I have an AR-10 with an Aero Precision upper which worked well and now it doesn't and I hope someone in this knowledgeable group may have a solution. Thanks for taking your time to read this.

When the bolt catch is released and the bolt carrier group advances forward it strips off a .308 round and inserts it partially into the chamber. The BCG does not seat completely leaving about 1/4" of space open. The bolt assist does not force the round forward and it is a BUGGER to pull the charging handle back to lock open the BCG. The round is not unduly difficult to remove from the chamber and all that is usually needed is to tap butt of the rifle on the bench to shake out the round.

I have taken the upper to a gunsmith and he diagnosed a loose gas tube and this was replaced. I have inspected the chamber and do not see an obstruction. The bolt has been cleaned, lubricated and the bold rotates and the cam pin is smooth.

I'm scratching my head. Is my ammo bad? I've checked.

I've thought, do I have a round caught over the bolt? As hard as it is to pull open the bolt charger there may be something stuck in there but I don't see it.

Any ideas? I'd appreciate your suggestions.

Have you tried different ammo? Does the bolt close ok on an empty chamber? Just trying to narrow it down.

Yes, I've tried different ammo with the same results. The bolt closes completely without a cartridge in the chamber.

It is chambered in .308 right?

That is an excellent question. It is not acting like it is chambered in .308 but it shot .308 before and now it won't chamber the .308 round. It makes me think that either there is something stuck in the chamber (like a partial shoulder of a case) or the bolt is being blocked.

The bolt, with out a round in the chamber, closes completely so I don't think the bold is blocked. It's difficult to see into every nook of the chamber but I can't see something in there.

Does the bolt carrier move into place slowly without buffer spring pressure, and no bolt head? With bolt head?

Yes, the bolt carrier, with just pressure moves into place. It does hesitate before the "snick" when the bolt locks and I've wondered if it was functioning. I haven't removed the bolt head from the carrier but it moves so smoothly into place that I believe the bolt carrier with the bolt is not the problem.

When I place a cartridge into the chamber and move the BCG forward it fails to "lock".

I think my next step is to use a bore scope to check the chamber. I may get a .308 gauge to see if something is amiss. The fact the .308 cartridge fails to fully enter the chamber may be the clue.

When all of this started, I was at the range and would load the magazine and then close the action. When I pressed the trigger the rifle would fire but the next round would not fully lock though I did not have a "dead" trigger.

The longer I go as I think about this I'm starting to consider this as not just an annoyance but a safety issue. If the trigger will function and strike the firing pin while the gun is out of battery it seems this is a major league risk.

I'm the farthest thing from a gunsmith, and I don't have enough experience with the function of the AR 10 platform but every other semi-automatic firearm I've had experience with will not have a functioning trigger unless the action is fully closed.

I had an aero AR-10 that did the exact same thing. Found out that someone put two orings around the extractor spring. This was making the extractor too strong to latch on rim of the cartridge.

It's a shame there isn't an emoji showing a nuclear bomb going off in someone's head. Thank you for taking the time to share this experience!!

I took the bolt apart and there were two O rings. I removed one of them and reassembled the bolt carrier group. I put a .308 cartridge into the chamber and allowed the BCG to go forward and it closed fully and locked. I will return to the range next week and see if that fixed the problem...

My thanks to yous for your advice.

Bill

I'm certainly no gunsmith but if it were my gun, I would want to take a very good look at that chamber (preferably with a borescope). I wonder about part of a case neck being lodged or maybe a very dirty or scratched chamber.

I can't speak about the AR10 but most AR15s will have 3 gas rings on the bolt. I can't imagine why an AR 10 would have fewer.

Not trying to be a smart a** but is the gun clean and lubed ?? I don't think a person can diagnose anything in a dirty/dry gun.

Best, mike

quote:

Originally posted by mike28w:
I can't speak about the AR10 but most AR15s will have 3 gas rings on the bolt. I can't imagine why an AR 10 would have fewer.

They're talking about O-rings, not gas rings.

Many manufacturers and private builders will install an O-ring on their AR extractors, under the rear of the extractor and around the extractor spring. This adds extra tension to the extractor. This helps compensate for overgassed guns, to prevent the extractor from slipping off the rim during cycling and causing a FTE. It also adds extra insurance against weakening extractors from the extractor springs wearing out and causing similar FTE issues.



