Some time back I got a simple attachment from Wally World - it has a rubber cap from which goes a length of fiber optic. It goes on to a Mini Maglight and captures the light output - concentrates it at the end of the fiber optic - great for poking into the bore.
Other deal was a cheapie thing from a gun show - just a flashlight with a 90º bent acrylic rod stuck in the end - again - stuff that into chamber and look down.
One old trick which does work - put thumbnail down over chamber mouthat at slight angle, and under a good light source - sun or bright artificial light - it gives enough brightness to see quite a bit.