AR-10 Malfunction Advice - got some?

[rbernie]

Copy. It stands to reason, then, that a heavier spring/buffer might in fact help (mask the issue) because it will potentially reduce the bolt velocity and give the magazine more time to advance the round stack.

 

[Slamfire]

Ah, Slamfire... the loads are 155 grain Nosler Custom Competition bullets over 45.0 grains of IMR-4064, COL is 2.800" and by my chronograph, doing 2,846 FPS. Not an overly hot load, and it functions perfectly in a Rock River LAR-8. I can certainly try something a little lighter though. Thanks. (oh, that was 2,846 out of a 26" barrel, not this 16")

In my opinion, your load is too hot. Based on my experience, you don't want a load greater than 43.5 grains IMR 4064 with a 150 or 155 bullet. That may still cause malfunctions. Cut back to 42.5 grains and see if your malfunctions go away. You don't want to be near 2800 fps, be just at, or a little above, 2700 fps.

 

[cougar1717]

My guess is, I should try a heavier buffer to slow things down, but I know there's guys out there who have more knowledge than I do.

I'm not seeing a large array of buffers out there though... what's the recommendation from those who know?

RainDodger, there is good advice here, but reading your first post made me think that you first want to doublecheck your carbine buffer to make sure it is an AR-10 buffer and not an AR-15 buffer. The AR-10 carbine buffer when used with a standard buffer tube should look like this https://www.midwayusa.com/product/232006/dpms-buffer-lr-308-carbine or this http://www.primaryarms.com/anderson...-spec-stock-hardware-kit-am-21-buffer-kit-308 . They are short and stubby because it has only has two tungsten weights to account for the 308's longer bolt length when used with a standard buffer tube.
So there is not enough room to add any buffer weight without an extended buffer tube. Your first post just made me wonder if the buffer is AR-15 length (ie for an Armalite AR-10) which needs an extended tube.

Assuming the buffer and tube assembly is correct, the second thing I would do is work up a lighter load. It sounds like the bolt is moving too fast to correctly cycle. You said your reloads were not an overly hot load and I would agree if it was a bolt action......but AR-10 pattern rifles are just different. Even your LAR-308 - it may be able to handle it, but this rifle definitely does not. AR-10/LR-308's can be finicky in order to cycle correctly.
BTW, if you've shot a good amount of your reloaded ammo in this or in your LAR, be sure to check the gas key bolts on the BCG because 308's can loosen them up.

The third thing would be to install an adjustable gas block. Some people call AR-15's overgassed with 25gr powder. Remember that the AR-10's bolt, buffer, and spring assembly are heavier, but it is 40+ grains of powder on average, so it's really overgassed.

 

[Slamfire]

I think this is a good object lesson in confirmation bias. The OP thinks that 2846 fps with a 150 is " not hot, is good, because the load functions in another AR action.

Serendipity on the first go is actually bad. I remember in Eddie Rickenbacher's book "Fighting the Flying Circus" he stated how lucky he was not to have the cream before the milk. He knew flyers who got lucky, first thing, did not learn caution, assumed they would always get the cream, and these guys got themselves into situations from which they were unable to survive.

I have been testing 150gr Federal Fusions in my 30-06 bolt rifle, it has a 24" barrel and I have chronographed loads at 57.0 and 59.0 grains AA4350. Manuals variously give 57 as a max, or 59 grains as a max. I am not breaking 2800 fps with either load, and this is a 30-06!

Anyone thinking that adding weights to the bolt carrier is a substitute for cutting the load is going to find that will not work well in practice. I used Tubb weights in my AR15's, they worked well, they aided in function reliability by adding weight as the bolt carrier went forward and ensured a more positive feed and bolt closure. It was not a solution to hot loads as bolt/carrier weight is in the noise level compared to port pressure if the desired effect is to reduce bolt velocity. Also, it won't prevent primers from popping out of the pocket and jamming the mechanism. In the field, you won't like knocking out the trigger pins and removing all the trigger parts to find that primer at the bottom of the well.

Gas guns are not bolt guns, they are a lot more sensitive to pressures and if you don't have the port pressures correct you will have malfunctions. I think the OP has set himself on a quest, a quest to figure out how to stop bolt over ride problems without cutting barrel and port pressure. This quest will be a failure, but everyone is entitled to spend a lot of time and effort figuring out they were wrong.

If you want velocity more than reliable function in your gas gun, well, have fun with it.

Jams were one reason seasoned AR shooters always had a multi tool with needle nosed pliers on their belt. The ejection port in an AR is too small to reach in with your fingers and clear jammed cartridges.