In this case, it appears Aero may occasionally be adding two O-rings, which overly tensions the extractor and prevents it from being able to slip over the case rim during feeding, thus preventing the OP's bolt from fully closing.

One O-ring is fine, but two is too many.

I suspect, having removed the second one, that OP's rifle will work fine now.

I have never heard of 2 O-rings on an extractor spring but it's not hard to imagine that the gun would act exactly as described. I learned something new, thanks !!

I think Aero AR10s come with 2 O-rings on the extractor spring. Some think it contributes to more damage to the brass. I hadn't heard Aero does this to compensate for overgassing.

I have a fresh built Aero AR-10 in 6.5 Creedmoore and with limited testing it isn't hard on the brass. I haven't checked on number of O-rings on the extractor, but maybe its fine with two when the rings are new and pliable, and it causes problems when they age and get harder.

This was related to extraction problems, but it sheds light on the double O-ring setup and some extractor tuning suggestions. A response from Aero:

"Good Morning Zeke,

Thank you for reaching out to us today.

Thankfully the fix for this should be very simple, as it looks like your extractor is exerting to much pressure on the brass, so the ejector isn't able to kick them out

If you remove the extractor, you'll see the main extractor spring, with a smaller spring in the center and two black rubber o-rings around it.

The o-rings are there for tuning your extractor for different types of loads. Go ahead and remove either or two o-rings. I'd start with one to see if the issue is solved, but if improves but not completely solved, remove the second one as well. You can dispose of the small center spring as well.

This will lessen the extractor pressure and allow it to actually let go of the brass.

Rest assured, this problem is completely normal and should be solved by the simple steps above."

Wow, so Aero is really including dual O-rings and dual extractor springs as standard?!

It seems like it'd be rare for an AR of any flavor to need all that, so why is that their default? Are Aero's uppers just significantly overgassed from the factory?

Seems like it'd be more straightforward to go with the now-standard single spring and single O-ring, and then perhaps provide a second spring and O-ring for fine-tuning in the low probability chance that they might be needed?

Wow, that is great info on the o rings. Good thing to remember just in case. I was thinking a case head separation or something like that, that might have left a piece in it. At least the bolt closes now with a cartridge in it. Hope for a range report.

Here is a thread discussing extractor tension and how to alter it. There is also a spring use guide lifted from Sprinco. Seems longer and heavier barrels need less extractor tension.

https://www.ar15.com/forums/ar...tiffness/121-716004/

Im having the same FTE issues on my PSA AR10 308 upper. I think I have a GEN 1 or GEN 2?

Range Report

I was able to return to the range Friday Morning. I had removed one of the two O rings which Aero Precision had placed on the extractor spring. Because a .308 cartridge would now fully seat in the chamber and the bolt would close in battery I was expecting the problem to be solved.

Sadly, the same problem repeated itself. After firing the first round a classic Type Three malfunction occurred with a failure to extract and the bolt jammed hard and difficult to move to the open and locked position. I will say that opening the bolt with the O ring removed was MUCH easier than before. The rim of the case, which did not eject, was nicked and scarred. I tried again and had the same result.

I went home, removed the second O ring and went back in the afternoon to try it again. Same results.

I will say that actually shooting the rifle is very satisfying. At the 200 yard range the two rounds I fired hit the plate and recoil was pleasant. Small satisfaction, I now have a semi-automatic rifle with the firing rate of a muzzle loader.

I called my brother. We bought the uppers at the same time from AP. Apparently, he never throws any paperwork away, "I've got the original invoice for the uppers, here's a phone number you can call". It hadn't occurred to me there might be a warranty or factory service available as our purchase was made six years ago. A phone call to tech support wasn't possible but they had a chat box. I explained what was happening, the tech guy pointed me to a warranty claim form which I filled out and submitted. I haven't heard back, I'll let you know.

You can go a long way on hope. I was quite discouraged after I returned from the range yesterday afternoon but I'm again looking forward to solving this problem. It may be I've invalidated the Warranty by removing the O rings and replacing the gas tube. If it costs me money to have the manufacturer fix this problem, at least they have the expertise to do it correctly.