Calling all AR experts (particularly AR10)...

[Danoobie]

Does the rifle have a muzzle break? Some designers are much more worried about how tacticool your rifle
looks, at the LGS, than how it shoots, once it's sold. I just went thru the whole AR10 "burn your way thru 20
boxes of ammo, why, oh why doesn't it cycle right ?" just to realize that the muzzle break those short-strokers
back at the factory cranked onto the barrel with a 60 inch pipe wrench was causing the world-class stove pipes,
which, BTW, they might have caught, on their own range, (if they have one) IF they had bothered to test their own
prototype. The proper tension mag springs? Who needs them? As long as the gun looks cool, on a store wall
somewhere, who cares?

I would assume nothing, eliminate every tacticool POS on the rifle you find,(a dead giveaway that it's useless is
how hard it is to remove from the rifle body) and remember that the manufacturers ambivalently sent your rifle out for
sale, having NO IDEA how it would perform in the field, the way they set it up.

WELCOME to the wild world of AR10 designers who don't have the sense it takes to crap in the direction of gravity.

 

[bfoosh006]

There is no evidence the problem is over gassing.

Typically , .308 Ar's are "over gassed" the shear volume of gas from the .308 cartridge is best handled by an adjustable gas block.... add to that a relatively light buffer and a ok'ish recoil spring and cyclic problems are amplified.

Do you have an suggestion on how to address the issue ? ... I am not trying to be flippant.. I am just curious as to other ideas.

 

[MistWolf]

The rifle may or may not be over gassed. I don't know because I have no hands on experience with this model. But there is no eveidence the problem is being caused by an over gassed condition.

I strongly believe the problem is due to the extractor losing control of the case rim. That is normally caused by a weak extractor spring but may also be due to an out of spec extractor. My next guess would be the ejector, but my money is on it being an extraction issue as I stated in my earlier post.

Now, it may be the extractor spring has not failed entirely. It may have weakened just enough that with the rifle being over gassed, the extractor cannot handle the extra stress. It may be that reducing gas flow with an adjustable gas block will let the spring start doing it's job once more. But it won't fix the problem. The spring will continue to weaken with use and the problem will return.

If the rifle is over gassed, it will do no good to install an adjustable gas block and attempt to tune it without fixing the extraction issue. I can tell you from personal experience that attempting to tune an AR with extraction issues won't work.

 

[Danoobie]

If the company has a better rep for customer service than quality control, perhaps you could send it
back, if it is still under warranty. I would have done it with mine, if the warranty had been in force.

 

[Hummer70]

What you have pictured in your first thread is a "bolt over base" malfunction". This problem is well known at Aberdeen Proving Ground. Most AR malfunctions are this failure and the majority of them occur from full magazines in the 1st or 2nd round. Some mags are more prone to this stoppage.

We numbered magazines and when BOB occur we noted the round number in the stack that BOBed and the mag number. The same mag was rotated through all weapons in test cycle. If mag had BOBs in other rifles it was charged to mag. If only one rifle stopppage was charged to rifle.

BOBs occur sometimes down to the third round. This is why troops in Nam were told to load 18 rounds in 20 rd mags and 26 rounds in 30 round mags which is what I do for home defense applications.

As I understand it now the M855A2 rounds with all steel cores are engraving the feed ramp until a ridge appears at the end of the gouge trough and then the meplat stops cold right there. Only thing to do is replace barrel. I understand there is a new mag variation in the works that changes the feed angle of the round in the magazine as top rounds are fed forward.

If your mags are new depress the followers and wipe the inside of the mag with lubricant. Also check round lengths for over length rounds.

 

[MachIVshooter]

The rifle may or may not be over gassed. I don't know because I have no hands on experience with this model. But there is no eveidence the problem is being caused by an over gassed condition.

I strongly believe the problem is due to the extractor losing control of the case rim. That is normally caused by a weak extractor spring but may also be due to an out of spec extractor. My next guess would be the ejector, but my money is on it being an extraction issue as I stated in my earlier post.

Now, it may be the extractor spring has not failed entirely. It may have weakened just enough that with the rifle being over gassed, the extractor cannot handle the extra stress. It may be that reducing gas flow with an adjustable gas block will let the spring start doing it's job once more. But it won't fix the problem. The spring will continue to weaken with use and the problem will return.

If the rifle is over gassed, it will do no good to install an adjustable gas block and attempt to tune it without fixing the extraction issue. I can tell you from personal experience that attempting to tune an AR with extraction issues won't work.

OP did not mention extraction problems at all.

That said, when mine were way overgassed running suppressed, they did suffer extraction problems. The bolt was running so fast that not only did it outrun the magazine, the empties couldn't get out of there in time either. I had the same type of jam the OP described, plus an empty lodged above it. Tuning the gas fixed it.

