Brass marking on extraction (and blown primers)

[gatordev]

Hoping for a little guidance, as I'm sure this isn't new, but my issue is complicated by having a second issue at the same time. I wouldn't be surprised if the two issues are unrelated, just coincidental.

First Issue:

I had two (that I'm aware of) blown primers today. Unfortunately, I'm not sure if they happened in the same rifle, as only one resulted in a malfunction (I think). My initial concern was any damage to the extractor(s) after they blew. Interestingly, both rounds were CBC 77gr MK262, which I haven't heard of issues with before (unlike IMI). The actual issue wasn't noticed until after all rounds were fired and I found two cases that showed blown cups.

Second Issue:

At some point today, my brass started having scrapes on the backside of the case from the lip towards center of the primer cup. I didn't really notice this until after I discovered an expended primer sitting on my shooting mat, but after looking at the other brass, not all of the brass had the mark, but enough of the brass had it that would indicate it came from both rifles (total of 50 rounds fired, across two different ammo brands). Here's an example of the mark (image is a little larger to help with rez to see the mark):

https://live.staticflickr.com/65535/48717900568_a365a3bcc2_h.jpg

I disassembled and cleaned both bolts (one Fail Zero with 1300 rounds and one Colt with ~4000 rounds). Other than some gook on the extractors, they both looked healthy. So, think this is unrelated? Is this just the extractor slipping? If so, I have an easy fix, but first wanted to diagnose what might be happening.

[SINNER]

That ammo is over pressured. Ejector/extractor marks on the head of the case are indications of slight overpressure. Blown primers are severe overpressure.

[alamo5000]

Definitely looks like a over pressure problem. I would clean your chamber on the rifle first and inspect it just to make sure.

I would also stop shooting those lots of ammo and send those pictures to the ammo manufacturer. It has all the symptoms of over pressure.

[MoxyDave]

Check the headspace too. My guess is a tight chamber. 77gr rounds are a bit long and I bet some chambers have trouble with them.

[SINNER]

Check the headspace too. My guess is a tight chamber. 77gr rounds are a bit long and I bet some chambers have trouble with them.

I would agree with that if they were new rifles but they both have enough rounds thru to eliminate head space issues.

[gatordev]

Weird. I've only shot a couple other boxes from this case of ammo previously, but haven't had issues, nor heard any issues with CBC. But obviously something is wrong.

Thanks for the responses.

[Stone]

As mentioned above, OP on the blown primers. The scrapes can be from extraction but could also be at chambering. Brass is a fairly soft metal to begin with and that mark on the right side looks like a bolt lug scrape. Seems like there may be some extra resistance when chambering like bent feed lips or maybe a burr on the barrel extension feed ramp at the end of the ramp towards the inside. Did you use the same mag for both rifles? Who makes the mag you were using. Load up the mags or mag you where using with a box of the same ammo. Chamber and extract all the rounds without firing and inspect the brass and the bullets for tool marks. I would be suprised if both rifles were doing this unless the common denominator was the same magazine. Try this with both rifles and half of a fresh box for each.

[gatordev]

I definitely can't confirm it was both rifles. Unfortunately I didn't notice the problem until I was done shooting.

The mag was a really old straight PMAG 20 (Gen 1?) that was converted to a 10/20 mag. It doesn't even let the bolt lock back most of the time, regardless of rifle. I just keep it in my bag in case I need a 20 rounder for prone shooting.

I just started my hitch on days, so won't have a chance to mess with this for a week, but I'll have a look at this when I can.

[gatordev]

A small update...

Took out the rifle that was known to have at least one of the popped primers and scrapes and tested it again with a different mag (Pmag M3 w/ ~1500 rounds through it). Same problem. 2 out of 6 rounds fired had a popped primer. Tried with IMI M193 and no primer issues, but still getting scrapes on the brass.