My Wave has cleared lots of jams, from mine and others AR's. Word to the wise:

 

[RainDodger]

At this point, that will be my second solution if the heavier buffer doesn't take care of the problem. Thanks everyone.

 

[RainDodger]

Slamfire, I just read your post - didn't notice it earlier. I will take what you say under serious advisement. I suspect you're right and will likely install an adjustable gas block directly after trying a heavier buffer. I see the logic in fixing the problem and not just the symptom. Operating 100% AND with lower pressure seems to me to be a better option all around. Since I already have the buffer coming, I will try that initially. Only one change at a time in order to assess exactly what's happening.

As for the load... no, I'm not looking for velocity at all. I don't shoot at extreme ranges and have other rifles I would use for that endeavor anyway. I happened to settle on this load as it's extremely accurate in a different rifle. (and factory loads (Federal) are giving the same malfunctions, btw... which also points to the probably need for an adjustable gas block)

 

[HankC]

Since you reload, you can try loading ammo with lighter load to see if that is your problem before you do anything. I run 42 gr 4064 in my 308 AR. If the problem is over gassed, you should see improvement with lighter load. If over gassed and bolt cycles too fast, more likely not picking up next round but your rifle picks up next round and have bolt over which is more like cartridge not released soon enough while bullet tip is rising and cause the base dive under. Feed ramp issue? How does it cycle and feed by hand in slow motion?

 

[M1key]

Lyman's 308 accuracy load and starting load is 47.0 grains behind 150gr bullets work very well and approximate NATO pressures I believe.

good luck

M

 

[Slamfire]

Lyman's 308 accuracy load and starting load is 47.0 grains behind 150gr bullets work very well and approximate NATO pressures I believe.

good luck

M

That would be an appropriate load for the 30-06, not the 308 Win.

 

[M1key]

Modern Reloading Edition 2
.308 150 Grain Jacketed Bullet--H380--47.0 Start Grains---51.0c Max Load

Lyman Reloading Handbook 47th edition
308 150 Jacketed SP
H380 47.0 2695 42,900 53.0 2949 51,200
(actually underpressure here)

The load cycles fine, clean ejection in the FALs without changing any gas settings from original NATO ball (RG, R1M1, ADI) and even works in the Saiga.


M

 

[MistWolf]

The bolt will not push the round out of the magazine unless the bolt catches the rim. If the bolt catches the rim, it will feed the round into the chamber. The only way to get a bolt over ride is if something stops the round from feeding into the chamber. That something is usually the empty case due to a weak extractor spring. Normally, the empty gets caught in the action, but sometimes, it makes its way out after blocking the new round from feeding.

I know many think it's excessive carrier speeds out running the magazine. I have experimented with a grossly over gassed upper and for all its faults, I could not get it to out run the magazine.

Excessive carrier speeds will stress a spring that's starting to fail and slowing it down will eliminate extraction issues. For a time. But they will come back if not fixed.

RainDodger, the heart of your problem is the extractor spring and possibly the action spring. If you don't address them, you'll end up chasing your tail as you attempt to solve the over gassing issue, if indeed your rifle is over gassed.

 

[Slamfire]

Modern Reloading Edition 2
.308 150 Grain Jacketed Bullet--H380--47.0 Start Grains---51.0c Max Load

Lyman Reloading Handbook 47th edition
308 150 Jacketed SP
H380 47.0 2695 42,900 53.0 2949 51,200
(actually underpressure here)

The load cycles fine, clean ejection in the FALs without changing any gas settings from original NATO ball (RG, R1M1, ADI) and even works in the Saiga.


M

I missed the powder change, I thought the discussion was about IMR4064.

 

[Cornpimp]

Just an observation from a guy that has built a lot of AR10's. If it's not picking up the next round properly, how can it be "over gassed"? Gas is what starts the "action", or the removal of the spent round. Picking up a new round from the mag is the job of the BCG and the buffer spring, the reaction. The bolt isn't going back far enough to get the new round out of the magazine. Is your empty clearing the action completely?

 

[Nature Boy]

I missed the powder change, I thought the discussion was about IMR4064.

I think we still are. M1key seems to be throwing out his favorite load for .308 using H380.

I'm with you Slamfire. I think the OPs load is too hot. Only 0.5g from Hodgdon max.

@RainDodger, before you go rearranging your rifle, why not try backing off on your powder charge? Why beat the heck out of a gas operated semi-auto pushing a 150g bullet over 2,800fps if it's not necessary and potentially the cause of feeding problems? You can find an accuracy node a lot lower down the power curve.

