I bought a Teslong NGT100 boroscope months ago and just got around to using it today. The head is about 5mm in diameter and easily fits into a 22 caliber or larger barrel. I have some mirror heads for it but I haven't used them yet. I often get frustrated with things like this and it happened today. The app demanded the model and it was not in any of the packaging. But eventually I got on line and figured it out. I looked at the barrels of my most accurate PCPs both of which have given me a 200 on the 30 yard challenge. I looked at my P35-22 and my Caiman X, also in 22 caliber. The first several pictures are the P35, the final few are the Caiman. The barrel on the Caiman is hammer forged, I think, and there seemed to be tiny copper flakes in the barrel. The P35 barrel seemed to have thread like lead deposits in some areas with some rectangular chunks near the crown. The Caiman had some much larger lead deposits about as deep as the rifling back near the throat. I gave both barrels at least 50 strokes with JB's bore paste on a patch. That cleaned up the P35 better than the Caiman. Too windy to see if I made a difference, I'm not expecting I did.