Aero M5 (AR 10) jammed up - what do you make of this failure?

[riffraff]

I've got a 20 inch barrel Aero M5 in .308 I've been playing with as a longer range shooter, is attached to an Aero lower, Aero nitride BCG.

I got it home, cleaned barrel & BCG, oiled BCG and upper real well w/ hoppes synthetic, and first outing ran it a light 30 rounds or so, took it home, cleaned & oiled everything again.

Today I was sighting it in - ran ~80 rounds without a failure of any sort then got a FTF, ejected the live round, kept going, few rounds later got another FTF and when I went to eject it I found it was jammed.. Step 1, dropped the mag out. Tried to pull the charging handle and it was stuck.

Manner it was jammed was as follows, sorry excuse my terminology if wrong - bolt was fully extended in the BCG, however there was a full 1/4 inch between the live round and the bolt. The round was "loose" in there, not stuck in any manner, you could slide it in and out of the chamber by tilting the rifle..

I tried pulling on the charging handle and it was stuck, could not get the BCG back. Was about to pack the rifle up just how it was and take it to a smith later then decided the safety aspect of it I was not happy about so pulled harder on the handle and it slid back, locked it back, dump the round out, then slowly let it go forward and it went into battery no issues.

I can manually slide the bolt by hand, don't see any marks inside of the upper to indicate why it jammed, BCG is still well oiled, have not taken apart the BCG yet but I expected something catastrophic the way it was stuck and I just can't find anything wrong..

Both of the FTF rounds I found were not contacted by the firing pin, as it seems what goes wrong is the bolt is not sliding back into the carrier during these failures. But I don't understand how the seemingly hopeless jam is related to the bolt not sliding into the carrier, seems more like a symptom of the carrier jamming so the bolt isn't making contact with anything.

What do I do - clean it and re-test? Call Aero? Have a gunsmith take a look? Thanks in advance!

[stagpanther]

Hard to tell-especially without pictures--but it sounds a bit unusual that your getting a jammed bolt while the cartridge is actually loose in the chamber--first thought that comes to my mind is something might be off with your bolt cam pin. I would take the BCG apart (disassemble and clean) and ensure that everything is fitted and functioning properly. look for signs of wear on the edges of the cam pin as well as the cut-out in the upper--if it's hanging up there should be obvious signs. A badly installed firing pin retaining pin--or even a distorted one, can also cause problems. I once had a carrier that the slot for the cam pin had too much of an unfinished edge on it--so the cam pin got hung up on it and couldn't rotate properly--though that was probably a manufacturer's incomplete carrier that somehow got out the door and found it's way to me before being properly finished (I'm just lucky that way).

That's my first guess, considering you haven't mentioned anything like short stroking, failure to eject etc.

[Mobuck]

Did you grease the cam pin and it's track? Sounds like it may be galling causing the BCG to hang up.

[riffraff]

I don't use any grease, only oil, but cam pin is certainly well oiled. Was taught oil and never thought to put grease - is that a standard thing to grease these or a debated topic? I am kinda big on cleaning, every time I shoot a rifle I clean it before it gets put away or used again.

Just took the BCG apart now..

Soooo #1 - I know I put these things in real evenly spaced, but the gas rings somehow are all lined up... #2 there are some scratches - can't feel them but can see them - which seem to indicate the bolt/rings scraping along within the BCG, one at 12:00 and one at ~7:00.. The one at 7:00 might line up with the extractor pin but extractor pin seemed to be in there OK and shows no wear, no idea what would cause scoring at 12:00, nothing there... marks could also somehow be metals painted on there or manufacturing blemish, can see the marks but they are small enough I can't feel them.

Wear around cam pin strikes me as maybe little odd for a basically new BCG too but if there was 1000 rounds through this rifle and not barely over 100 I would not think anything of it..

If it might help can try to take some pictures of the BCG parts and get them up there this week.

What do you figure I should do? Clean and re-test this BCG?

Thanks!

[marine6680]

An AR can run with a single gas ring...

Stagering the gaps is a myth... Don't worry about that.

Grease on sliding parts or parts with shear forces is a rule of thumb. Just using a quality oil in an AR is fine though. Don't use thin oils in an AR... Something like Remember oil is too thin. The oils should flow, but with a little resistance. If it's like water, it's too thin.


Pics would help a lot.


Others who have had a problem like you describe, have had the firing pin retaining pin break and jam between the BCG and receiver wall.

You describe that the bolt was not in the barrel extension, so I don't think it was the bolt binding.

It could be an issue of binding with the Cam pin in the upper.

Or it could be an issue of the bolt not fitting well in the carrier.

The gas rings could be binding. If one pops out of place, it can catch in the carrier and bind.