 

[Powder296]

Sounds like a possible magazine problem as it had started to strip the next round but failed to come completely out of the magazine and the bolt is hitting halfway up the cartridge if I'm understanding correctly. I would try a different magazine and ensure the magazines are completely seated on an open bolt and then let the BCG go without holding it back and see if you have any issues.

I had an AR15 do this exact thing, turned out the problem was the upper had no feed ramp cut into. The tip of the bullet was hitting the breach face and the bolt rode over it enough to jam the rifle and make the jamed case unusable. I had a local smith that knew just how much to grind cut feed ramps into it. Problem was fixed for about $60 if I remember correctly. That was some years ago when feed ramps were still largely optional, needless to say it was my first and last rampless upper,

 

[Powder296]

I also have an LR-308 factory carbine. In order to soften the recoil a bit I swapped some parts with stuff I already had in stock because of a couple builds I was doing at the time. I changed the factory carbine buffer and tube to the Vltor A5. The tube is an exact fit, but given the extra length I am able to use a heavier buffer. I put the Vltor H4 buffer in it(6.83oz), and a standard rifle spring. I've only got about 150 rounds through this setup but it's been flawless, and it shoots a bit softer than the ridiculously small factory buffer.

If I ever find the need/desire to change the barrel on this rifle it will get a longer gas system and an adjustable gas block

 

[RainDodger]

Just a couple of quick notes... yep, I will try a lower power load asap. Easy to do. Those thoughts make sense. Regarding the feed ramps - they look fine to me - just a larger version of M4 feed ramps. When the jam happens, the bullet tip is not pressed into the ramp. The bolt is pressing against the side of the case, which is also causing a lot of deformation of the case shoulder against the chamber opening on the underside of the case (logically). Update: I have ordered an adjustable gas block just for grins. Also on the list is the potential spring issues, per MistWolf.

Lots of good thoughts here, and I thank you all. I will put together some softer loads before the next range trip.

 

[d'zaster]

I'd suggest a heavier buffer

 

[rbernie]

The bolt will not push the round out of the magazine unless the bolt catches the rim.

This is correct. However, I do not believe that is the symptom been described.

In a bolt-over-base jam, the round remains below the level of the bolt face. When returning to battery, the bolt then jams into the top side of the case rather than striking the rim and pushing it forward. The round may push further forward, and the nose of the round may jam into a feed ramp, but the key symtom is that the bolt did not strike the rim but made contact past the rim up the case body

 

[MistWolf]

1) The bolt cannot push the case out of the magazine by striking the case body. There isn't enough traction.

2) Raindodger says the rifle always locks back on the last round. The bolt is traveling rearward enough that it will catch the rim.

3) If carrier speed were so fast that it was outrunning the magazine, Raindodger would also be asking how to soften the recoil because it would be sharp and painful.

4) If carrier return speed was too slow to feed the round completely, the bolt would not be overriding the base.

Taking all of the facts into account, it points to a weak extractor spring. If not the extractor, then it's the ejector spring. Or both.

 

[someguy2800]

1) The bolt cannot push the case out of the magazine by striking the case body. There isn't enough traction.

2) Raindodger says the rifle always locks back on the last round. The bolt is traveling rearward enough that it will catch the rim.

3) If carrier speed were so fast that it was outrunning the magazine, Raindodger would also be asking how to soften the recoil because it would be sharp and painful.

4) If carrier return speed was too slow to feed the round completely, the bolt would not be overriding the base.

Taking all of the facts into account, it points to a weak extractor spring. If not the extractor, then it's the ejector spring. Or both.

I'm not sure I understand, can you elaborate on why the ejector or extractor is causing it to loose control of the round and miss feed? I assume you mean the spent case is not properly clearing the action and is fouling the next round as its feeding out of the magazine? Awhile back my AR15 was overriding and jamming the bolt into the side of the case with the tip of the bullet jammed up in the barrel extension. Just want to better understand what may have been causing that.

 

[MistWolf]

I assume you mean the spent case is not properly clearing the action and is fouling the next round as its feeding out of the magazine?

Yes.

The AR ejector is a plunger type. To work, the case must be held fast against the bolt face until the case mouth clears the ejection port. When the extractor loses control of the extracted case before it can be ejected, the ejector cannot push it out. The case stays in the action and impedes feeding of the next round. Usually, the empty is caught in the action along with the round partially stripped from the magazine. Sometimes however, the case gets knocked out of the ejection port leaving the shooter with just the bolt over.

