Need help - AR10 cycle problem

[sled_mack]

Rifle specs first:
.308 Win
Armalite AR10A4
20 inch SS barrel
Replaced original handguards with Troy 2 piece free-float
Replaced original stock with Magpul PRS
Replaced original buffer with "Slash" heavy buffer. (I went to the heavy buffer when I tried shooting FGMM 168 grain and it nearly ripped the rim off the case.)
Stock gas block, non-adjustable or switching.

All modifications to the gun were made last summer. Gun ran fine for a year.

I think that covers everything. If I missed something relevant, just ask.

The symptom while shooting is failure to eject. It appears the the rifle is short stroking. The empty case is extracted from the chamber but not ejected from the rifle. Ejected cases land at about the 3 o'clock position from the gun.

At first I thought it was just dirty or not enough lube. Cleaning and adding lube did not help. But, what I noticed is that the bolt does not move smooth in the carrier. As the bolt is moving out of the carrier (same motion as if extracting a round from the chamber) the bolt "hangs up" just before the gas rings get to the exhaust ports on the carrier. Even if I remove the cam pin so that I only have the resistance of the gas rings in the carrier, the bolt gets hung up at the same point.

I thought maybe the gas rings were the problem. I ordered a new set from Armalite. Installed them and thought I had the problem solved. On the bench, the bolt moved freely in the carrier. However, 15 rounds in the first range trip and I had a fail to eject. Emptied the gun and worked the bolt, and could tell it was getting hung at that same spot again. Took it apart, and sure enough, the bolt was hanging at that same point.

I can't see any signs of damage in the bolt carrier where the gas rings are touching. The gas rings move free in the ring on the tail of the bolt.

I talked to Armalite today, and the conversation came to a bit of a halt when I mentioned a heavy buffer. Their suggest is to try it with the original and see what happens. I asked about the bolt not moving free in the carrier, but he didn't really want to talk about that.

I can try the original buffer easy enough. But I can't help but think that if there IS a problem with the bolt or carrier, the light buffer is only going to mask it over until the failure gets worse. On one hand, at least when it totally fails I'll know what the problem was. But we all know that will happen during the middle of a match or class.

Thanks in advance for any ideas or suggestions.

 

[0V3RC10CK3D]

Re: Need help - AR10 cycle problem

If it's not cycling all the way it very likely could be the heavy buffer. Sounds like the buffer is slowing down the bolt too much and it's losing it's momentum to fling the casing hard enough out of there so it gets stuck when the bolt is on the way back forward.

It could also be a gas problem. Try pulling the bolt carrier group out of the gun, pull the bolt to the forward position and set it face down on the table, it should be able to hold it's own weight without collapsing on itself. If not there's probably a gap somewhere between the bolt and bolt carrier where gas is escaping instead of pushing the bolt carrier back with it.

It definitely could be the buffer though. Lube everything up super well. Ar's like to be dripping wet with lube.

 

[sled_mack]

Re: Need help - AR10 cycle problem

I will try the buffer. But I'm still afraid it will just mask over a problem that does exist.

I did try that test of setting the BCG on the bolt face. With the new gas rings, it did not hold it's weight up. It collapsed right away. After shooting it, it collapses to the point where it "hangs up" when pulling the bolt out, and then it supports the weight of the carrier.


Another thing to note - After cleaning and lubing the BCG it operates smoothly in the gun. After 30 or 40 rounds the bolt is stiff to get open on an empty chamber. Once the bolt is unlocked, the carrier moves free.


Just got a call back from Armalite's repair shop. Very helpful gentleman. He's going to send me a new ejector spring and extractor springs. He also pointed out that my rifle is old enough to be "gen 1" and they have a package to upgrade to "gen 2" for $150. I might give that a try over the winter. We're getting to the last few weeks of the shooting/match season and I hate to be without it now.

 

[VKC]

Re: Need help - AR10 cycle problem

I had something similar happen to my AR10, and suspect that the problem is in your bolt engagement area.

