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What the Eye Can See

What the Eye Can See

A Look Inside Your Bore

The author using the Hawkeye to examine, in magnified detail, the inner walls of his rifle bore.

About 10 years ago, outdoor writer Jim Carmichel showed up at a prairie dog shoot in South Dakota with a truckload of rifles and a very interesting instrument that looked like something from the space program.

It was a long, thin, stainless steel tube attached to several cables with an eyepiece and a television monitor. It had a built-in lighting system and various optical attachments as well. Its purpose was to study--up close and in magnified detail--the interior of a rifle's barrel.

For the next two days we were torn between shooting prairie dogs and studying grooves, lands, corrosion and fouling through Jim's optical marvel.

The single aspect that really stands out in my mind was our steady destruction (all in the interests of science, of course) of the bore of a brand-new .220 Swift. The rifle was fresh off the rack when we arrived. For two days we shoved box after box of hot factory ammunition through it, and it was questionable which suffered the most, the prairie dogs or the rifle.

Each night we would put the long tube of the borescope into the barrel through the chamber and study how the steel was being gobbled away by hot loads in an already-sizzling bore.

It was, truly, a revelation--not only in terms of what a steady diet of red-hot ammunition will do to steel but also of the valuable information that can be gathered by a serious scientific instrument like a borescope.


The first mention I can find of such a piece of equipment is in the 1978 Gun Digest in which A.M. Wynne wrote about a borescope made by a company called Willrich. Because of the limitations of conventional photography at the time, he was unable to produce any actual images of the bore itself taken through the scope (although he did describe, in detail, what he saw through it in the study of two dozen different rifles).

The scope itself was a modification of the device doctors use to look in your eyes and ears. It had a long tube that projected light down into the bore and a system of mirrors that projected the image back to the optical eyepiece. The lighting system required a battery pack with cables.

Today the serious rifle nut who really wants to study his bore can do so much more easily, and with considerably more technical sophistication, using the Hawkeye Borescope from the Gradient Lens Corporation of Rochester, New York (home of Kodak and the optical capital of America).

The Hawkeye was the brainchild of Gradient's chief engineer. At the time, the company was involved in consulting on several defense projects, and the engineer (a devoted rifle shooter) concluded that some of the equipment they were using could be adapted for use on his favorite subjects. The resulting product was successful enough that today the Hawkeye Borescope is the sole product of Gradient Lens, an independent small company with about 15 employees.

The Hawkeye Borescope with right-angle viewing lens.

The Hawkeye is considerably simpler than either Wynne's borescope from the 1970s or Jim Carmichel's from 1996. The basic model consists of two stainless steel tubes of slightly different diameters, one of which slides over the other. Light is projected down one tube and reflected back to the eyepiece through the second. By rotating the outer tube, you can get a 360-degree view of a bore or follow one groove or land as it rotates as you pull the borescope out of the bore.

The eyepiece is similar to the familiar medical instrument, but Gradient goes one better and also offers a right-angle adapter to allow more comfortable viewing. Light is provided by a small flashlight that screws into the eyepiece and also serves as a handle. With no battery pack or cables and no television monitor, the whole outfit packs into a handy little carrying case that can easily be taken to gun shows, gunshops or anywhere else you might want to look at the bore of a rifle.

The Hawkeye does not end there, though, and right away it should be pointed out that it is not cheap. The standard instrument with right-angle eyepiece, which I have, sells as a package for $995. This model has a 17-inch tube, with an outside diameter of .188 inch--small enough for a .20-caliber bore but not a .177. The 17-inch length allows you to examine up to a 34-inch barrel, assuming you have access from both ends.

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 ( 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.

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