Cheap borescope

Where else but at super cheap :)

10 mm dia, illuminated and can save your barrel throat erosion videos on your computer.

Featured Product: SCA 7M USB Inspection Camera - YouTube

This one has a 7 mm outside diameter.

http://m.youtube.com/watch?v=40dstqpjF0Y&feature=fvwrel

Been using one like that for quite a while. Got mine at Jcar for about $30. Lots of smaller ones (6mm) on ebay. Looking into one of those.
Qite interseting findings when poking one around the receiver area of some rifles.