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  1. #1
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    Brass marking on extraction (and blown primers)

    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):



    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.

  2. #2
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    That ammo is over pressured. Ejector/extractor marks on the head of the case are indications of slight overpressure. Blown primers are severe overpressure.

  3. #3
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    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.

  4. #4
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    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.

  5. #5
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    Quote Originally Posted by MoxyDave View Post
    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.

  6. #6
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    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.

  7. #7
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    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.
    Last edited by Stone; 12 September 2019 at 08:29.
    The best way to survive a violent encounter is to be the one inflicting the most violence.

  8. #8
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    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.

  9. #9
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    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.



    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?

  10. #10
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    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.
    Last edited by Stone; 26 September 2019 at 12:35.
    The best way to survive a violent encounter is to be the one inflicting the most violence.

  11. #11
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    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

  12. #12
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    Where both bolt carriers of the same weight? Wouldn't a heavier bolt and buffer help slow extraction a bit and help with swipes?

  13. #13
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    Quote Originally Posted by Stone View Post
    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.

    Quote Originally Posted by BoilerUp View Post
    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.

  14. #14
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    Quote Originally Posted by gatordev View Post
    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.

  15. #15
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    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...
    Last edited by Stone; 26 September 2019 at 21:01.
    The best way to survive a violent encounter is to be the one inflicting the most violence.

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