Check the bolt for burrs or imperfections that may be causing this, and smooth out if so.

Spray some Wipe-Out or similar foaming cleaner into the barrel chamber and bolt engagement area and let it set for a while. Then take a cloth chamber mop soak it Butch's or similar solvent and power scrub the chamber.

 

[Sc0]

Re: Need help - AR10 cycle problem

Did you re-center the gas block after installing the handguard?

Try the OEM buffer, if it works the same by almost ripping off the heads of the cases then the gas port is fine, if not then it is a place that needs attention.

Does the Cam pin have any burrs on it?

 

[sinister]

Re: Need help - AR10 cycle problem

Considering the rifle functioned before the mods, my first suspicion is the placement and alignment of your gas block with the gas port hole (pretty critical), otherwise it sounds as if you might have a burr on one or more of the carrier gas relief holes (which may have been chromed-over on the inside). Hard to say since the gas ring is doing what it's supposed to.

Your mods are pretty common and straight-forward (if assembled correctly), and I almost automatically throw out the stock buffer for Slash's.

The buffer doesn't have much to do with the bolt not cycling smoothly through its unlocked and locked positions -- it should be smooth and without hang-ups.

What lube are you using that it gets blown off, dried, or coked in just a few magazines? You are lubing the bolt and all contact surfaces, correct? What ammunition are you using?

Personally I'd send it to Armalite or a good AR smith if I couldn't diagnose and correct it myself.

 

[recce556]

Re: Need help - AR10 cycle problem

Just curious but before you did the mods, you were shooting the same ammo that you are now?

Since you have the Troy 2-piece rail, I assume you didn't have to remove the gas block?

Is your PRS the one the goes over the OEM receiver extension or did you install a AR15 A1 receiver extension? If the latter is the case, are you using the shortened spring from Slash?

Also, I don't think the bolt holding the weight of the carrier test applies to AR10/308 AR's. That's a AR15 only test as far as I know.

You've probably already tried this but have you run your finger across the area inside the bolt carrier where the bolt is hanging up? Is it smooth or do you feel a burr?

Also, look at the rings very carefully, do you see any sort of mild "fold over" of the rings? IOW, are the edges sharp and vertical? I had a LMT (granted, a 5.56) bolt that would eat gas rings. Eventually, it would cause the whole system to lock up. Funny thing is, I sent it to LMT and they claimed that the carrier wasn't theirs but they replace it anyways. I bought it from a dealer that I personally know and I watched him cut open the LMT box it came in...

 

[sled_mack]

Re: Need help - AR10 cycle problem

I did not remove or loosen the gas block to put the handguards on. I did mark their location with a sharpie in case I would have to move them, and at this point the gas blocks have still not moved.

When I did the mods, I was using a 178 Amax. I changed to a 168 SMK, LC brass, and 45.5 grains of Varget. The rifle ran the first 300 of the 168 SMK loads with no problem. Now I can't get 20 or 30 without a failure.

The PRS stock is the one that goes on the stock AR10 buffer tube.

I'm using the Slip 2000 EWL lube.

I can't feel a burr inside the bolt carrier. But it's hard to get a finger in there real well.

There are no burrs on the cam pin or in the carrier where the cam pin rides. It is showing a lot of wear.

I'm going to try a few rounds tomorrow with the original buffer. I'll see if it helps. My thought is that if it works, it going to work because being overgassed will allow the gas to overcome the friction in the bolt/carrier.

The gas rings from Armalite are the one piece spiral type. I didn't see any deformation on the set I took out. I'll check the new ones after shooting it tomorrow.

Agreed, if I don't get this soon, it's going to Armalite for the gen 2 upgrade.

 

[sinister]

Re: Need help - AR10 cycle problem

Ummmmm...

back down the Varget to 44 (especially in a Lake City case) and maybe try commercial brass. Put the heavy buffer back in.