Sometime I'll open up the valve and make a video of that happening.

 

[MistWolf]

OP did not mention extraction problems at all.

This statement

Three rounds loaded single in magazine, two different ammos (federal 223 and Winchester 7.62), bolt locked back each and every time on empty mag.

combined with this photo

tells me the problem is likely to be the extractor. While the empty case did make it out of the ejection port, it was inside long enough to interfere with the feeding of the next round and that could only happen if the extractor lost control of the extracted case.

That said, when mine were way overgassed running suppressed, they did suffer extraction problems. The bolt was running so fast that not only did it outrun the magazine, the empties couldn't get out of there in time either. I had the same type of jam the OP described, plus an empty lodged above it. Tuning the gas fixed it.

Sometime I'll open up the valve and make a video of that happening.

I had the very same problem when I built and suppressed an AR pistol. When I tuned down the gas using an adjustable gas block, it ran and ejected fine. Until a couple hundred shot later when the same problem returned. It was because the extractor spring was failing. I have had this happen more than once and the solution every time has been to replace the extractor spring with the Colt M4 extractor spring.

When I did the first test fire of the AR pistol, the gas port was huge. Carrier speeds were so fast, it hit the hammer hard enough to send a sharp sting through the trigger and it hurt. But the carrier did not outrun the magazine which was a fully loaded thirty round MagPul. I don't think the problem here is the carrier out running the mag. You gotta have really fast carrier speeds at full auto to do that. Or a really weak mag spring.

High carrier speeds won't cause the extractor to jump the rim unless there is a problem with the extractor or the extractor spring. An extractor and spring that is in good shape will tear the rim of the case before it lets go of it before ejection.

 

[berettaprofessor]

For those who have suggested returning the rifle; remember this is a build; many parts are Stag, but it is not all Stag and they didn't assemble the rifle. I wouldn't expect them to fix it.

There seem to be two camps of consensus; Those who think the rifle is overgassed and those who think the extractor is weak or failing. Since I don't know, can someone tell me how to test the extractor? It's a new spring and I inspected it when I had the extractor removed and bolt disassembled to check headspace. I've cycled the rifle with unfired cartridges and it chambers and extracts as expected at hand speeds. I can't move the extractor with just hand/finger pressure, so I'd say it's pretty tight. But how do I really find out?

 

[ColoradoMinuteMan]

For those who have suggested returning the rifle; remember this is a build; many parts are Stag, but it is not all Stag and they didn't assemble the rifle. I wouldn't expect them to fix it.

There seem to be two camps of consensus; Those who think the rifle is overgassed and those who think the extractor is weak or failing. Since I don't know, can someone tell me how to test the extractor? It's a new spring and I inspected it when I had the extractor removed and bolt disassembled to check headspace. I've cycled the rifle with unfired cartridges and it chambers and extracts as expected at hand speeds. I can't move the extractor with just hand/finger pressure, so I'd say it's pretty tight. But how do I really find out?

I don't know that there is a definitive test. My feeling is if you are getting an extraction every time I would prioritize the timing of the gas system over the extractor. You can always come back to that. In the meantime you could always just buy another spring so you have it. If you fire enough rounds you'll want to replace it at some point down the line and they are cheap, common replacement parts to have on hand. I'd focus on slowing down the cycle time. Buffer spring, buffer mass, and (or) gas volume are going to be the factors to play with at this point. I'd take them on 1 by 1 and introduce only one change st a time. Your gas system length and gas port are fixed variables without replacing the barrel and there is no need for that with the knowledge we have at this point.

 

[MistWolf]

Your test has already been performed. The extractor sometimes loses control of the empty case before it can be ejected. The rifle passes the lock back check. It all points to the extractor.

If it's not the extractor, it's the ejector.

 

[ColoradoMinuteMan]

Your test has already been performed. The extractor sometimes loses control of the empty case before it can be ejected. The rifle passes the lock back check. It all points to the extractor.

If it's not the extractor, it's the ejector.

I believe the picture you are seeing and the quote are from two separate series of testing. I guess I'm just missing the clear indicator that the extractor is losing control of the spent cartridge. It extracts each and every time. I'm by no means saying it's impossible, I'm just saying I'm having a hard time understanding how it's it and dry. I see symptoms that are often manifested from gas system / impulse timing issues. It seems natural to explore that.

 

[MistWolf]

Tell you what- Find out what extractor spring your Stag bolt uses. If it uses a M4 type spring, I'll send you a brand new Colt M4 extractor spring in the mail. Try it & see if it doesn't fix your problem. All I ask is that you make sure the extractor isn't worn or bent (if it is, replace it) and that the ejector also works. Do a flick test. That's where you pull the BCG from the rifle, put an empty in the bolt and press it against the ejector with a finger. Flick the finger away and see how far the ejector throws the empty. It should go pretty far.

