Investigation

The borescope can tell you a lot about the quality of a new custom rifle barrel and it reveals which type of rifling you have, be it cut, button, or hammer forged. The borescope is not only for firearm barrels, we have used it to look inside cases for flash ­hole burrs and inside sizing dies to identify scratches. The borescope’s usefulness applies wherever there is a need to see into a small space where you normally could not see.

A gunsmith uses his borescope to check his chambering, crowning, or the quality of a custom barrel. It clearly reveals good reasons why barrels should be replaced. A gunsmith can check the interior of a bolt to see if a striker is rubbing where it should not be.

For competition shooters we use the borescope to check the smoothness of a new bore, the quality of the chambering, the effectiveness of his cleaning routine, the results of fire-lapping, the wear in a throat, or the amount of heat cracking down a barrel.

This is a view looking down the bore of a new, unfired button-rifled stainless .204 Ruger barrel.

This view is looking into the throat of a just-chambered barrel. It is the same barrel as photo number 1. Note how the rifling land diameter is not concentric with groove diameter.

These photos corroborate the evidence of non-concentric lands and grooves shown in photo number 2. In photo number 3, the bottom of the groove has been completely cut away. In photo number 4, taken at the opposite side of the barrel the bottom of the groove was not even touched by the chambering reamer during chambering, a barrel is spinning and the chambering reamer is stationary.

Even if the reamer is not true, or not in true alignment, the hole it makes would be the same all-around. In this instance it is not, revealing the barrel anomaly.

This is a close-up view of the same button-rifled barrel. The small evenly spaced lines are at right angles to the rifling. The small dark lines are reamer marks.

Between the small dark lines are the wider top edges of the reamer marks that have been ironed flat by the rifling button. With a Hawkeye you can even see the direction that the reamer marks have been ironed, laying them down like fish scales.

Direction of bullet travel should be in the same direction of rifling button pull (or push). Otherwise you would be pushing a bullet against the “fish scales” when firing the rifle.

This view is looking into the shoulder and case neck recess of a rifle chamber. Note how the recess is uniform.

This is a photo of a just-cut rifle chamber looking directly into the side of the barrel at the leade of a rifling land.

Note the lower edge of the land with steel smeared into the shape of a ragged tab by the chambering reamer.

This barrel is heat cracked with the often-mentioned appearance of alligator skin or scaling and has some moly fouling.

Note the chip in the edge of the land at a point lower left of center in the photo.

This is a view of heat cracking in the bore

This illustrates throat erosion just forward of the case mouth.

This is an example of throat erosion.

This barrel is pitted from rust.

This barrel is literally plated with bullet jacket fouling.

This portion of this barrel is heat cracked and severely fouled with black moly from the buffets’ coating.