I don't think the gas port hole is affecting your cycling -- with 45.5 grains in a Lake City your cases may still be obturated against the chamber walls. While it's below Hodgdon's max of 46.0 (compressed) you're trying to work a gas-operated action.

With your 45.5 charge I'd check my rims after firing and see if the extractor's not trying to peel them off.

I don't have experience with the Slip, but keep the bolt (in the carrier) wet. You might try a petroleum oil (but I don't know if it'll matter. CLP is pretty much useless).

 

[recce556]

Re: Need help - AR10 cycle problem

Sled - it looks like you've pretty much run the gamut of examinations. At this point, sending it back to Armalite for the Gen 2 updates seems like the best bet. I was thinking about the possibly of a burr then but I remembered that you said you had shot it before problem free so if there was a burr, it wasn't hurting anything and most likely, with some round, it would have already been peened down.

Interestingly, when I had problems with my AR10 (Gen 1 like yours), Armalite had to do high speed photography testing to figure out what was wrong with it. Then ended up just giving me a new one if that tells you anything. I think the Gen 1's were more of a beta test than a finished product. My current AR10 (that I built) runs flawlessly. It has the newer forward assist upper and matching BCG...and those are the only two Armalite parts on the gun (oh, and the mag catch and bolt catch). Everything else on my current AR10 isn't from Armalite.

Sinister - I use Slip when I have it and it's an amazing lubricant. I mean it's not the second coming or anything, but it is very, very slippery and tends to keep everything going. I use it in my training carbines (5.56's) and I only need to add just a little to keep the stick running all day long (we're talking about 1K rounds in a day). It definitely should not be blowing out when only shooting double digit round counts.

 

[sinister]

Re: Need help - AR10 cycle problem

recce556, that's what I thought with the Slip as well. i have a few gift and sample bottles of the stuff but being old school ("Dinosaur") I have a quart of LSA I've been using in anything semiautomatic for years.

 

[problemchild]

Re: Need help - AR10 cycle problem

Look and see if there are any brass marks inside the oval of the ejection port area up above the front take-down pin. If you see brass marks in the front of the ejection port then you are over-gassed and the brass is bouncing forward after the bolt hits dead stop back. The brass would then ricochet around inside the port trying to get out but cant. This ricochet/failure would not happen every time only randomly.

If you see the marks you will need to install an adjustable gas block and tune the rifle. I would choose this option over a magic pixie dust heavy buffer any day as it "SOLVES" the problem instead of "MASKING" the problem.

 

[DavidAR10]

Re: Need help - AR10 cycle problem

ARMALITE TECH NOTE #80 Pg.5 line item 3:

3. If your firearm originally had two-piece handguards, dispose of the original handguard cap
and install the gas block spacer in its place.

The picture at the bottom of Pg. 4 shows the gas block spacer/ring just below the gas journal. Yeah, that's right, it's a washer that keeps keeps the gap that the A2 handguard cap occupied.

Full Tech Note:

http://www.armalite.com/images/Tech%20No...%20_Final_2.pdf

Your rifle is starved of gas.

AND, it's sound like you have nice and tight gas rings on your bolt.

 

[recce556]

Re: Need help - AR10 cycle problem

David, <span style="font-weight: bold">that isn't the issue</span>. The ONLY reason why you change the handguard cap for the spacer is because the <span style="font-weight: bold">Aramalite</span> free float handguard can not be installed with the handguard cap in place (due to the length of the handguard tube).

The SPACER is strictly there so that the gas block will seat in the same place as with the handguard cap. The SPACER and the CAP are both the same thickness and allows the gas block to return to the same offset off the shoulder.

Also, if you read the thread more carefully, you'll see that he never removed the handguard cap because the Troy 2-piece is a drop in and doesn't require the gas block to be removed.

