Mysterious Marks on Bolt Lugs - Page 1

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[ARCHIVED THREAD] - Mysterious Marks on Bolt Lugs

Posted: 5/26/2017 10:36:18 AM EDT

Brand new 300 BLk build. 30 rounds of test firing a mix of ammo brands and weights showed no unusual wear and no malfunctions. Sold to an inexperienced friend who put 100 rounds or so through it and reported failure to eject at least twice per mag. I took a look at it and immediately noticed unusual markings and bulging on the bolt lugs. Also, the pin for the extractor was slightly bent. Weird. Put a new bolt in the BCG and we're back to flawless operation, but with a new twist... Now I'm getting an unintentional "double tap" like a bump fire about two or thee times per mag.
Not sure if these two issues could be in any way related. I'm mostly concerned with the marring and disformity on these bolt lugs. They should be flat and clean with square edges. There is bulging and almost a ramp-type appearance to the profile on several of the lugs. The marking and bulging is on the rear facing edges of the lugs.

Any ideas???????

I will certainly try to re-inspect the new bolt after a few more rounds.

Posted: 5/26/2017 10:38:31 AM EDT

[#1]

No pics, no care.

Posted: 5/26/2017 10:41:25 AM EDT

[#2]

Is it headspacing/ locking up correctly? Is he using reloads/wrong primers? Is the firing pin fucky? What's the spent brass look like?

Posted: 5/26/2017 10:47:22 AM EDT

[#3]

You gotta post pics if you want advice like this. Learn.

Posted: 5/26/2017 10:48:00 AM EDT

[#4]

Quote History

Quoted:
No pics, no care.

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Posted: 5/26/2017 10:54:57 AM EDT

[#5]

Adjustable gas block?

Posted: 5/26/2017 10:56:49 AM EDT

[#6]

Quote History

Quoted:
No pics, no care.

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This

Posted: 5/26/2017 10:57:57 AM EDT

[#7]

You and your buddy sound like wizards.

Posted: 5/26/2017 12:22:47 PM EDT

[#8]

Everybody a little testy this morning? I'm new to AR15.com, not to AR-15s. Apparently you can't just simply attach an image.
I have terrible internet. Here's the first of two pics. Tried to use a free image hosting service on line for the URL. We'll see if it works.

<a href="https://ibb.co/dAuwJF"><img src="https://preview.ibb.co/iRFQCa/3.png" alt="3" border="0"></a>

Posted: 5/26/2017 12:33:06 PM EDT

[#9]

I'd say there is something very fucky with that barrel extension and bolt, but who knows? - not enough info.

Posted: 5/26/2017 12:34:02 PM EDT

[#10]

Everything else is completely normal.
And like I said, it worked fine at first, no marring. And it worked fine after the bolt replacement. Not sure what the other guy did in the mean time. That's the mystery.
16" 300 AAC barrel from BCA. Carbine length gas, .125" gas hole, normal gas block, proper alignment, proper headspace, lock-up, spent brass and primers look fine.

My second pic won't upload

Posted: 5/26/2017 12:37:26 PM EDT

[#11]

Whatever torqued up the bolt also put a lot of stress on the upper and may have forced it out of spec.

The 100 rounds he fired...any reloads?

Posted: 5/26/2017 12:40:01 PM EDT

[#12]

Posted: 5/26/2017 12:41:12 PM EDT

[#13]

That bolt is made of playdough ... or someone is about to blow up a gun.

Posted: 5/26/2017 6:15:42 PM EDT

[#14]

What brand bolt is that?

Is he shooting reloads using 308 powder charges?

Posted: 5/26/2017 6:19:46 PM EDT

[#15]

Quote History

Quoted:
That bolt is made of playdough ... or someone is about to blow up a gun.

View Quote

Yep.

Posted: 5/26/2017 6:30:38 PM EDT

[#16]

Not saying that it's possible but it looks like it unlocked late after being subjected to over pressure rounds. Either that or that bolt is super soft but you would expect to see a different type of damage to the bolt.

What rounds was he shooting?

Posted: 5/26/2017 6:35:34 PM EDT

[#17]

Soft bolt.

Posted: 5/26/2017 6:36:58 PM EDT

[#18]

Squishy squishy

Posted: 5/26/2017 6:38:56 PM EDT

[#19]

...and the headspace will rapidly lengthen = bad.

Posted: 5/26/2017 6:43:29 PM EDT

[#20]

Quote History

Quoted:
Soft bolt.

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this.

also looks like it's made from Chinese 1018.

Posted: 5/26/2017 6:46:40 PM EDT

[#21]

Looks like chinesium

Posted: 5/26/2017 6:48:30 PM EDT

[#22]

Mushrooming with no cracks usually means too soft as others have said.

