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PostPosted: Tue Nov 07, 2017 9:12 pm 
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So, I was cleaning up the guns after this past weekend’s session and noticed an interesting wear issue on one of my 5.56 bolts that I’ve never seen before. There’s a little bulge/ridge on the neck where it goes into the carrier:

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...but no discernable matching “dent” on the inside (sorry no internal pics turned out). In this pic it almost looks like the NibX coating boiled up and formed a ridge of molten metal, then cooled:

Image

I’m taking it out of service regardless, but any thoughts from the hive mind?

This bolt only has a couple hundred rounds through it, almost all 300BLK...though most were suppressed, so it’s feasible that there could have been some pressure spikes.

Tempted to send it back to PSA for a look, but since I bought it on sale several months ago don’t know if they’d consider a warranty replacement.

I guess it never hurts to ask though...

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PostPosted: Tue Nov 07, 2017 10:23 pm 
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I'm no expert, but it looks like carbon to me.

I never cleaned my AK74 and it got some reallll nasty stuff on it that looked like metal.... I hit it with a dental pick and penetrating oil and some wire brushing. Took about an hour to get rid of about a square-inch worth.

Try scraping it off and see what happens (without ruining your metal finish)

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PostPosted: Tue Nov 07, 2017 11:11 pm 
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Should be able to scrape it right off with a dental pick or even the firing pin. If you can't let us know.

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PostPosted: Tue Nov 07, 2017 11:27 pm 
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I'm on the same page as Sterticus and JeeperCreeper.
Back when ARs were expensive got a (for the time) very good deal on a used AR. The bolt looked like yours but much worse, because it was carbon-tastic due to the rifle having had a bunch of Wolf ammo (works, but it is dirty) through it. I left it in a bowl of Hoppe's Number 9 for a few days and what didn't just melt off due to the miracle of chemistry was easily scraped off with a dental pick.
With that said, if a good cleaning doesn't do the job don't be shy about replacing the bolt. Your health is awfully valuable when you think about it.

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PostPosted: Tue Nov 07, 2017 11:40 pm 
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Thanks y’all... I should have mentioned that this is after a few minutes in the ultrasonic cleaner and after a scrub down with a brass brush and some Hoppe’s #9. It looks like it has a copperish tint...but that could be from the brush I suppose.

Regardless, I’ll put it in to soak with the guts from my AAC .22 can (and the entire Radical .22 can that won’t come apart :vmad: ) that’s soaking in a tub of Hoppe’s out on the work bench, and see if it comes off mañana.

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PostPosted: Wed Nov 08, 2017 2:14 pm 
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I'm no expert, I originally thought what everyone else did. However that last pic it really does look like some sort of melt/weld. It looks like a really crappy weld job. Seeing that you cleaned it with an ultrasonic I would believe that maybe a pressure spike of hot gas may have scorched it. not sure how that would happen, I'd assume your gas tube would look similar on the inside.

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PostPosted: Wed Nov 08, 2017 4:53 pm 
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I'm not familiar with the stuck carbon issue, but it also looks like it could be some kind of severe fretting wear. The build-up of material and surface finish would be somewhat consistent with severe fretting, but I wouldn't expect it to occur is so few cycles, unless the loads were really high, and then you might expect more displaced metal nearby anyway. Maybe some foreign object got jammed in there? You said that you'd already inspected the inside, but I would double-check that there isn't a matching wear pattern on the mating part, which might suggest the carrier should be taken out of service as well. :-/

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PostPosted: Wed Nov 08, 2017 8:03 pm 
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Thanks again everyone... just home from work and pulled the bolt out of the Hoppe’s soup, and went over it with a BONE tool.

Guess what?

Image

Interesting... Looks like it was mostly, if not all carbon after all, but there’s a definite wear mark where that ridge (pile?) of carbon was sitting. Feels smooth, but it’s definitely missing some of the coating or at least changed color in that area.

Is it possible the carbon built up there and simply trapped enough heat to discolor the bolt?

I’ll see if I can find a microscope (one of my neighbors is a college biophysicist professor) or at least a better magnifying glass to see if there’s any actual wear.

I did run a very fine pick down the inside of the bolt and looked very closely inside the carrier for any marks, dents or wear spots and couldn’t find anything there.

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... A defensive gun without training is basically a talisman. It might ward off evil, but I wouldn't count on it.


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