The trick I use is to run a cleaning rod in from the muzzle end, with the camera looking in from the chamber/throat. The reflection off the brass jag lights up the bore very nicely, and as you slide the cleaning rod aft, towards the camera, the reflection will highlight the lands and grooves remarkably well.

Mine is a Snap-On BK5500. Cost about a hundred bucks used and has a color monitor.

I tried one of those cheapie ones that plugs into your camera or computer. Resolution was pretty bad, but it only cost $30. You get what you pay for. On the bright side, it was small enough to fit down a 223 barrel. The Snap on won't fit down a 30 cal barrel.