Palmetto PA-10 failure to eject

[W.E.G.]

2 hours ago, 98Z5V said:

Look at that square-faced ejector...    This thing mis-feed alot?  The square shoulder on that ejector needs to be rounded - or it's gonna be hell with every round that feeds from the right side of the magazine.

All the feed problems were cured 100% after replacement of the Palmetto extractor with the Fulton extractor.

[98Z5V]

Here's what an ejector should look like - no square shoulders on it.  Squared up ejectors have big issues feeding rounds from the right side of the magazine...  Little known info, for proper ARs, but it's true as hell for the people that make ARs that need to function all the time, every time.  Right side of the pic is a shiit-ejector.  Left side of the pic is what a proper ejector looks like.  This is what separates a budget-gun from a reliable-gun...

Attention to detail...

 

Edited July 28, 2019 by 98Z5V

[W.E.G.]

Three pics of the locking lugs on the barrel extension:

[W.E.G.]

It was mentioned that the SCAR series of rifles require that the Magpul PMAG be modified (widen slot in back of mag) in order to keep the magazine body from causing the bolt-hold-open device to ride up when the magazine is inserted.

This does not seem to be the case with the PA-10.

Here, with the guts out of the mag, I can insert the mag-body and wiggle it around without causing any movement of the bolt-hold-open device.

[W.E.G.]

Some PA-10 owners have complained of the bolt carrier slamming into the rear of the receiver, and cutting gouges in the threads for the buffer-tube (receiver extension).

Mine does it a little bit. But really only a very little bit. I think mine did this on the first outing, and the condition has not worsened at all since then.

[W.E.G.]

A question was asked about the firing pin.

The tip of the firing pin measures 0.080" and it appears undamaged.

I'm not having any issues with pierced/blanked primers or "volcano" primers swelling back into the opening in the bolt.
So far, I've fired Santa Barbara surplus ball ammo, and a couple handloads (41.5 IMR4895 with 168SMK and 40.5 IMR4895 with 173-grain "M118" bullet).

[W.E.G.]

Getting back to the issue of the lugs on the barrel-extension, I highlighted the pic to show wear-marks on the lugs.

I'm not sure what is the best terminology to use to describe the locations of the wear-marks.
I guess I'd say the deepest marks are on the "clockwise" faces of the barrel-extension lugs. 
However, if you look closely less-prominent wear-marks exist also on the opposite-side faces of the barrel-extension lugs.

Somebody brought up the issue of whether the barrel extension may not be ideally "timed" relative to the timing of the bolt.
I guess this is some evidence that the bolt is not perfectly timed, to wit: the bolt appears to be timed slightly counterclockwise relative to the lugs on the barrel extension.
Therefore, the clockwise faces of the barrel-extension lugs are giving the bolt a beating as the bolt negotiates the barrel extension.

It was also asked whether there appeared to be any slop in the slot on the upper receiver. 
The idea being that such slop would allow the barrel to shift clockwise/counter-clockwise, and that could cause the bolt to have to beat its way around the lugs on the barrel-extension in an inconsistent manner.
I did remove the barrel from the upper receiver for inspection. I was impressed with the tight tolerances - especially the tightness of the barrel extension in the cylindrical part of the upper receiver.
During that disassembly/inspection/re-assembly I wasn't specifically looking for slop in the slot/barrel-pin engagement. 
But, I'm confident that I would have noticed significant slop in that dimension if it had been present.

[W.E.G.]

As I sit here pondering this, I'm beginning to feel fairly certain that this is the situation:

The bolt and the barrel-extension are not "timed" correctly relative to one another.
As the bolt moves into battery, the leading edge of each bolt-lug impacts the clockwise-face of each barrel-extension lug.
This impact batters the leading edge of each bolt lug, causing the each bolt lug to carve a channel into each of the corresponding barrel-exteinsion lugs.
As an "impact-channels" are created, metal on each barrel-extension lug is displaced to form a burr on the chamber-side of each barrel-extension lug.
The burr on the chamber-side of the barrel-extension lug then chisels the trailing edge of each bolt lug as the bolt unlocks during cycling.

I wonder whether this violent mis-timed relationship between bolt and the barrel-extension will "wear-in" to a point where the damage caused by each cycle of the bolt will be less?

This raises several other possibilities: 

Is the mis-timing due to the timing-pin-slot in the upper receiver being cut out-of-time, or is the mis-timing due to the pin in the barrel extension being located out-of-time? 

Is the mis-timed relationship a product of "stacking of tolerances" where both the timing-pin and the slot in the upper receiver might be each out-of-time (in opposite directions)?