Next range visit, I brought the same rifle and a completely new rifle (let's call it Rifle C). Shooting Federal M193 exclusively, problem rifle was getting scrapes on the brass, like before. I swapped out the complete BCG from Rifle C and tried it. The marking is significantly reduced. It looks like a small scratch on the very edge of the end of the brass, but I can't confirm it was on every piece of brass, even using the camera as a magnifying glass, because it was hard to see in person.

https://live.staticflickr.com/65535/48798729632_6514baa90e_h.jpg

I then put Rifle C's BCG back in Rifle C and shot it. ZERO marks on the brass, as normal. Rifle C (all parts) has 3500 rounds on it.

So seems like most of the problem is the bolt (extractor?) of the problem rifle? I'm not sure how to confirm if it's the extractor or the bolt itself except replacing the extractor. Or should I just not worry about it and mark up the brass that I don't re-use anyway? Bolt is a Colt bolt, for informational purposes.

Thoughts?

[Stone]

Is that pic from the "the rifle that was known to have at least one of the popped primers and scrapes"? Maybe its just the close up but that firing pin strike looks kind of deep. Keep it simple, take the bolt and firing pin(only) from the problem rifle out and put in a new set, not from rifle C. Run 3 mags(one being the ammo you suspect of being OP) of different ammo through it and see how it does. It seems like you have a few issues going on. If rifle C runs and functions well dont pull parts from it, keep it as is and it will be a known quantity of a functionig rifle, a base line, as long as those 3 different types of ammo run well through it. Lets rule out the ammo then go after the bolt/extractor/firing pin from the problem child.

[mustangfreek]

Or possibly and well known is the headspace might be a little short causing higher pressures

I had a mega barrel awhile back that did the same, checker it after and sure enough, tight ass chamber, that setup always showed brass with higher pressures.

Maybe , maybe not in your case. Just something I’ve noticed

[BoilerUp]

Where both bolt carriers of the same weight? Wouldn't a heavier bolt and buffer help slow extraction a bit and help with swipes?

[gatordev]

Is that pic from the "the rifle that was known to have at least one of the popped primers and scrapes"? Maybe its just the close up but that firing pin strike looks kind of deep. Keep it simple, take the bolt and firing pin(only) from the problem rifle out and put in a new set, not from rifle C. Run 3 mags(one being the ammo you suspect of being OP) of different ammo through it and see how it does. It seems like you have a few issues going on. If rifle C runs and functions well dont pull parts from it, keep it as is and it will be a known quantity of a functionig rifle, a base line, as long as those 3 different types of ammo run well through it. Lets rule out the ammo then go after the bolt/extractor/firing pin from the problem child.

I think the ammo problem has been solved. When I shoot the ammo, it pops primers. When I shoot anything other than the suspect ammo, it functions fine. Even with the suspect bolt, the suspect rifle shoots all other kinds of ammo without issues, other than the scraping. Ammo includes Fed M193, IMI 193, and even Silver Bear 55gr.

That picture is of the problem rifle with a known good BCG (different bolt and firing pin) than the original problem bolt and pin.

Rifle C, with it's known good parts is still whole and runs everything fine. I was only using its BCG as a test. That rifle won't be split apart.


Where both bolt carriers of the same weight? Wouldn't a heavier bolt and buffer help slow extraction a bit and help with swipes?

Same weight, or nearly so. Both are M16 BCGs. One was NiB (the good one) and the other is a standard finish Colt. I haven't tried messing with the buffers, but I believe the problem rifle has a H2 in it. I'll have to check.

I have no way to check headspace, unfortunately.

[cjd3]

I have no way to check headspace, unfortunately.

I have a set of .223 Go No Go Guages you can borrow. Let me know if you are interested. I have no need for them in immediate future, so if anyone else wants to borrow them, lemme know.

[Stone]

Definetly wont hurt to check headspace, If you can borrow them from CJ.(very generous offer BTW!) Yeah you got a batch of bad ammo which could also have some overly soft brass. I would set that stuff aside now since its a known issue. I would take the problem child and give her a full strip down and cleaning. Get into the extractor claw, the bolt face and the barrel extension with your dental pics and Q-tips as you may have excessive brass shavings everywhere impeding performance. Check down in the trigger well to for popped primers. Give it a solid lube job, I run my rifles wet and they seem to do very well. Load up a mag or two of some good ammo and see how it does. Keep an eye on its extraction to at this point as well. If you still have the heavy scrape marks just swap out the bolt with a new one and see how it functions. Hopefully this will narrow it down to a specific point... This all goes to show how important it is to inspect your spent shells once in a while...

