Gold Extractor Spring.

I also would not trust that buffer spring. Does it allow proper buffer pad contact with the rear of the buffer tube? You test it by using grease on the buffer pad. Sometimes the spring coils are too fat and allow the buffer spring to go to solid height before the buffer can do it's job.

A Tubb .300 buffer spring or a Colt Action Spring is what I would be using.

Check the ejector for mushrooming of the edges. Putting a beverage on it will help reduce ejector sticking.

IMO running a .300 without adjustable gas and shooting various loads with and without a can is unreliable.

Gun needs a clamp on SLR, Gas Port Opened,

Thanks, Chad. Great advice, as always. I like the SLR gas blocks; have on on my HM rifle and it runs great.

For clarification: is your buffer spring recommendation good for pistol gas system with pistol buffer tube? I'm using this buffer tube...

AR gas question

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