Mystery spiral on 223 bullet?

[Tesoro]

I have a 223 AR with WOA match bbl. I was shooting some loads the other day and had to eject a loaded round. I took a close up look at it just for the heck and noticed something unusual. On the flat part of the bullet behind the ogive were 3 evenly spaced radial lines. It was actually one line that started towards to the tip and made nearly 3 revolutions to the rear. I took a pic of it attached but darn bullet so shiny hard to get a good one.
I am curious as to what caused this and either I am being stupid or just cant figure it out. I understand how an ar functions pretty well. the guy next to me was ex military and leo and said those are rifling marks. I said no for 2 reasons one being the bolt only turns about 15deg to lock up and the marks are a spiral. Plus I have my oal set up right and this bullet was .010 off the lands.
When I got home i took a nosler factory load which was .35 off lands in my barrel and chambered/ejected it. It also got this spiral but only one and a half spirals. The scratches are light but deep enough to barely feel with your fingernail.

I am curious and its driving my nuts! How can a cartridge spin to make those marks?

 

[Pdvdh]

Can't see any spiral in the picture...

 

[Tesoro]

magnify the pic. can see 2 parallel looking lines on the bullet. the third one didnt show up on the pic

 

[Dosh]

Is the chamber clean?

 

[Pdvdh]

Blacken the bullet with permanent felt pen. Chamber again. Search for spiral.

I don't believe that spiral is possible from the 15* rotation of the AR15 action.

Unless you can duplicate on the blackened bullet chambering, look elsewhere.

 

[Pdvdh]

The only way to get those rings is if the throat in your chamber has rough reamer ridges in it. That means whoever cut the chamber did a poor inspection of the work.

Maybe a defective reamer. Or a defective operator...

 

[Tesoro]

Thanks for inputs.
Chamber spotless the bullet aint close to the lands. I know how to do that stuff. The mystery is the spiral groove that could only be formed by the bullet rubbing on something while it does a 360 to 720+ spin! I looked upsome super slow mo videos on injection in an ar and no spin.
I have a woa match bbl n even if there was a burr in the throat then it would be a horizontal or diagonal streak not a spiral.
I dunno!! More curiosity as its a miniscule scratch that wont affect accuracy after the bullet burns its way out over 6 lands. But I wont sleep well till I figure it out hah!

 

[Pdvdh]

There's only about 4 possibilities.
1) seater stem with raised spiral ridges imprinting during seating,
2) chamber throat/taper with raised spiral ridges imprinting bullet jacket when cartridge is slammed home,
3) bullets came with markings from the factory,
4) magic.

 

[Tesoro]

There's only about 4 possibilities.
1) seater stem with raised spiral ridges imprinting during seating,
2) chamber throat/taper with raised spiral ridges imprinting bullet jacket when cartridge is slammed home,
3) bullets came with markings from the factory,
4) magic.

1) not possible due to location of spiral
2)only possibility - will borescope I dont have a good one.
3)no
4) dont believe in magic!

 

[Pdvdh]

Ridges in the throat is about all that's left, now that you've eliminated the other two.

The imprint should be identical on each bullet slammed home, provided each bullet is seated to the same depth.

One way to test further without a bore scope is to seat the bullets more deeply. The imprinting will become faint, or disappear entirely. Provided the bullets aren't moving in the case neck during chambering slap.

No way are the spiral markings due to cartridge rotation during chambering.

 

[Tesoro]

Well I think I got to the bottom of this 'mystery'! This am I called WOA and got speak to the man himself - John Holliger.
He said that those spirals are not uncommon to see and have to be caused by an unexplained spin to the cartridge with contact in the chamber during the violent chambering process. He said that the cartridge is already on its way into the chamber before the bolt catches up with it. ie when the bolt slams into a cartridge and strips it off the mag it actually pops it forward and then catches up with it to slam it into place. Somewhere during the nano second of free flight the cartridge can spin as evidenced by the spiral lines on bullets. This makes sense to me. I wonder if maybe the spring pressure exerted on one side of the cartridge in the mag before it is stripped causes this?

Also he said that if there was a 'burr' in the throat then the rifle flat out wouldnt shoot and you would know it.

I will bet that if you soft load a round off a mag and push it into place and then eject it you wont see any spiral marks. But if you slam it into place then you would/could get the spirals like I experienced. I also noticed that there were more spirals (more spin) on a cartridge loaded by firing than by releasing the bolt catch. ie the bolt slams home harder during firing than by manual release and somehow imparts more spin.

if I could have taken a better pic of the evenly spaced 3 line spiral scratch on the bullet you all could have appreciated it better...could only be caused by the bullet rubbing on something and making 3 spins as it passed by it.


This is some pretty nit picky stuff here but hey when I see some weird mark on my rifle mechanics or cartridge I want to know what caused it!! live n learn. No magic!

 

[Pdvdh]

Interesting.
My AR doesn't spin the cartridge like that at all. My opinion is that yours doesn't either. I'll explain the basis for my position. I'm on no mission to make my conclusions your conclusions.

