Possible ring in barrel?

[bud in pa]

If you go on line you can get an endoscope for your phone. just make sure that you get one with a long enough wire. I was able to use one on my phone, and my electrical usefulness is on par with Benjamin Franklin!

 

[chix2111]

If you get the Teslong bore scope there's no worries as the camera lens cable is 36" and the lens has an attachment for that makes it possible to home in on a specific spot on the bore tube.

 

[Boston123]

It tool me quite a few attempts, but I finally got a decent photo down the bore.

Amusingly, you can see multiple "rings" in this photo, maybe because the camera looks straight down the bore as opposed to when I look by eye (due to having to hold the flashlight up to the muzzle, i have to look down the barrel at an angle)

Like what painter and Eric Crewson say, it looks like the reflection of the edge of the breech plug, mirrored down the barrel.

 

[Grenadier1758]

View attachment 67835
Snap gauge set from Harbor freight less than $20. Useful for other stuff, too. Make sure the set includes one small enough to fit your bore. Slip the handle into a length of vinyl tubing to run the gauge down the bore.

a radius
The telescoping gauges are okay, but even the smallest one in the set has a diameter of the tip that is greater than the diameter of the barrel. It may only be a few thousandths off when compared to a measurement using a ball gauge set or pin gauge set or even the knife edges of a Vernier (digital, dial, or Vernier) caliper, it is still a measurement error.

These go up to 1/2" and the telescoping gauges will alow you to measure a larger diameter.

 

[Flinty Scot]

Chix2111, it'sa off the OP's issue, but what are the blocky marks, down the bore? Are they on the lands or the grooves? Is that tool chatter or something intentional? They look to me like either a ladder or a ratchetted track?
Thanks.

 

[toot]

my CURLY, gun has a shadow/ ring in it. not not worry.

 

[Whitworth]

Optical illusion due to reflected light rays interfering with each other. Something like "Newtons Rings".