ETA: When your stripping it down or putting it back together, look over everything real well. Sometimes we forget that stripping down and cleaning a rifle is always the best oportunity to inpect parts for excessive wear and not just a time for cleaning. Myself included...[BD]

[gatordev]

I have a set of .223 Go No Go Guages you can borrow. Let me know if you are interested. I have no need for them in immediate future, so if anyone else wants to borrow them, lemme know.

I really appreciate that. Does it matter if it's a 5.56 chamber? I can't remember if a .223 gauge is compatible, but it seems like it would be.


Definetly wont hurt to check headspace, If you can borrow them from CJ.(very generous offer BTW!) Yeah you got a batch of bad ammo which could also have some overly soft brass. I would set that stuff aside now since its a known issue. I would take the problem child and give her a full strip down and cleaning. Get into the extractor claw, the bolt face and the barrel extension with your dental pics and Q-tips as you may have excessive brass shavings everywhere impeding performance. Check down in the trigger well to for popped primers. Give it a solid lube job, I run my rifles wet and they seem to do very well. Load up a mag or two of some good ammo and see how it does. Keep an eye on its extraction to at this point as well. If you still have the heavy scrape marks just swap out the bolt with a new one and see how it functions. Hopefully this will narrow it down to a specific point... This all goes to show how important it is to inspect your spent shells once in a while...

ETA: When your stripping it down or putting it back together, look over everything real well. Sometimes we forget that stripping down and cleaning a rifle is always the best oportunity to inpect parts for excessive wear and not just a time for cleaning. Myself included...[BD]

All good stuff. Unfortunately I've done 95% of that. I've broken down the bolt and scraped out the extractor and nothing found there. There was a tiny bit of brass in the extractor pocket, but not in a place to impede movement. Lower had no primers. The only thing I didn't do was hit the barrel extension with a dental pick...that's easy to go do. Otherwise it was cleaned as well. My last post "update" post with the picture was after all of that. As I said, bolt was swapped out with positive results. I think at this point, it's time to track down a spare extractor and headspace (for good measure).

Or just shoot the damn thing, because it functions fine, otherwise.

[cjd3]

From my research, the headspace is the same. For the helluvit, I’m checking headspace today since I have nothing better to do.

Also, your inbox is full.

[gatordev]

From my research, the headspace is the same. For the helluvit, I’m checking headspace today since I have nothing better to do.

Also, your inbox is full.

I think I cleared some PMs out for it to work now.

[mustangfreek]

To get an accurate reading on a 556 chamber, you would need a set of 556 guages.

223 rem guages of certain brands are on the longer end of the spectrum. So closer to 556.

The throat s just a hair longer, as why most times 223 rem in a 556 chamber is no problem, it’s the 556 cases that are a smidge longer, have the notes somewhere in my reloading notes.

[gatordev]

To get an accurate reading on a 556 chamber, you would need a set of 556 guages.


From my research, I believe you are referring to a throat gauge. Like cjd said, according to the internet (and yes, I take it with a grain of salt), a Go/No-GO/Field gauge is the same for .223 and 5.56. But I welcome evidence to the contrary.

[alamo5000]

Gator,

Watch this video if you want. 12 minutes or so about the difference between 223 and 556.

https://youtu.be/VCS4fXFmCyA

[alamo5000]

Based on that video and the fact that you were shooting heavy bullets for caliber it leads me to think this is probably the most likely cause.

Meaning that chamber might be one of the hybrid type and you were definitely shooting 5.56 brass so the added few thousands on the brass plus the heavy bullet probably caused your problem.

Throw in the chamber dimension and that solves it in my mind.

[gatordev]

Based on that video and the fact that you were shooting heavy bullets for caliber it leads me to think this is probably the most likely cause.

Meaning that chamber might be one of the hybrid type and you were definitely shooting 5.56 brass so the added few thousands on the brass plus the heavy bullet probably caused your problem.