Within the past 12 months I've worked on my AR several times. I examined my fired cases, and also examined unfired cartridges that had been chambered.
The first corrective measure I took was in response to noting that the bottom front of my bolt was cutting a scratch into the top shell casing left in the mag while ramming the cartridges home into the chamber. So I rounded and polished the sharp leading edge from the bottom of the bolt and that cured the scarring of the sidewalls of the cases.

Later I noticed a spiral scratch on my bullets when I extracted a live round from the chamber. The spiral scar was similar to the twist on a barber shop post or a candy cane. An elongated spiral, with about 10-15 degrees of rotation. Investigation determined this was being caused by the bolt lug recesses in both of the two feed slots in the breech. The scars were substantial, cutting a sharp spiral with a raised lip. Enough to affect bullet BC and perhaps accuracy. So I used a Dremel hone to round off the sharp 90* edges and that eliminated 95% of the depth of these scratches.

The point being, my cartridges were not rotating more than ~ 15*, based on the scratch pattern the bolt lug recesses left on my bullets. I also researched the bullet scratching I saw on my bullets and learned this was fairly common. Never once did I read of cartridges being rotated even 90*, let alone 720* or more. Yours aren't either, in my opinion.

The angle of the spiral scratch on my bullets was less than the angle of the cam pin slot cut into the bolt. So a bit less than 15*, in my estimation. The scars left on the bullets were about 1/3" long. 10-15 degree rotation. Identical to the photos others posted showing bolt lug recess scars on their bullets.

I doubt your cartridges are being rotated 1-2 revolutions by the bolt slamming them home. I'd have to it on high speed photography to believe otherwise.

If you Google research this, I don't think you'll find evidence of multiple cartridge revolutions during chambering. I know I didn't. And I used search terms that should have snagged some hits.

 

[Tesoro]

I hear ya but what you are describing are all common scars/solutions from extraction damages and not insertion. But when an old pro tells me something I listen. I didnt find anything via google either so thats why I called him up and he had my answer right away without having to think about it. fact is the only way my scratch could have been made was for the bullet to rotate nearly 3 times and that cant happen on extraction so has to be on insertion! Unfortunately I dont think a video could be taken to prove that a case temporarily pops forward of the bolt after being freed from the magazine and spins. However the bullet markings sort of prove it because there is no other plausible explanation. I also have pretty tight chambers in my uppers so maybe the markings are amplified in my case.
Moral of story is better you understand how your gas gun works the better for you and shooting/reloading!

 

[Pdvdh]

I hear ya but what you are describing are all common scars/solutions from extraction damages and not insertion.

Perhaps you meant to type something otherwise? For the record, both of my issues were related to the feeding of rounds into the chamber. The scars were identified before the bolt was thrust backward under recoil.

The scarring on my cartridge cases remaining in the top of the magazine was present and visible when I dropped the mag after manually letting the bolt ram home. The bolt had never yet moved rearward during the ejection cycle. I initially saw the scarring on some cases ejected under fire, which is what led me to investigate in the first place. To eliminate the scratch on the body of the cases, I removed some sharp edges from the forward-most, underside of the bolt, the location which would rub along the length of the underlying cartridge case while stripping and feeding the top round out of the in the mag and ramming it home into the chamber. This cured the case scarring.

The spiral scar on my bullets was observed after slow, manual extraction of the live rounds from the chamber. These rounds never experienced an extraction cycle and of course they can't, as they depart the front of the barrel at 3000fps prior to the extraction cycle. I cleaned off the feed ramp bolt lug recesses and observed the jacket-colored residue on both of the two feed ramp bolt lug recesses in the lower breech of the barrel, after letting a few loaded rounds ram home into the chamber. I rounded and polished the 90* angles and the bullet scarring problem was cured.

Your source of information on the cause of the tight spiral scarring is the manufacturer of the barrel, correct?

I just find it difficult to accept that you're the first AR15 owner to observe tight rotational spirals on your bullets if this occurs with any frequency. If it was common, and the cause was also commonly known, we'd find it on a Forum, somewhere or another. Multiple cartridge rotations while the cartridge is slammed forward 4"... If no one else is posting about this, it must be quite rare. Obsessive-compulsive disorder is more common among AR15 owners than owners of other firearms, in my experience... I have a touch of it myself.

My cartridges rotate during feeding at a slow rate, based on the my bullet scar patterns. My scar pattern is identical to that reported by many other AR15 owners. Candy cane rate of rotation over length of the scar on my jackets.

If you seat your bullets 0.025" deeper, the spiral pattern might diminish or disappear. An easy test to the barrel manufacturer's theory. If the spiral is caused by 720* or greater cartridge rotation, it'll likely still be there. On the other hand, if there are any raised ridges in the throat that could imprint on the bullets, seating them deeper in the cases should reduce that imprint. A no-cost test. A good quality bore scope would also resolve the presence or absence of ridges imprinting on the the bullet surface near the ogive. But they're expensive, unless your buddy has one.

Of course, if your rifle shoots well and doesn't copper foul excessively, there's really no harm worth correcting.

The scars on my bullets were substantial. Same with my cases.