The only way you'd be undergassing the system is if you make the common newb mistake pushing the gas block up against the shoulder rather than offsetting it. With or without the spacer, if the gas block was manufactured to be offset, it must be offset or you'll be partially blocking the gas port. That said, there are aftermarket gas block that are supposed to be pushed up against the gas block (no offset) because the gas port hole in the gas block has be relocated with that in mind.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DavidAR10</div><div class="ubbcode-body">ARMALITE TECH NOTE #80 Pg.5 line item 3:

3. If your firearm originally had two-piece handguards, dispose of the original handguard cap
and install the gas block spacer in its place.

The picture at the bottom of Pg. 4 shows the gas block spacer/ring just below the gas journal. Yeah, that's right, it's a washer that keeps keeps the gap that the A2 handguard cap occupied.

Full Tech Note:

http://www.armalite.com/images/Tech%20No...%20_Final_2.pdf

Your rifle is starved of gas.

AND, it's sound like you have nice and tight gas rings on your bolt. </div></div>

 

[DavidAR10]

Re: Need help - AR10 cycle problem

English and paying Attention to Details are hard for me.

Sorry, OP. I really thought I had it nailed for you.

I went with the ARMALITE FFHG:

I understand ARMALITE AR-10s. Have gone through @ dozen since 1999 and have three
at this time. Only Troy stuff I'm familiar with is the flips, which are on all of my
15s. The 10s have Troy rear flips with GG&G front flips.


<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: recce556</div><div class="ubbcode-body">David, <span style="font-weight: bold">that isn't the issue</span>. The ONLY reason why you change the handguard cap for the spacer is because the <span style="font-weight: bold">Aramalite</span> free float handguard can not be installed with the handguard cap in place (due to the length of the handguard tube).

The SPACER is strictly there so that the gas block will seat in the same place as with the handguard cap. The SPACER and the CAP are both the same thickness and allows the gas block to return to the same offset off the shoulder.

Also, if you read the thread more carefully, you'll see that he never removed the handguard cap because the Troy 2-piece is a drop in and doesn't require the gas block to be removed.

The only way you'd be undergassing the system is if you make the common newb mistake pushing the gas block up against the shoulder rather than offsetting it. With or without the spacer, if the gas block was manufactured to be offset, it must be offset or you'll be partially blocking the gas port. That said, there are aftermarket gas block that are supposed to be pushed up against the gas block (no offset) because the gas port hole in the gas block has be relocated with that in mind.

</div></div>

 

[sled_mack]

Re: Need help - AR10 cycle problem

Well, we made some progress at the range yesterday. With the original buffer, I still got a failure after only 11 rounds.

A friend with me suggested that if it were overgassed we could move the gas block a small amount to offset the port in the barrel with the hole in the gas block. Since I was at the point of needing to send it back to Armalite if I couldn't get it working, it was worth a shot. However, when we loosened the gas block and slid it forward, we noticed that the gas block hole was not aligned with the port in the barrel. The gas block was actually too far forward. I'd estimate the alignment of the holes was probably blocking 60 percent of the port.

While I never moved the gas block (and it never moved based on the marks I put on the barrel), I did buy the gun used.

So, we moved the gas block back to the shoulder on the barrel. As I read just now, that was probably too far. But, I'm guessing that the port is more aligned now than it was before.

Shooting after moving the gas block showed potential results. The brass began landing closer to 1 o'clock position (which is where Armalite told me it should land). I only had 18 rounds left, so I am not claiming it is fixed. But I split those between the normal and heavy buffer, and both seemed to function just fine and both left a pile of brass around the 1 o'clock position, with the heavy buffer a little more like 2 o'clock.

Anyone know the thickness of the washer mentioned by DavidAR10? I'll get a few more rounds through it and check the carbon marks on the barrel under the gas block and see if the port and the gas block are lined up. Worst case, I'd like to try moving the gas block forward by the thickness of the washer and see if that makes any difference. I will say the gas block was forward more than just the thickness of the original handguard cap.

I won't consider this issue fixed until I have a few hundred rounds through it. And worst case, it will go back to Armalite over the winter.

Thanks again for all of your help. I'm learning a lot from all of this.

 

[sinister]

Re: Need help - AR10 cycle problem

The AR-10 gas block shim is .030" thick.

