Capodastro,
Patches can sometimes polish the lead enough to make it appear shiny and smooth, so it is hard to see without a bore scope because of the low angle of light incidence you get looking down a bore. As mentioned, a pass with a bore brush will take that shine right off of it, so you can then see that it's different from the rest of the bore. Stuff right up near the throat or the muzzle can often be seen because of the color difference.
I've had excellent luck with the
No-Lead product. You put it in the bore and wait an hour and the lead turns to black crumbly stuff that patches right out.
Ethan.G
Those bullets might also bump up and do OK with a little more pressure. Using a faster powder to get to the same velocity, for example. Don't know what you were shooting. It's just another thing to try. Also try seating out to headspace on the bullet. That often reduces leading considerably if it doesn't interfere with feeding (see third image from left, below).
If that photo you posted is not yours and you didn't get permission to post it, you need to read the board
policy on posting copyrighted materials, too, and delete it if you don't have or can't get permission.
