1) Walnut shells needed; apply within: This .308 case badly needs a good tumbling. 2) AR inferno: Dramatic heat checking and corrosion show evidence of harsh overuse, which could only be appreciated by Olin employees. 3) It looks like this .357 was fed cast lead first with a copper-jacketed chaser. 4) This is not a photo of the California treasury. Corrosion and rifling wear are evident in this AR-15 barrel and gas port.

The basic model with rigid steel tubes now comes in four different sizes, from the smallest diameter at .073 inch to the largest at .25 inch, in lengths ranging from two to 33 inches (not all diameters are available in all lengths, however). The tinier borescope will accommodate the smallest rifle bore but is available only in shorter lengths (two to eight inches).

There is a version with a flexible tube made of fiber optic cable, also in different diameters and up to 70 inches long.

A video attachment is available that connects the instrument to a television monitor for easier viewing, and this can also be turned into a digital video file; this system costs several thousand dollars.

A more recent development is a camera adapter that allows you either to create still digital images or video file up to 30 seconds long. There are adapters in different diameters that fit various cameras without retractable lenses, but a much more convenient option is to buy a package put together by Gradient that consists of a Sony Mavica digital camera, a bracket and all the bits and pieces necessary to make digital images. These can then be downloaded to a computer, printed, transmitted on the Internet, posted to a website--anything you might want. The whole digital-image package, including the Sony camera (but not the borescope), is $1,325.

Obviously, these instruments have a wide range of technical applications, not just rifle barrels, and many of the models and variations are intended for other uses such as automotive and machine parts. Anyone interested in acquiring one should visit Gradient's website (www.gradientlens.com) to see all the variations and technical specifications, which are far too numerous to list here.

For shooters, the obvious use of the borescope is to study rifle and shotgun bores, to see how much corrosion there is or the level of cuprous fouling, or to pinpoint the exact location of a rough spot that collects fouling. On a shotgun, you can study the chambers, forcing cones or chokes.

Without a borescope, the problem with looking down a bore to see how fouled it is, or how corroded, is the same as trying to look at a polished wooden table at a shallow angle. The light reflects off it in a glare, and you cannot even see the grain of the wood.

If you look at a rifle bore at the muzzle at right angles, you will see distinct copper fouling in a red smear, yet if you look down the bore, it will appear shiny and clean.

1) Ridden hard and put away wet: Age and use with corrosive primers show on the bore of this antebellum .30-caliber percussion musket. 2) "And just what are you growing in your rifle, Private?" Simple neglect in a .243 results in fouling and rust. 3) This old Mauser barrel shows the kind of pitting that can result from mixing corrosive primers and neglect. Note the worn land.

The borescope allows you to view the lands and grooves up to 17 inches down from the muzzle or up from the chamber and see what is really there.

Sometimes it is news you would rather not have. Looking at the bore of a cherished old rifle and finding that its rifling looks like the badlands of South Dakota is not terribly heart-warming. However, it is a great aid to efficient cleaning since you can spot the exact location of a rough spot that collects copper and concentrate your cleaning efforts right there rather than repeatedly scrubbing a bore that, for the most part, is already clean.

For serious target shooters (or gunmakers who build varmint and benchrest rifles), the borescope is a great help in breaking in a new barrel. With the barrel completely clean, you can fire one shot and then study, inch by inch, the entire length of each groove and land and spot any rough areas. These can be thoroughly cleaned before continuing with the shot-by-shot, constant cleaning regimen of breaking in a new barrel. The process becomes both quicker and more thorough.

The borescope has other uses as well. It can be used to examine the interior of a cartridge case to look for the beginnings of a case separation or to examine the interior of a loading die that is giving you trouble.

When you consider the number of tubular objects that play such an important role in rifle shooting, it is a wonder we were ever able to function without such a method of studying bores.