Both types of malfunctions are all to often misdiagnosed. When the malfunction is an empty case and a bolt over, people will call it a "Double Feed". It is not a "Double Feed". A double feed is when the magazine releases two rounds into the action. A double feed is strictly a magazine problem and the only fix is to replace the magazine.

When the malfunction is just a "Bolt Over", it is still the result of the empty case fouling the feeding of the new round. The difference is, for whatever reason, the empty made it's way out of the action after causing the malfunction. It's often misdiagnosed as excessive carrier speeds outrunning the magazine. If the AR were full auto, it may be possible as the continuous cycling of the action can create dynamics not present in semiauto fire. But in semiauto fire, in order for the carrier to outrun the magazine, it would have to run extremely fast (which would make itself known through sharp and painful recoil) or due to a junk magazine.

Whenever there is a bolt over, it's usually due to the extractor losing control of the empty. In a few cases, it could be due to weak ejection, but weak ejection usually manifests itself as stovepiping.

Bolt overs can be induced by over gassing, but only if the extractor spring is weak or starting to lose it's temper. Over gassing will not cause bolt overs if extraction and ejection are good.

 

[someguy2800]

Yes.

The AR ejector is a plunger type. To work, the case must be held fast against the bolt face until the case mouth clears the ejection port. When the extractor loses control of the extracted case before it can be ejected, the ejector cannot push it out. The case stays in the action and impedes feeding of the next round. Usually, the empty is caught in the action along with the round partially stripped from the magazine. Sometimes however, the case gets knocked out of the ejection port leaving the shooter with just the bolt over.

Both types of malfunctions are all to often misdiagnosed. When the malfunction is an empty case and a bolt over, people will call it a "Double Feed". It is not a "Double Feed". A double feed is when the magazine releases two rounds into the action. A double feed is strictly a magazine problem and the only fix is to replace the magazine.

When the malfunction is just a "Bolt Over", it is still the result of the empty case fouling the feeding of the new round. The difference is, for whatever reason, the empty made it's way out of the action after causing the malfunction. It's often misdiagnosed as excessive carrier speeds outrunning the magazine. If the AR were full auto, it may be possible as the continuous cycling of the action can create dynamics not present in semiauto fire. But in semiauto fire, in order for the carrier to outrun the magazine, it would have to run extremely fast (which would make itself known through sharp and painful recoil) or due to a junk magazine.

Whenever there is a bolt over, it's usually due to the extractor losing control of the empty. In a few cases, it could be due to weak ejection, but weak ejection usually manifests itself as stovepiping.

Bolt overs can be induced by over gassing, but only if the extractor spring is weak or starting to lose it's temper. Over gassing will not cause bolt overs if extraction and ejection are good.

Thanks. I don't believe this description can be applied to what I was experiencing. In my case the spent case would be thrown the normal distance of mabey 6 or 8 feet when the over ride would occur and I don't recall ever having a spent case stay in the action or fall at my feet. Mine was probably different than the OP's since mine was also not locking back. A lighter buffer and spring fixed mine and its never done it again.

 

[RainDodger]

In my case, ejections appear to be totally normal, with the ejected case being thrown with "normal" force in an expected direction. Thanks for your description of a spring-related malfunction. It's on the list of things to check to solve the issue. I wish I could run outside and check each one of these potential problems, but I have to wait for parts to arrive via our sterling mail service! Then install, then test, and the range isn't in my backyard! (wish it was!). As I said earlier, I'll let this thread know what I test and what the results are!

 

[RainDodger]

First update! And an interesting one!

As it happens, a friend and I built two identical rifles. He has been out of town and unavailable to test his rifle. Every single part between the two rifles is identical. He returned from his trip recently and was finally able to test his rifle today. As is totally logical, his malfunctions were absolutely identical to mine. He was testing with factory Federal 7.62 rounds and not hand loads.

He ordered the heavy buffers, not me, so he had them with him at the range. He popped in one of them to see if it would magically make things perfect. SAME malfunction. No change. So the heavy buffer has made no difference!

Next up is the adjustable gas block. I have installed mine and we'll install his on Thursday when we test both rifles. The gas blocks are new, made by Odin and they appear to be really nicely made. The adjustment is via allen screw which is typical, but there are 26 separate detents available for a tactile feel when moving the screw. A welcome improvement in my view. No need to use any loctite on the adjustment screw, and easy to alter the setting anytime. I will let this thread know of the results on Thursday!

Roger