Throw in the chamber dimension and that solves it in my mind.

Can you be a little more specific about what it is you're talking about? Which problem do you think is solved, in your mind?

The barrel is a 5.56 barrel (V7) and the scraping issue happens regardless of bullet type (length/weight), but not universally (different bolt, no scraping).

[alamo5000]

I started with the biggest problem first. Popping primers is not good. Its definitely not safe so that's where I began then I worked backwards.

Basically to me where I would start looking is at the chamber of that specific barrel. It would explain a lot if someone can look at it and measure etc.

If you watch that video he goes into some of the different length and whatnot measurements of 5.56. If you add all that up and then throw in a larger bullet with a different Ogive it can easily explain why that ammo works in one gun but pops primers in that one. Basically that all boils down to the chamber and/or throat dimensions are tight for that manufacturer (or on that given day that it was made or whatever).

My theory is that the chamber is too tight and all the tolerance stacking from the barrel itself to possibly the brass and bullet combination is leading to a dangerous situation. Little things like the bolt tolerances or the wear on the carrier or gas rings become amplified in importance. Basically it sounds like that rifle is operating at the top edge of 'safe' and it is most likely how they reamed the chamber and whatnot.

That would also explain why you not only blew primers but also are getting swipe marks on all your brass. Those swipes no matter how big or small are from pressure so those swipes plus the blown primers they keep on leading me back to the whole chamber tolerances thing. The bolt might be a thousandth here or there but still within tolerance. If the chamber is overly tight it makes that window of tolerances for the bolt razor thin.

If you can shoot that same ammo out of another rifle without cratering or blowing the primers (especially on crimped 5.56 brass) then that to me has to be it. It would explain the swipe marks across the board too.

I would probably wager you a beer on it. If you take it to someone that has the ability to measure and examine that-- if I am wrong I will buy you a beer of your choice.

[alamo5000]

Can you be a little more specific about what it is you're talking about? Which problem do you think is solved, in your mind?

The barrel is a 5.56 barrel (V7) and the scraping issue happens regardless of bullet type (length/weight), but not universally (different bolt, no scraping).

Also sorry for the first response. I typed it on my phone so I wasn't clear.

[mustangfreek]

From my research, I believe you are referring to a throat gauge. Like cjd said, according to the internet (and yes, I take it with a grain of salt), a Go/No-GO/Field gauge is the same for .223 and 5.56. But I welcome evidence to the contrary.


Yes the 556 has a longer throat /freebore

Well if our just roughly checking, the 223 guages might help. As a lot of times 223 go guages are roughly the same, it’s the 556 no go guage that’s longer then the 223 guages. so in some instances a 223 no go will close on a 556 chamber, which tells ya...not much...lol.

Again if just wanted to make sure it’s ok, a colt field guage will let ya know. But your instance sounds tight..

Of course theirs other ways to figure out exactly your chamber dimensions, just need a few tools

Found this pic referring to the differences in guages

[gatordev]

Alamo, I get what you're saying, and it's possible that, at the end of the day, that is part of the issue. But...



If you can shoot that same ammo out of another rifle without cratering or blowing the primers (especially on crimped 5.56 brass) then that to me has to be it.


That's not what's happening. As I've mentioned, the ammo popped primers out of two different rifles and the "problem" rifle isn't popping primers on other 5.56 brass.


If you add all that up and then throw in a larger bullet with a different Ogive it can easily explain why that ammo works in one gun but pops primers in that one.

Again, that's not exactly what's happening. It shoots other 77gr 5.56 fine.

I can see where the tolerance stacking may come into play, since with a different bolt, the scraping goes away. I think another thing I need to try is put the "problem" bolt in Rifle C (known good rifle) just to see what happens, since Rifle C's bolt worked fine in the "problem" rifle.

As always, it's a matter of having the time to mess with all this stuff.

[cjd3]

I just found this. Headspace Gauge and the AR (https://www.arbuildjunkie.com/headspace-gauge-ar/).

[Joelski]

Coinkydink.