Posted: 5/26/2017 6:50:31 PM EDT

[#23]

Quote History

Quoted:
Looks like chinesium

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And she won't chooch.

Posted: 5/26/2017 7:32:18 PM EDT

[#24]

Throw my vote in for bad reloads if they are reloads

Posted: 5/26/2017 7:40:43 PM EDT

[#25]

chineseum won't chooch, lol

who made the bolt,

Posted: 5/26/2017 7:53:31 PM EDT

[#26]

Wayyyyyy too soft of a bolt. Might need a new barrel if the bolt buggered up the extension. Guarantee you headspace got way out of spec as that bolt smooshed. You're probably not far from a case head separation.

Brand name parts with a solid reputation cost more to pay for things like QC that keeps their reputations solid.

Double taps could be from the firing pin getting trapped forward in the bolt head plus excessive firing pin protrusion due to bolt smoosh.

Lucky to keep all your fingers with that quality build!

Posted: 5/26/2017 7:58:39 PM EDT

[#27]

Who is the manufacturer of the bolt

Posted: 5/28/2017 3:33:32 PM EDT

[#28]

@TAC_75972

Update?

Posted: 5/28/2017 3:38:34 PM EDT

[#29]

Quote History

Quoted:
Mushrooming with no cracks usually means too soft as others have said.

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This. What brand bolt is that?

Posted: 5/31/2017 4:03:27 PM EDT

[#30]

what brand BCG is that?

AR Stoner? I remember some problems with them in the past.

Posted: 5/31/2017 4:08:47 PM EDT

[#31]

Bad steel or bad heat treat. or both

Posted: 6/2/2017 12:03:13 AM EDT

[#32]

It was a PSA bolt. No problems after replacing bolt. No reloads, just regular store bought Rem white/green box as far as I know. I cannot say for sure what was done with the gun while not under my supervision. Hence the mystery. I am wondering if they could have improperly assembled the gun after cleaning that may have resulted in this damage. I wonder what would happen if you fired ONE shot with... let's say... the cam pin missing... and then you realized something was wrong... put the pin back in and brought it back to the guy you bought it from with a boogered up bolt and bent extractor pin. This is the direction I am thinking, because everything was good quality and good assembly and no reloads. So... what could this novice have done to cause this? Again.... high quality barrel and upper receiver from BCA and BCG from PSA. Same exact components I've put together many times. No problems with over 30 rounds of test firing before the gun left my sight. No problems after replacing the bolt. So what happened in the mean time? I can't wait to inspect the new bolt after some use, but it will be several days before I get the opportunity. I may ask him to send me pics if I can get cooperation.

Posted: 6/2/2017 12:13:22 AM EDT

[#33]

Yikes. Danger, Will Robinson. If no cam pin and one managed to fire = kaboom. Is this person such a retard to try such a thing?

Send that bolt back if possible to mfr. If all else is good, maybe no heat treat for that bolt? Did you check head space, and measure fired brass with the new bolt? Inspect extension?

ETA if he did something like that, then you don't want to be on the hook for anything with this guy. If the gun checks out, give it back, tell him he's on his own and good luck.

Posted: 6/2/2017 12:19:48 AM EDT

[#34]

Deformity, not disformity.

I'm thinking the bulging is due to the doubling and that the second shot is fired before the bolt fully locks up.

Posted: 6/2/2017 12:36:44 AM EDT

[#35]

Quote History

Quoted:
It was a PSA bolt. No problems after replacing bolt...everything was good quality

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View All Quotes

Quote History

Quoted:
It was a PSA bolt. No problems after replacing bolt...everything was good quality

I don't think that phrase means what you think it means.

Quoted:
I am wondering if they could have improperly assembled the gun after cleaning that may have resulted in this damage. I wonder what would happen if you fired ONE shot with... let's say... the cam pin missing... and then you realized something was wrong... put the pin back in and brought it back to the guy you bought it from with a boogered up bolt and bent extractor pin.

No missing parts changes the forces acting on the bolt lugs. That is solely from the round fired.

A missing cam pin would mean the bolt would not be limited to it's normal travel and would likely foul up the gun before it chambered a round. If it somehow chambered a round there would be nothing to cause the bolt to rotate into battery and because the carrier could advance forward too far you'd either get a slam fire or the rifle would fire without the bolt locked up which would destroy the rifle (but not damage the lugs the way they were).

The thing that caused your buddy's problem was that the bolt was made out of unhardened steel (like never made it into the heat treat oven at all) and deformed from the forces exerted on the bolt lugs by firing. That's caused by shitty QC which is how you keep the price down.

[ARCHIVED THREAD] - Mysterious Marks on Bolt Lugs

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