Odd 'step' in the bore?

[ssgross]

I'll take a stab.
Warning: Cheaper bore cams can be misleading. I have a teslong, which can film birds-eye like yours as well as sideways. If you want to talk someone down in price...show them the Birdseye of the rifle they are selling. It always looks like crap. The reason is due to the reflective properties of the metal surface. After firing, no matter how much you clean, all of the metals microscopic 'imperfections' are going in the same direction. Makes even a new barrel look dull grey, perhaps even frosty (note I said microscopic. happens even on a brand new barrel after hand-lapping), whereas the side-view will show perfect, bright, and shiny.

I'm not saying you are wrong, just advising to double check. To double check without buying an expensive camera -- I would simply slug the bore. Before tapping my slug in, I would mark my driving rod for where to expect the flaw, and carefully note any difference in the force required to tap it through the area. Next, I would perform a straightness test. This involves dropping an index pin of a certain diameter and length down the bore. If it's in spec, it will fall all the way through with no resistance. Someone with a bigger library than me can pull up the spec for your rifle.

EDIT: here you go...https://pacifictoolandgauge.com/bore...lerances_-_001
and https://feeds.brownells.com/userdocs/learn/Inst-478.pdf

Some other general but related things about bore pictures I have noticed in the past:
It could be an illusion. I've heard first hand from someone that would put a patch in the chamber after slathering the bore with hoppe's benchers...and forgot about it. Well, he got a ring where the patch was, that remained after cleaning. It was a stain.

Sometimes tool marks remain on the lands, especially on milsurp barrels. I've installed several NOS still in the wrap barrels...tool marks all the way down. can't be seen with the eye, very hard to see with a Birdseye camera, but if a set of marks line up in just the right way, looks like a ring.

On shotgun barrels, there is always a "ring" visible after cleaning. It's the end of the forcing cone though. the light is reflected differently and changes reflection abruptly at that spot. Not generally visible when dirty as reflection that area is uniformly poor.

I've seen shotgun barrels that bubba clamped too hard in his barrel vise. These can be swaged out with tapered index pins driven down the barrel. I very very much doubt such a thing could happen in a rifle barrel.

Broken bit, or other reason to change tools in the middle of production back when the barrel was made?

If it shoots good, don't worry about it. I've slugged even a brand new taken out of the wrap by me No.4 before shooting for the first time...and guess what. there was at least 2 places along the bore where resistance felt noticeably different.

Information

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[mrclark303]

I'll take a stab.
Warning: Cheaper bore cams can be misleading. I have a teslong, which can film birds-eye like yours as well as sideways. If you want to talk someone down in price...show them the Birdseye of the rifle they are selling. It always looks like crap. The reason is due to the reflective properties of the metal surface. After firing, no matter how much you clean, all of the metals microscopic 'imperfections' are going in the same direction. Makes even a new barrel look dull grey, perhaps even frosty (note I said microscopic. happens even on a brand new barrel after hand-lapping), whereas the side-view will show perfect, bright, and shiny.

I'm not saying you are wrong, just advising to double check. To double check without buying an expensive camera -- I would simply slug the bore. Before tapping my slug in, I would mark my driving rod for where to expect the flaw, and carefully note any difference in the force required to tap it through the area. Next, I would perform a straightness test. This involves dropping an index pin of a certain diameter and length down the bore. If it's in spec, it will fall all the way through with no resistance. Someone with a bigger library than me can pull up the spec for your rifle.

EDIT: here you go...https://pacifictoolandgauge.com/bore...lerances_-_001
and https://feeds.brownells.com/userdocs/learn/Inst-478.pdf

Some other general but related things about bore pictures I have noticed in the past:
It could be an illusion. I've heard first hand from someone that would put a patch in the chamber after slathering the bore with hoppe's benchers...and forgot about it. Well, he got a ring where the patch was, that remained after cleaning. It was a stain.

Sometimes tool marks remain on the lands, especially on milsurp barrels. I've installed several NOS still in the wrap barrels...tool marks all the way down. can't be seen with the eye, very hard to see with a Birdseye camera, but if a set of marks line up in just the right way, looks like a ring.

On shotgun barrels, there is always a "ring" visible after cleaning. It's the end of the forcing cone though. the light is reflected differently and changes reflection abruptly at that spot. Not generally visible when dirty as reflection that area is uniformly poor.

I've seen shotgun barrels that bubba clamped too hard in his barrel vise. These can be swaged out with tapered index pins driven down the barrel. I very very much doubt such a thing could happen in a rifle barrel.

Broken bit, or other reason to change tools in the middle of production back when the barrel was made?

If it shoots good, don't worry about it. I've slugged even a brand new taken out of the wrap by me No.4 before shooting for the first time...and guess what. there was at least 2 places along the bore where resistance felt noticeably different.

Many thanks for your thoughts, all taken on board, you can actually feel the bump on the 'ring' as the right angle of the camera probe glides over it, so it's not a mirage....

I'm minded to think this has always been there, it's as if the boring/ rifling bit was withdrawn and they just started again, a definitive circular step, although a very tiny one.

You can't see it by eye, no matter how hard you look.....