Gunnery Officer Gunnery Officer INFORMATION SHEET
MISFIRE PROCEDURES
Information Sheet Number: 1.17
INTRODUCTION
Personnel involved with the firing of the 5"/54 gun must be thoroughly familiar with NAVSEA SW300-BAC-SF-010. This is not a publication to reference after the fact. The controlling actions to be performed when a gun misfires are time critical and must be done right the first time to avoid personnel injury. This lesson discusses such controlling actions in various situations and the use of the predictor chart.
REFERENCES
(a) SW300-BAC-SF-010 Clearing Of Live Ammunition From Guns
INFORMATION
A. SAFETY MANUAL FOR CLEARING OF LIVE AMMUNITION FROM GUNS
1. This manual is divided into three (3) sections:
a. Chapter one: general information
b. Chapter two: misfire procedures for 7.62 mm thru 40 mm guns
c. Chapter three: misfire procedures for 76 mm and larger guns
2. The publication is useless if it is read for the first time after a misfire occurs.
3. A Gunnery Officer should be thoroughly familiar with misfire procedures and have the immediate controlling actions memorized.
B. GENERAL INFORMATION.
1. Purpose of publication.
a. Always refer to specific system technical manuals to be used in conjunction with this manual.
b. Gun systems installed aboard aircraft are not covered in this publication.
c. Notice to Gunnery Officers
(1) All misfire/hang-fire incidents will be handled as emergencies.
(2) When a misfire occurs maintain immediate/continuous communication between the mount and the point where decisions are to be made.
(3) During all firings, maintain two (2) charged fire hoses laid out on the deck.
(4) A concept of ten (10) minute safe clearing time exists.
C. DEFINITIONS
1. A "Cold gun" condition is when the gun barrel and chamber wall temperature have not been raised by prolonged firing to a point where cook-off can occur.
2. Cook-off occurs when components of the gun reach a temperature high enough to cause some form of explosive reaction in the projectile.
a. As long as the breech is closed, cook-off will cause the round to be fired in a near normal manner.
b. With the breechblock open, cook-off will result in personnel injuries/fatalities and major equipment damage.
3. Hang-fire occurs when there is a delay beyond the normal ignition time after the initiating action is taken (eg. the gun fires 15 seconds after the firing key is closed).
4. A "Hot gun" condition is when the gun barrel and chamber wall temperature have been raised through prolonged firing to the cook off point.
5. Safe firing bearing is the gun target line bearing maintained to preclude danger to other craft and friendly forces in the event of a cook-off.
D. EFFECTS ON AMMUNITION AND ASSESSMENT OF HAZARDS
1. In a hot gun, propellent cook-off can be expected prior to projectile explosive reaction.
a. Propellant casing walls are much thinner than projectile's walls.
b. Propellant charges ignite at lower temperatures than projectiles.
c. If the breechblock is closed, the hazard presented is relatively small.
2. The propellent charge must be removed prior to commencing internal barrel cooling.
a. Coolant water can obstruct the projectile in the event of a cook-off.
b. Breech failure can occur due to the resulting high pressures caused by impeded explosive gases.
c. The explosive pressure and gases could vent to the gun room.
E. EXPERIMENTAL COOK-OFF
1. The 5"/54 MK 45 LWGM under continuous sustained firing conditions will achieve cook off temperature in approximately 3 minutes.
2. When a misfire occurs, a determination must be made as to whether sufficient safe time is available in which to clear the gun.
3. To aide in the determination, use a 10 minute safe clearing time predictor.
4. The predictor is not a precise cook-off time indicator, it is only intended to indicate the relative degree of the possibility of cook off.
5. If the predictor indicates a safe clearing time of 10 minutes, operators should have 10 minutes from the time the round was inserted to remove it.
a. If the propellant charge can be extracted, commence INTERNAL cooling.
b. If the propellant charge cannot be extracted, commence EXTERNAL cooling only.
c. If there is a misfire, commence EXTERNAL cooling only.
6. If the predictor indicates less than 10 minutes, evacuate all personnel from the mount and adjacent spaces.
F. PREDICTOR PROCEDURES
1. Refer to figure 1.17-1
2. Divide total rounds fired by the duration time of firing in minutes. This is the X coordinate value.
3. The Y coordinate value is hundreds of rounds fired.
4. If the intersection of these 2 points is in the green area, this indicates that a 10 minute clearing time is available.
G. MISFIRE PROCEDURES
1. In the event of a misfire the following procedures should initiated:
a. The ten minute safe time is calculated from the time the round was chambered.
b. Wait 30 seconds after the last attempt to fire before opening the breech block to ensure against a hangfire.
2. The following steps must be completed in 40 seconds:
a. Report the time of misfire to Combat Information Center.
b. Ensure the gun is pointed to a safe line of fire.
c. Ensure the breech is fully closed.
d. Attempt to fire the gun using alternate circuits.
e. If the gun fails to fire, determine if gun is in a hot or cold condition.
H. HOT GUN PROCEDURES
1. Use the predictor to indicate safe clearing time.
a. If safe clearing time is less than 10 minutes, stop all attempts to clear the gun and evacuate.
b. Stay clear of the mount for 2 hours.
c. If safe clearing time is greater than 10 minutes:
(1) Commence external cooling only.
(2) Clear unnecessary personnel from the mount.
(3) Wait 30 seconds after the last attempt to fire, open breech block, and attempt to extract propellant charge in local control STEP Mode. Step Mode allows the operator step by step gun control manipulation.
(4) If it cannot be removed in 10 minutes, clear the mount.
(5) If the charge can be removed, throw it overboard.
(a) Load the clearing charge.
(b) Fire the gun on a safe firing bearing.
(c) If the round does not fire, clear the mount for 2 hours.
I. COLD GUN PROCEDURES
1. Wait 30 seconds after the last attempt to fire, then open the breech block and look for hangfire.
2. Extract propellant charge in STEP Mode.
3. Ensure the chamber is clear.
a. If the chamber is clear, fire on a safe firing bearing with a full service charge.
b. If the chamber is obstructed, use a reduced charge.
4. Ensure all obstructions are clear of recoiling parts.
5. Fire the gun.
J. IN THE EVENT OF A BORE EXPLOSION
1. The gun is not to be fired!
2. Use cold and hot gun precautionary measures.
3. Commence internal cooling.
4. If another round is chambered, attempt to remove propellant charge and let an Explosive Ordnance Team (EOD) team extract the loaded projectile. Use external cooling only.
K. SAFETY SUMMARY
1. Safety is everyone's responsibility.
2. The number 1 rule is, "if there is any doubt whether a hot or cold gun situation exists, follow hot gun procedures."
3. Both inert and explosive load projectiles are to be cleared through the bore.
4. In a hot gun, the 10 minute safe clearing time period is initiated when the round is chambered not when the mis-fire occurs (or when it is declared).
5. Do not attempt internal barrel cooling when the propelling charge is still in the chamber.
6. Always wait a minimum of thirty (30) seconds after the last unsuccessful attempt to fire prior to opening the breech block of the gun.