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LEARNING OBJECTIVES: Describe the required care and maintenance of naval gun barrels and the purpose of using the proper tools, gauges, and inspection instruments.

Every gun used in the Navy has a bore and chamber. Taking care of them is one of the first duties of the Gunner's Mate.

Care of the bore and chamber is no once-a-year or once-a-month matter. They must be cleaned, dried, and inspected before firing. They must be cleaned, inspected, and oiled weekly. They must be gauged periodically, and the bore must be decoppered when necessary. Maintenance of the bore and chamber is an important job-not ordinarily a very dificult one, but one that must be done properly and at the prescribed times.

Frequent reference has been made throughout the manual of the need for keeping your guns cleaned and lubricated. This has been done for a purpose-the need to emphasize the importance of your job in keeping your equipment "fire-ready."


With the exception of one or two small-arms weapons for which maintenance tools are usually issued separately, every naval gun is equipped with certain basic maintenance tools and accessories. Larger guns and mounts are, of course, equipped with more elaborate sets of tools, but all sets include, as a minimum, the implements that are required for care of the bore and chamber.

Cleaning Gear

The bore and chamber maintenance tools and

accessories issued for the 5"/54 are typical of such implements. The wire bore brush (with the sectional handle), the bristle sponge, and the lapping head are the basic cleaning instruments.

The sectional handle is a wooden rod with couplings at both ends that can be fitted either to similar couplings on other sections or to bore maintenance tools, like lapping heads and gauges. In the 5"/54 set, there are several of these sections supplied so that, by joining one to the other, you can make a pole of any appropriate length for the job at hand. The number of sections supplied with any gun makes any part of the bore accessible.

The bristle sponge is a cylindrical brush used for cleaning the bore and chamber. It fits onto the end of the sectional handle. When stowed, it is covered with a canvas protecting cap.

The lapping head is a cylindrical block on which can be mounted four removable spring-loaded segments. It is intended for removing relatively slight constrictions in the bore. In stubborn cases, you will need to use the wire bore brush. Its stiff steel wire bristles are effective in all but the very worst cases.

The tompion is used to keep dirt out of the gun bore and chamber. It is not used when there is a likelihood of condensation forming in the barrel with the muzzle plugged. It is also not used in wartime when there might not be time to remove it before firing. Sometimes plastic or canvas covers are used over the muzzle; the guns can fire through them if necessary (unless heavily ice-coated or if supersensitive nose fuses are used).


The bore plug gauge is a metal cylinder accurately machined so that it just passes through the bore when the gun is new. After the gun has been put to active use, constrictions may develop in the gun bore. The bore plug gauge is used to locate these constrictions. On guns of 5 inches or smaller, the bore plug gauge fits onto the end of a section handle in the same manner as the previously covered accessories or is attached to a line and pulled through the bore.

The bore erosion gauge is used in the gun barrel to measure the amount of erosion of the metal caused by firing.

NOTE: The Mk 9 Mod 0 projectile seating distance

(PSD) gauge was developed to repIace the 5" Mk 2 bore erosion gauge for estimating velocity losses and percent-expended conditions in all 5"/54 gun barrels.

The PSD gauge is similar in construction to the old Mk 2 bore erosion gauge. The major difference is that the PSD gauge measures the seating location of the projectile, rather than the wear near the origin of the bore. For instructions and use of the Mk 9 Mod 0 PSD gauge, see OP 1549, NAVSEAINST 8300. 1, and MRCs.

Inspection Instruments

Visual inspection of the bore and chamber precedes and folIows cleaning operations. Alight, of course, is very helpful in finding inadequately cleaned areas, pitted areas, rust or corrosion, deformed lands or rifling grooves, cracks, or other deviations. A bore searcher is used on 20 mm and larger guns. Look for corrosion at the muzzle end caused by salt spray.

If the chromium plating in the chamber of the bore appears pitted, the combat systems officer will decide if it is bad enough to need replating.


To prepare the gun for firing, you must inspect and clean the bore and chamber. Removal of the lubricant and the muzzle cover, or tompion, is but one of the operations in the preparation for firing.

Removing the muzzle cover, or tompion, is easy. To clean out the bore, however, you must wipe away the lubricant coating. In small arms, as you remember, this is done with a cleaning rod and a patch. In larger guns, you use the sectional handle instead of a cleaning rod and clean toweling wrapped around the bristle sponge in place of the patch. But the idea is exactly the same.

These instructions apply to guns that have been in use and were given afterfiring care when last used If you are preparing a gun barrel that has been taken from stowage or if it is a new one, you have much more work to do. The preservative used on new or stowed barrels must be removed with dry-cleaning solvent. When all the preservative has been removed, the solvent must be wiped out of the gun.


Observe ventilation and fire precaution rules when using dry-cleaning solvents. Remember also that solvents are drying and irritating to the skin and destructive to rubber and insulation.


Afterfiring care is more elaborate than prefiring care. Every time a gun is fired, something besides the cartridge case is left behind. Deposits of corrosive salts (powder fouling) are left on the interior of the bore and the chamber. As the rifling cuts into the projectile rotating band, some of the metal of the rotating band is left behind as a deposit of copper in the bore (metal fouling or copper fouling). Both kinds of deposits are harmful and must be removed.

Standard maintenance procedure (postfiring maintenance) is to remove the dirt and powder foulings by washing out the bore and chamber with a Break-Free solution (CLP#7) that cleans, lubricates, and preserves in one application. The gun is then secured until the next firing or a scheduled maintenance action. Pre- and postfiring barrel maintenance requirements are listed in detail on the appropriate MRC, normally a situation requirement (R) card.


Weekly maintenance is principally concerned with inspecting the bore and the, chamber for signs of corrosion and renewing the coating of oil. Decoppering and gauging may also be done at the time of weekly inspection although they are usually apart of the before and afterfiring routine. Weekly maintenance is particularly important during periods when the gun is not being fired every day.


The plug gauge, described earlier, is used with guns 3 inches and larger for detecting constriction of the bore. After the bore has been cleaned, attach the gauge to the extended sectional handle and pass it carefully through the muzzle until it clears the chamber end. If it passes through smoothly, the bore is not constricted.

If the bore has been constricted by copper fouling, the gauge will not pass. The next step is to mark the part of the sectional handle that is flush with the muzzle end to locate the constriction. Then draw out the gauge, remove it from the sectional handle, and attach the lapping head in its place. Push it into the gun bore up to the mark you placed on the handle and rotate it in the constricted area. Use the cylindrical segments for the lands and the rifled segments for the grooves. A mixture of pumice and oil maybe used as an abrasive. Continue lapping until the bore gauge will pass freely. Never try to force the gauge through the bore; it may stick, causing damage to both bore and gauge.

The plug gauge is the gauge you will use most in maintenance of gun bores. But there are other gauges-headspace gauges, breech bore gauges, and star gauges.

Information about the types and uses of gauges is in system Ops and ODS.


We have already described the use of lapping heads and a fine wire brush (0.003-inch wires) to remove copper deposits in gun barrels. If the constriction is not removed after a few trials with the lapping head, the decoppering head maybe used. These are mechanical or abrasive methods.

If there is metallic lead in the propellant, there is much less copper fouling when the round is fired. That is why older propelling charges were manufactured with lead foil in the case. However, the lead causes flash, and the more lead, the brighter the flash, which you do not want. To keep the flash to a minimum, you must keep the lead in most charges to a minimum. Propelling charges now being manufactured contain lead salts for decoppering effect.


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