AS i bought this USB micro-scope for something else, I have no idea what is on the mkt specifically for this purpose, but that some folks like to look at the bore. I don't think i'll be using it a lot.
Problem here is that the light and photo switch on the cord limits depth to about 20".
The bright light at the end of the tunnel is the reflection on my polished breech plug (not mirror, but taken to 1000-grit). The illumination source is the scope. The lights aren't full-on in that pic. Depth of field is short.
Supereyes is the logo on the side, around 30 bucks, .433" diameter-so 45 cal and up.
(tow and water then water displacing number 40, been loaded 5.5 weeks.)