My fiance's rifle likes to shear the rear gas ring... It runs fine, but I should probably see about replacing the carrier and or bolt.

[Mobuck]

" Was taught oil and never thought to put grease - is that a standard thing to grease these or a debated topic? "

You're not taking the rifle to war in the sandbox, right?
You're shooting in warm weather at paper, right?
You want to break the rifle in and smooth out the wrinkles, right?
In that case, there's no logical reason not to use grease on the cam pin.
Debated topic, probably so.
Advice from someone who carries an AR 24/7/365, grease the cam pin unless you're hunting in -20* temps.

[HiBC]

Just curious,does this rifle have a forward assist?

[stagpanther]

Just curious,does this rifle have a forward assist?

Good point--I too thought about correct pawl installation.

[jonnyc]

"have not taken apart the BCG yet"

Your first mistake.
Guns are generally shipped in preservative, not lubricant. In addition, parts like BCGs can be machined or assembled incorrectly. Your bolt might have jammed within the BCG or you might have missed some unknown "foreign" bits or damage.

New guns should always be disassembled, cleaned, inspected, and lubricated. Good rule-of-thumb to follow.

[stagpanther]

To the OP--what does your brass look like? the rounds that were not chambered properly--were they loose in the chamber even before you tried to extract them? I've had a couple of the older M5 Aero lowers that had sightly different buffer tube collar dimensions and as a consequence they didn't quite line up right with standard DPMS style upper's charging handles--one of them the charging handle couldn't clear the back of the lower without inducing an an angle--which threw the functionality of everything else in the cycling.

[riffraff]

Thanks for all the input guys!

A few things: I did strip, clean, and lubricate the BCG like I always do prior to shooting, then again after the first time I shot it. I just didn't immediately take apart the BCG upon this failure since I was trying not to obscure any evidence that would help me figure out what was wrong.

As far as greasing the pin - I got no problem doing that if it's a better idea, I just never thought to do it as I just always used oil (hoppes synthetic) and been under the impression that was a fine way.. What grease should I be using on this? Or if my oil choice is poor, what oil is good?

For me a key thing with oil is (which is why I like the synthetic) something that does not burn off and create a hard carbon mess, so the parts are easier to clean without so much abrasion... And of course something that lubricates is good. I learned over time the oil I'm using seems to be a bit better but really got no idea. I got no problem switching this stuff up - do not claim any expertise and that's why I'm asking.

Here are some pictures - pin shows the friction which was occurring, not really sure if I can make a whole lot of it, maybe you can. Hard to get a good picture inside the BC but I tried. The worst marks on the pin I can feel, the marks inside the BC I cannot feel at all.

Lower I'm using I bought within the last 2 months, CH, BCG, and 20 inch upper (.308 5R model from Aero too) all bought recently. Every seemed to run like a sewing machine right up to the 1st and 2nd failure, no binding I can detect.

Also posting pics of rounds - if you want something specific please direct me! Thanks in advance!

[riffraff]

More pics..

[riffraff]

Last pics..

[riffraff]

Oh and yes the rifle does have a forward assist, was bought as a complete upper from Aero.

Literally where the BCG stopped when it jammed was with the bolt extended, and a round that had 1/4 inch of play between the bolt and the end of the chamber. So it scooped a round up, threw the round into the chamber, but the bolt itself stopped short, and was stuck there to the point where I had to pull with some force on the CH to get the BCG to come back, then when it got free seemingly everything was moving OK as if nothing was wrong.

I guess I should mention too - if it helps somehow, I have a new spare BCG sitting here, could compare or even try to run with it.

[stagpanther]

Still hard for me to tell what's going on--but your brass is looking damaged on the sides--and since a locked bolt would dimple your primer even without firing--my guess is that your bolt is failing to go into battery altogether--but the mystery is why this is "once every 30 rounds or so."

First thought--ditch the perfecta stuff and get quality ammo--preferably a hornady match eld or federal 168 matchking. Carrier assemblies shouldn't need "tender loving care" if they are assembled correctly--do what the aero manual tells you to do--though I personally wouldn't be globbing anything on it except maybe adequate lubricate on the outside of the carrier.

Get a dummy round or snap-cap and cycle the cartridge with a range from "full-power drop the bolt" to slow feed from the magazine. It's hard for me to tell--but the scratches on the sides of the cases look like the cartridge may be going in at too much of an angle and is hanging on the edges of the extension lugs on the way in--OR--the cartridge may simply be stripped from the magazine at too much of an age for some reason. Try a different magazine (I've never had a brownells magazine fail--and bonus--they are among the cheapest).

[stagpanther]

Takes a while for my brain to work.