Could there be a third timing-factor?: Is the channel in the top of the upper receiver mis-timed (this is the channel which guides the key on the bolt carrier as the carrier reciprocates)?

Or perhaps a fourth timing factor?: Is the central "tube" axis of the main channel in the upper receiver not true relative to the "tube" axis of the barrel extension?

[RedRiverII]

Terrific posts gentlemen,  I'm interested in the answer.  I did have to wait for my mind to appreciate the photos,  much like your camera focusing on the targets earlier in the thread.  Once I did focus enough I realized the barrel extension lugs were beat up badly.  Just conjecture on my part but there seem to be chips taken out of the steel. If the two parts were slamming into each other I would expect to see roll over edges,  not chips.  Roll over, like what happens to a chisel head after a while.  Could it be a combination of new chamber shards and crumpled brass causing this? Or the roll over steel on the lugs breaking off and then tearing into the right hand or clockwise portion of the lugs?  It was a new rifle correct?  Keep in mind I'm new at this and find this thread educational.  Thank you.

[RedRiverII]

Best response I've found so far,  and he is a class act compared to others that posted in this particular thread,  not from 308ar.

 

"Caused by tolerance stacking. Factors involved include barrel alignment pin notch, gas key/charging handle channel width (where the cam pin rides in the upper) and of course cam pin width. 

If the barrel truly looks centered (which it is not based on the pics), not likely your alignment pin notch, but don't dismiss this entirely.

If the cam pin running area in the upper allows too much play of the cam pin, only real option is replacing the upper if you really don't want these marks. 

If the cam pin is too narrow on it's own, that's an easy replacement. 

If it's a stacked factor of all three, then a minor change in any one of them can alleviate this issue. Easiest to do is to find a cam pin with a wider head followed by disassembling the upper and re-torqueing on the barrel. How you do this will dictate the direction the barrel wants to "rest" when done. Use a reaction rod system and the barrel will naturally cant to the right (OPV). Use receiver clamshell and the receiver will naturally cant to the left. 

If re attaching the barrel clears the issue up but the feed ramps don't appear aligned, no worries. Not a big deal. There's always a chance the feed ramps were machined slightly offset as well, and if the builder used the feed ramps as their alignment "gauge", then the whole thing would be off. 

Personally, i'd re-torque the barrel to clear this issue up. I wouldn't allow this kind of work out of my shops over seas and I certainly don't allow it when I work on guns for people here at home either."

[W.E.G.]

On the suggestion that the timing of the barrel-extension and bolt could be out of whack, I removed the barrel nut again.

The slot in the upper receiver for the index-pin on the barrel-extension is quite narrow, and allows almost no lateral movement.
See the video below.

I used a Brownells reaction rod in conjunction with the Wheeler Engineering upper receiver action block to make a very small timing-adjustment.

Click link below to view one-minute video

https://youtu.be/iUXljAs2tiQ

Edited July 29, 2019 by W.E.G.

[W.E.G.]

Sorry, I forgot to hit "publish" on the youtube site before copying the youtube link in the previous post.

[W.E.G.]

For the benefit of readers who may be less-experienced  with the tools involved, here is a pic of the Wheeler Engineering tool grabbing the upper receiver by the Picatinny rail.

The Wheeler tool gets clamped in a vise.

Here, I'm using aluminum jaw-covers to keep the vise from marring the tool.

The tool is basically a slotted piece of aluminum that slides over the Picatinny rail, and which is compressed by the vise to provide a very firm grip of the upper receiver while you wrench on it.

[W.E.G.]

This is what the "reaction rod" devise looks like when it is married-up with a 1/2"-drive breaker bar.

When engaged into the lugs on the barrel extesnsion, this gives the leverage that allows you to tweak the timing of the barrel in the upper receiver just a smidgen.

Close-up of lugs on reaction rod that engage the barrel extension lugs when doing this process.

[W.E.G.]

I wish I'd played-around with the bolt/carrier assembly right before making the adjustment, to get a feel for what amount of friction or contact I could feel before makeing the adjustment.

After I made the adjustment, I could not feel any dramatic impact or friction.

I do wonder whether I made any actual change in the timing, as the direction I moved the timing today is the same direction that the barrel would normally move when tightening the barrel nut.

Speaking of the barrel nut, I can say the barrel nut (Michigan Industries I believe) on this upper does not like to be removed, re-installed, re-torqued repeatedly. I could tell that the threads were starting to shed some anodizing on re-tightening this nut now for the third time in the life of this upper. There was some grittiness that could be felt while tightening the nut today. At first-engagement of the threads, the grittiness was giving me a real scare. Really was acting like it was trying to cross-thread. Maybe I stretched the threads a bit on the previous removal/replace. 