 

[luckyshot27]

Re: Need help - AR10 cycle problem

mine had to be shimmed too cuz i put a freefloat rail.now it cycles perfect,it just doesnt lock the bolt back,but then again i only have 200rds.ill wait till a shoot it a lil more to see if i still have the bolt hold open problem.

 

[problemchild]

Re: Need help - AR10 cycle problem

1:00 is way overgassed and NOT normal. 3:30 is normal

Im sorry but shim a gas block to control gas is just plain stupid!

BUY AN ADJUSTABLE GAS BLOCK AND BE DONE WITH IT!

You never responded to my post on the ejection port brass marks. Are there marks in the front or not? I just spent many months solving this same issue and am not talking out my azz. If you do not want my help.....

 

[sled_mack]

Re: Need help - AR10 cycle problem

Problemchild - not ignoring your suggestion. It was late last night when I read the posts and responded. I'm not ignoring your suggestion, I just didn't get the rifle pulled from the safe to look.

If I need an adjustable gas block, it will likely mean a complete rebarrel. Living in NY, my brake is pinned and welded. If I have to get that cut off just to put on an adjustable gas block, it's getting a more major make-over. But I was really hoping to shoot out this barrel first.

I agree that shimming a gas block into position is a shitty solution. But until I move from this shitty state, I'm limited to what I can do without sending the rifle out to a smith to get the brake cut off.

The general consensus of everyone I talked to is that 1:00 is overgassed. But 2 different people at Armalite told me that is how they set them up when they ship them new or if in for service. So I'll try some more rounds and see what happens.

Thanks.

 

[sinister]

Re: Need help - AR10 cycle problem

Or you can just use a .030 feeler gage for spacing and lock that sucker down tight.

Your original barrel should give you good service before you need to change it out.

 

[Mike_in_FL]

Re: Need help - AR10 cycle problem

I have no idea what your Troy rail looks like so I didn't respond initially. Does it just lock into the delta ring and has nothing holding the muzzle end? If so, did they remove the handguard cap behind the gas block or not? If they did, then you need to feeler gauge your block out from the shoulder as was already suggested.

If you want to try changing the cycling of your rifle without modding the gas system you can try David Tubbs carrier weights.

 

[problemchild]

Re: Need help - AR10 cycle problem

I know of a least 1 manuf. that makes a 2 piece block for just that reason. I think its YHM. Im sure there are others. Do some searching.

So have you had a chance to see if there are brass marks in the front of the ejection port?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sled</div><div class="ubbcode-body">Problemchild - not ignoring your suggestion. It was late last night when I read the posts and responded. I'm not ignoring your suggestion, I just didn't get the rifle pulled from the safe to look.

If I need an adjustable gas block, it will likely mean a complete rebarrel. Living in NY, my brake is pinned and welded. If I have to get that cut off just to put on an adjustable gas block, it's getting a more major make-over. But I was really hoping to shoot out this barrel first.

I agree that shimming a gas block into position is a shitty solution. But until I move from this shitty state, I'm limited to what I can do without sending the rifle out to a smith to get the brake cut off.

The general consensus of everyone I talked to is that 1:00 is overgassed. But 2 different people at Armalite told me that is how they set them up when they ship them new or if in for service. So I'll try some more rounds and see what happens.

Thanks. </div></div>

 

[hlee]

Re: Need help - AR10 cycle problem

Yes, but he still has to get the stock gas block off...

 

[sled_mack]

Re: Need help - AR10 cycle problem

PC - Just checked it. No brass marks at the front of the ejection port. However, I have less than 20 rounds through it since I got the gas block aligned better. Before that, I would have been undergassed and not been hitting brass at the front of the ejection port, I think? I'll keep an eye on it as I run more rounds through it.

Mike - the rails are free floated, so no contact at the gas block. I cut the delta ring off when I put the Troy rails on.

sinister - I would really like to get a lot more use out of this barrel before needing to do something with it. I have no reason not to think I can't still get more life out of it. I'll take some feeler guages along to the range next time and see how it reacts being moved forward .030 from the shoulder.