[gatordev]

Yes the 556 has a longer throat /freebore

Well if our just roughly checking, the 223 guages might help. As a lot of times 223 go guages are roughly the same, it’s the 556 no go guage that’s longer then the 223 guages. so in some instances a 223 no go will close on a 556 chamber, which tells ya...not much...lol.


My apologies, Mustang. I did some more reading last night and found some more info that goes right along with what you're saying (and now cjd's link above). Thanks for pointing it out and making me dig deeper.


I just found this. Headspace Gauge and the AR.

That's good stuff. I think I'll give your gauges a try and see where it stands, but grab some 5.56 gauges to have. I should have bought them a long time ago, but they were always out of stock.

We'll see what they all say when I play some more with the rifle.

[gatordev]

So an update... Learned some stuff in the process, but in the end, I'm not really sure I've "solved" anything. And I'm not certain there's anything to solve.

A recap...the players:

"Problem Rifle": Makes marks on spent, ejected brass. Does NOT make marks on unfired brass.

"Rifle C": Known good rifle, used for testing. Shoots everything fine with no issues.

Update:

- The Problem Rifle was checked for headspace with 5.56 gauges. Bolt closed on Go-gage...PASS. Bolt would not close on No-Go gauge...PASS.
- Problem Rifle BCG was put in Rifle C and worked 4.0, no brass marking (this had me puzzled after it passed the headspace test).
- Rifle C BCG put in Problem rifle and worked 4.0, no brass marking.

Conclusion: I have no idea. At this point I can't find anything wrong with the Problem Rifle. I can swap out the extractor, but it didn't make marks when put in another rifle. Unless someone has other ideas, I'm at the point where I'll just keep an eye on it but keep shooting.

[Stone]

I would say you solved 98% of the problem when you took the over pressured ammo out of the equation. When fired, the brass expands to seal the chamber and with the ammo being OP it delayed the extraction window by just enough that the extractor had to have a death grip on the case to get it out. I’m actually surprised it did but that would explain the death grip marks on the spent casings. Just because the primers didn’t blow out on all off them, doesn’t mean that the rest of the cases from that lot were not over pressured as well. Hence the death grip marks on the other cases. With that said you may have knocked down that sharp edge on the extractor which may explain why you’re still getting some marks. A sharp or new extractor claw will fit nicely around the case and in most instances you won’t even know it was there after ejection. I would take that extractor out and throw it as far as you can and put in a new one. Also, with it having such a death grip on it you may have too much spring pressure. Put in a new extractor spring and O ring as well then test fire it. If you still get marks take the O ring out and fire a mag with just the new spring. If you’re not happy with the results it sounds like switching complete BCG’s from the PR with rifle “C” was a fix as well but I would still toss that extractor. Sometimes these problems seem like a PIA but this is the stuff that keeps us frosty and most of all “learning has occurred”

[mustangfreek]

Huh

Sounds like that ammo is just on the hot side..I have some reloads in 77 gr that are deadly accurate but swipes and flattened primers are the norm from it

Also was gonna say, maybe try a different extractor and it spring/insert. I keep a few bcm kits on hand and never had a problem with them

But I’d just shoot it some more and just keep an eye on it

[gatordev]

A new extractor it is. I had one Colt spare, but grabbed a second, so I can still have a spare after swapping this out.

Interestingly, regardless of ammo, it was making the marks both with and without the o-ring. It actually wasn't running an o-ring originally (didn't realize the bolt didn't have one), so way back when I was testing this stuff, I put one in. No change on the marks.


Sounds like that ammo is just on the hot side..

But the thing to keep in mind is that it makes the marks with ALL ammo. That's what really had me scratching my head. But like you said, I'll shoot it and keep an eye on it.

[gatordev]

Closing this out, as I've ceased caring after the last test...

Tried a brand new extractor with new gold Colt extractor spring. Still marking the brass. It looks like the ejector may be marking one side and the extractor marking the other. Otherwise it continues to function fine. I'll just keep shooting it.

I also tested the popped primer ammo in two other rifles and no issues. Perhaps what Alamo mentioned about chamber tightness makes this gun not like that ammo. Whatevs, it shoots everything else fine, so I'm moving on.

[Stone]

Like you said, if all the function is there, drive on...