First things first--remove the upper assembly from the lower--pull the charging handle back so that the bolt rotates and disengages the extension--does it do so without much resistance?

slide the charge handle back to where the handle stops (the bolt head should be just past the assist hole) That movement should be smooth, easy and straight.

Pushing the rear of the carrier, slide the bolt to where it contacts the barrel extension--at that point the back of the carrier should be roughly 3/8" past the end of the upper receiver. Now push the back of the carrier--the bolt should rotate and engage the barrel's lugs with a bit of resistance--but not much--it should be an easy "pop" for the bolt to fully close. The back of the carrier should be almost perfectly flush with the back of the receiver.

If your carrier does all these things with no problems--then your issues probably lie elsewhere than with the upper (with the possible exception of "gas funkiness"--which I kinda doubt unless your ammo is possibly doing something weird).

[HiBC]

I don't have the answer.

IMO,its significant that the BCC stopped when the cartridge was free to move.
All thingsabout cartridge being stuck in thechamber are eliminated.

How many other things can lock up the BCG ? Not many.

Off center or bent gas tube?

Something about the forward assist ?

Something with the buffer tube,buffer retainer plunger,etc?

Mystery.

[riffraff]

Thanks and gotta try that test later..

Couple other things, reason the firing pin makes no contact is I think it can't until the bolt retracts, right?...

And then it wasn't a once in 30 round failure, it was perfect for 100 rounds or more, then an ftf, then round or two ok, then the jam.

Maybe it's got something to do with ammo, most of what I ran was pp and probably better but switched over to the cheaper stuff when running low, first time I used it in anything maybe.

[stagpanther]

Couple other things, reason the firing pin makes no contact is I think it can't until the bolt retracts, right?...

That's why I think your cartridge never went into battery--which you seem to indicate was the case.

AR's can do funny things at times--might be more than a coincidence this is associated with the ammo you switched too.

I have a question about your bolt cam pin. In the photographs I can't tell for sure if it's just the lighting--but it looks like one side is dark with the nitride and the other side looks bright with the nitride worn away--is that how it really looks?

[Mobuck]

"What grease should I be using on this? "
I'm using from a tube of "RED-TEK" wheel bearing grease that I opened probably a decade ago and still 3/4 full.
Grease the cam pin and track and bolt lugs on a new rifle.
Apply CLP to interior of BCG until nearly dripping.
Work the BCG by hand until the bolt will close and lock by it's own weight when the upper is held muzzle down @45*.

[riffraff]

I'll get some more pics up on the cam pin so we can focus on that a bit.

The cam pin I do not believe is actually nitride coated, is a duller color, still seems smoother than phosphate, but is not the true black and shiny color of the BC. The coating is more of a grey, seems thinner.

As far as the coating though - has wear marks through the coating. like little claws that come down from the "head" of it, and there is a bit of a ridge I can detect along the bottom side of it where it is wearing on the BC. So there are shiny spots where the friction is, but they are not even, and it is not taking all the coating off rather it looks like what happens when you run sandpaper over a bumpy surface and it gets feathered out if that rings a bell.

[riffraff]

Mobuck - thanks for that, will go dig around and see what I got for benign grease. Most of what I stock is some sort of marine grease, bearings, reels, special outboard crap, not sure what additives are in there that will go bezerk in a rifle .. I suppose I could just hit the local gun shop on the way into work tomorrow - one of them I pass has a huge section of gun care liquids I'm sure they have a grease.

[bfoosh006]

ALG Go-Juice is what you seek.... Every thing Fire Clean claimed to be.. ( but wasn't )

As for the out battery issue... try some other ammo... and did you thoroughly clean the chamber. Prefecta... isn't the most QC known ammo out there.

Do you have all the fired cases ? ... any of them missing a primer ?..maybe one poped out and jambed up the works.

Any photos of the fired cases ?

And I don't use grease on my AR BCG's ... no where does Uncle Sam say to, and it has worked A-Ok for me for decades.

[stagpanther]

There is a small cut-out in the upper receiver along the track of the charging handle where the cam pin "head" rotates--do the edges of that cutout show any obvious deformation (which could indicate the cam was jamming in it)?

[Mobuck]

OK
Here's another answer to the live round sitting in the chamber but bolt not locked(beyond the possibility that the bolt pushed the round ahead of it into the chamber but seized before it closed/locked). I have seen badly set up AR's in .223 that had enough residual gas in the system that the bolt would nearly close but then be forced back by this residual pressure but neither far enough to pick up another live round or enough to build spring pressure to re-close/lock the bolt on the round it had already pushed into the chamber. This often left a live round in the chamber with the bolt sitting against the case but extractor not engaged.