Do that and PM your addy and I'll send you a spring. Free. I'm betting it will fix your bolt over problem.

 

[berettaprofessor]

Brief update; received the adjustable gas block and placed it on last night. Now the darned thing won't lock the bolt back at all, nor even start to extract the case, so I've concluded my port alignment is off. Realigning today and will try again.

MistWolf, I appreciate the offer and I'll keep the extractor spring possibility in mind, but pursuing other things first. I just have a hard time believing that the extractor is losing control of the case when every case lands within a one foot diameter circle to my back and left about 3-4 feet out. I also have no idea what extractor spring is there and I'll have to get CS at Stag to tell me which will take awhile. If I can't get the adjustable block to work, I'll put the first one back on, confirm bolt lock-back again, and then move on to trying heavier buffer and changing extractor spring.

 

[M1key]

edit

 

[ColoradoMinuteMan]

Brief update; received the adjustable gas block and placed it on last night. Now the darned thing won't lock the bolt back at all, nor even start to extract the case, so I've concluded my port alignment is off. Realigning today and will try again...

...If I can't get the adjustable block to work, I'll put the first one back on, confirm bolt lock-back again, and then move on to trying heavier buffer and changing extractor spring.

I'm curious your positioning of the gas blocks. I haven't paid attention to your barrel profile, but assuming there is a shoulder where the bas block profiling meets the barrel profiling aft of the gas block, is the gas block butted up against the barrel shoulder, or is it spaced off the shoulder to compensate for the thickness of the non-existent hand guard cap? Though many gas blocks have enough tolerance that this isn't an issue, I like to place my gas blocks .025" away from the barrel shoulder to compensate for where the hand guard cap would be, thus helping center the gas ports and assuring full flow of gas.

Also, not at all trying to insult anyone's intelligence, but sometimes it's the small easy things that get missed, are you sure the gas block adjustment was opened up all the way when you tested it?

 

[berettaprofessor]

ColoradoMinuteMan, you can't insult my intelligence when I'm in new territory because I'm absolutely sure that I don't know what I don't know! I am sure, however, it was opened up completely, which I tested by opening it the prescribed amount while I could see the gas port and see that the prescribed "4.5 CCW" turns really did open it completely. And I opened and closed it it more than once while testing, making sure I had that part right. I did place the block 0.025" away from the shoulder with a feeler gauge, but it is such a small port that I probably had it rotated just slightly off midline.

Anyway, after readjustment, it did cycle and extract, and the bolt locked back on the first shot. After that, no matter the adjustment and even after opening it full again, it wasn't locking the bolt back. Maybe the newly oiled bolt on the first shot? I've now placed the original unadjustable gas block back on which has a much larger port and more room for placement error. Will test tomorrow, and if it's again locking the bolt back consistently, then I'll try different ammo, different mags, and order new extractor spring per MistWolf and the heavier buffer you recommended. I'm so close.....

 

[ColoradoMinuteMan]

Best of luck, I hope it all just works. Maybe you should hit MistWolf up on that extractor spring.

 

[berettaprofessor]

Well, with the non-adjustable gas block, the bolt consistently locks back again but it still has the original feeding problem; most of the time. I filled a magazine as suggested to compress the spring more and got 2 normal feeds until it FTF'ed again (on the 3rd shot). I guess that's progress and it makes me more suspicious of the new mags. I've ordered a different brand, metal, AR10 mag, new extractor spring, wolff extra power extractor spring, and the Tubb flat buffer spring recommended by bfoosh. If those don't work, that $55 heavy buffer is in my sights...so to speak.

In the meantime, I'm still pretty enthused about the rifle itself. Stag's machining is very tight and if anyone is looking for a really light and nice MLOK handguard, this one is fabulous.

 

[MachIVshooter]

Someone put your ejection port and FA on the wrong side..............

 

[berettaprofessor]

A lot of my things are on the wrong side.

 

[bfoosh006]

Is the chamber clean ?... If not, clean it. It will help with any possibility of stickiness during extraction

And while your extractor "might" be faulty... I still believe the cyclic speed is to fast... the speed is overwhelming the time needed to eject the spent case.

I have forgotten by now... what specific brand Mag ?


IMHO, after you get the heavier buffer and Tubbs recoil spring ... I would re-install the adjustable gas block and re-adjust it. You should see a dramatic difference in recoil.

I am slightly concerned that you might have a AR15 carbine spring, rather then a .308 carbine spring.

I just completed my break in on my 6.5CM PSA upper and after using the recommended stuff here it runs like a champ.

If you weren't so far away... I'd be more then happy to help tune your rifle.