I was able to get the situation under control without actually cross-threading. But, I caution it was touch-and-go for a couple minutes. Replacement Palmetto uppers can be acquired if you ruin one. I haven't seen a source for replacement barrel nuts for this exact handguard if you bugger a barrel nut.

My advice is don't get the notion that you can take that barrel nut off-and-on repeatedly without encountering problems with the threads.

[Ravenworks]

I have all these tools for both sizes of the platform.

Just curious what you use that pin on the top of the barrel extension for?

[W.E.G.]

The index pin is furnished with every AR-type barrel I’ve ever seen.

[shooterrex]

That pin fits in a slot on the upper receiver. It locates the barrel to the proper location.

 

[98Z5V]

If the lugs on the barrel extension aren't lined up in the receiver, you have a manufacturing issue with the barrel manufacturer.  There are several steps in making a barrel for an AR that are followed.

First, the index pin does not, ever, lock a barrel extension to a threaded barrel.  The index pin only goes into the extension, and doesn't, ever, go deep enough to get into the threads in the barrel itself.  It's simply a locating pin, in the extension, to center the barrel.  Many people think the index pin locks the extension to the threaded barrel, and nothing further from the truth, will you find. 

So, step one, if you're already working with a barrel blank profile that's finished (outer contour) and rifled.  The barrel extension goes onto the barrel at 175lb/ft.  Not a typo.  Most barrel extensions are already machined with the index pin exactly 180 degrees from the feed ramps, before they ever go on a barrel.  That puts the feed ramps at the bottom, and the index pin directly at the top - so when you mount it, your feedramps are directly centered at 6 o'clock. 

Hey, maybe your barrel maker didn't have a drilled index pin location on that extension, had to do it himself, and was off by a degree or two.  Not common, though.  Usually not a "gunsmith job" unless your gunsmith is making the extensions himself.

Step 2 - if you have an extension that wasn't drilled for the locating pin - you index exactly 180 degrees from the feedramp center on the bottom, and drill the locating pin hole into the top of the extension, 180 out from that.

Step 3 - barrel extension is already torqued to 175lb/ft, you have barrel index pin location, you now have barrel centerline, .  You drill the gas port directly in line with the index pin, which is on barrel centerline.

Step 4 - chamber the barrel.  ream the chamber to set the headspace, according to that barrel extension that was properly torqued onto the barrel at 175lb/ft, then the rest of the barrel was machined.  Chambering is the last step.

So, could something have gone wrong in that process?  Maybe.  Is something machined "off?".  Maybe.  Was is assembled incorrectly?  Maybe.

Something isn't right, though, the way that thing is chewing up your bolt lugs.  Those are horrible - that wear isn't even normal.

Take advantage of the PSA Lifetime Guarantee, and send the barrel back, and ask for a replacement of the bolt - which is fubar'd.  

 

 

[W.E.G.]

Fired another 100 rounds today.

Good results as far as accuracy and function.
Might post more pics of the bolt when I get around to cleaning it.

Here we have 10 rounds fired prone, sling-supported, 100 yards.
I called the low shot. Looks like I lucked out and still clipped the 9-ring.
Not sure if it scores a 96 or a 97. That one shot 8:45(ish) may or may-not have clipped the 10-ring. Even when I peeled-off the mini Shootn-N-C, still can't tell.
I called that wide 9 left too. Didn't think it was that far when I let it go. But, it is what it is.
I have a harder time calling the high/low shots as high or low. I'll keep working on that.

Not all the targets were this good, but the problem was all me when I flung an 8 or a 7.

[W.E.G.]

Here are a few pics of the condition of the bolt after yesterday's 100-round outing.

I decided to shoot the pics before cleaning. May better-highlight the wear-points.

[Sisco]

A workable rifle now. Congrats

[W.E.G.]

Thanks.

Should be interesting to see if this bolt continues to take the beating. I keep waiting for an entire lug to snap-off.

[jtallen83]

46 minutes ago, W.E.G. said:

Thanks.

Should be interesting to see if this bolt continues to take the beating. I keep waiting for an entire lug to snap-off.

Please don't use it anymore. Your hands, eyes, possibly life are more important than anything that can be proven by driving that bolt to failure. 

[W.E.G.]

Let's think about this for a minute.

If one lug breaks, what happens?

Plenty of accounts of that happening with AR15 guns. Thousands of accounts actually.

Bolts break in two at the cam pin too.

Its a testament to the design that we never hear (or at least I'VE never heard) about bolt failures that cause injury to the shooter.

I'm not indifferent to the concern. And I appreciate your concern. I'll monitor it closely for now.