I'm on my third digital borescope. The first one was the cheapest I could find on ebay. I was primarily interested in seeing how they worked plugging into my laptop. It was less than $10 and had a cable that was too flexible--no stiffness at all. Not one I would recommend, but I don't see anything on ebay like it now so that's probably best.
For the next one I got, I was specifically looking for one with a rigid cable and at least 4 feet long so I could see all the way to the breech plug in a long rifle. The brand I got was called Depstech. It was somewhere between $10-$15 at the time on ebay. The same thing looks like it goes for $35 and up now. I think it has an 8.5 mm diameter camera. It worked fine, but its focal length is 1.2 inch-3.2 inch, so one can only look straight ahead with it. It came with mirrors to look at 90 degree angles, but the focal length is too long to focus on the side of the bore. The rigid cable is over 16 feet long. Most of the ones I see on ebay now are wireless. Mine plugs into the USB port on my laptop.
This is an image from the Depstech.
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I wanted something that I could look 90 degrees at the rifling, meaning it had to have a real short focal length. I saw someone recommend a Teslong and it has the short focal length I was looking for. I got the NTG100 model. It cost $45.99 on Amazon when I got it but looks like it goes for $49.99 now. Ebay has them from $50 to $60.
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I like this Teslong NTG100. It has an even more rigid cable but still flexes. The probe is 45 inches long and is only 0.2 inches in diameter so it would fit into a .22 caliber bore. I would prefer a larger diameter camera for muzzleloaders, but it works. The focal length or depth of field is 0.4 inch, so I can see the rifling really well on the low side of the bore, but the side farthest from the camera is out of focus. You have to rotate the barrel to inspect 360 degrees around.
This is the one I like the best for the 90 degree view.
My experience has been that you get what you pay for. Less the $10 was barely passable. The $15 Depstech (now over $35) is good for looking at the breech plug face and seeing lengthwise down the rifling. I found it useful for looking for restrictions in a bore due to poor dovetail installation on one rifle. The $46 Teslong (now $50 to $60) is best for close inspection of grooves and lands and even goes down into the powder chamber in patent breeches. It satisfies my need for close inspection looking 90 degrees at the side of the bore. Just yesterday, I was using it to look at a large burr left from drilling for a vent liner in a flint patent breech. I could feel something prevent a small jag going all the way into the powder chamber but couldn't tell what it was until I looked through the borescope.
My images from the Teslong are on another computer or I would post some here. If it's important, I could transfer some images and post them later.
This has been my experience with digital borescopes. I've seen some really good photos posted by other people through their borescopes, so there may be better ones out there than what I have discussed here.