I'm still confused as to why this cropped up so suddenly. But if I can keep it running, I'll be happy. Shooting this more often has made me a better shooter over just shooting my bolt gun. By the time I wear this barrel out, I should be ready for upgrading to a custom barrel and maybe a better caliber over the .308.

Thanks everyone.

 

[recce556]

Re: Need help - AR10 cycle problem

Ok, I think you left out some key pieces of information here. So let me get this straight, you bought the gun used and it worked fine up until you did your mods. You never touched the gas block prior to the most recent posting but once you did move it, you noticed that it was incorrectly located yet (either from the factory or from the previous owner).

With just nine rounds with each buffer, you definitely can't say if it's fixed as it took 11 to induce the most recent failure.

So now I'm wondering why your gun didn't have a spacer behind the gas block? If it has a pinned barrel (and the previous owner bought it that way), that means it was factory built without a handguard cap nor spacer? Didn't you have A2 style handguards on there before you installed the Troy as the AR10A4 comes with them? Did you cut off the handguard cap too?

Either way, it still doesn't make sense. If you were getting only 60% gas through your system and it functioned fine before the mods and the gas block never moved, your gun should still function the same with factory buffer/spring as nothing in the gas/recoil system has changed. When you were cutting off the delta ring, you didn't nick your gas tube did you?

Do you have picture before you modified it and after you modified it? I think it would clear a LOT of things up.

 

[sled_mack]

Re: Need help - AR10 cycle problem

Sort of - bought it used. Worked fine. Did the mods, worked fine for over a year. About 300 rounds with a 178 Amax load and about 400 hundred with the 168 SMK before having problems.

Agreed, 18 rounds does not indicate "fixed". It indicates "hopeful", at best. As I said, after a few hundred rounds I'll consider it "fixed".

It came with the standard A2 handguard. I did cut the front cap off as well. It was thin enough sheet metal that I cut it with a wire cutter as far as I could, then grabbed each side of the cut with a pliers and pulled it apart without having to move the gas block. The gas tube is not nicked or cut. So that explains why there is no spacer between the gas block and the shoulder on the barrel.

I agree that something doesn't make sense. I can't explain why it worked for so long then can't go 15 rounds without a failure. And it was only luck that I marked the gas block when I did the handguards in case I had to move the gas block and never cleaned the mark off. Until we moved it Sunday, it was still lined up as it was since I marked it last year.

The only remote possibility I can think of - with the gas port blocked so much, it was on the edge of operating. Could some dirt have gotten in there and pushed it over the edge to not working? Maybe it's possible. With the pressure and heat in those gasses, it seems like it would be almost "self cleaning". Using a small pipe cleaner in the gas tube, there isn't much dirt coming out on the pipe cleaner.

And I'm still suspect as to why the bolt doesn't move freely in the carrier when removed from the rifle? Should it? I know it's a subjective thing, but how free should it be?

 

[sinister]

Re: Need help - AR10 cycle problem

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">When I did the mods, I was using a 178 Amax. I changed to a 168 SMK, LC brass, and 45.5 grains of Varget. The rifle ran the first 300 of the 168 SMK loads with no problem. Now I can't get 20 or 30 without a failure.</div></div>

I still think your charge is too high.

 

[Graham]

Re: Need help - AR10 cycle problem

Agreed: That's a hot load and Varget is way too slow for that gun.

 

[BCP]

Re: Need help - AR10 cycle problem

I had this happen on an AR15 it would eject at 330 but every 15th or so spent case would stay inside the action (on top of the mag sometimes duobling up and jamming with new cartridge from mag). A new extractor spring/rubber o ring thing fixed it.

If the bolt locks back on last round I'd think you have enough gas pressure to operate the action.

 

[maggitas]

Re: Need help - AR10 cycle problem

I would have a gunsmith go over the weapon. You may want to check the headspace on the rifle.