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Gun Tube Tech
M1A2 MG school
| Question | Answer |
|---|---|
| What is the nomenclature of the gun tube? | M256A1 |
| What is the length of the gun tube? | 17ft 4in |
| What is the weight of the gun tube? | 2,502 lbs |
| What is the sling point of the gun tube? | 11ft 8in |
| How much does the bore evacuator weigh? | 28 lbs |
| What is the diameter of the bore? | 4.724in |
| How much does the breechring weigh? | 1506 lbs |
| What is the weight of the breach block? | 225 lbs |
| What are the 5 phases of function for the M256A1 gun? | 1. Manual opening 2. Automatic closing 3. Firing 4. Automatic opening 5. Extracting and ejecting |
| How do you rotate the breach operating handle? | -You rotate it from the 5 o'clock position upwards to the 12o'clock position -The breach mechanical shaft is rotated counter clockwise |
| What does moving the breech operating crank initially do? | Breaks the mechanical lock and allows the driver to drop down into the slot on top of the breach operating crank, releasing pressure on the firing pin allowing it to retract |
| What are the 4 main purposes of the recoil system? | 1. To absorb recoil energy 2. To provide a fixed length of recoil through all angles of EL 3. To return the gun to battery through all angles of EL 4. To hold the gun in battery through all angles of EL |
| What is the proper name of the recoil system? | Concentric hydrospring constant recoil system |
| Concentric means what? | The recoil system and the gun tube have a common center |
| Hydrospring means what? | The recoil system uses fluid displacement to absorb recoil energy and spring tension to return the gun to battery |
| What is constant recoil? | The recoil system provides a fixed or constant recoil of 12 inches through all angles of EL |
| What 3 purposes does the replenisher serve? | 1. Allows the crew to monitor the fluid level in the recoil system 2. Allows the crew to add or drain fluid as necessary 3. Replenishes the recoil system during firing |
| What are the 4 components of the recoil system? | 1. Replenisher 2. Gun cradle 3. Recoil spring 4. Piston |
| What is the length of the recoil spring before installed, installed but not compressed & installed but compressed? | -Before installed: 41in -Installed not compressed: 24.88in -Installed and compressed: 12.88in |
| How much FRH does the recoil system contain? | 10.4 gallons |
| What are the 3 functional components of the gun tube? | 1. Zone 1: the chamber region 2. Zone 2: the tapered zone 3. Zone 3: the bore |
| Describe zone 1 of the gun tube and its primary function | The chamber region begins at the breach face to a point 18 3/4 in into the cannon. Rear obturation occurs at the rear of the chamber region |
| Describe zone 2 of the gun tube and its primary function | -The tapered zone starts at 18 3/4in from the breech face & extends 22in into the gun tube -It's the transition between the chamber & the bore -Guides projectile into the bore -Provides fwd obturation by compressing the obturator seal on the projectile |
| Describe zone 3 of the gun tube | -The bore starts at 22in from the breech face and ends at the muzzle end of the gun tube |
| What 2 areas is the exterior of the cannon broken into and the purpose of each? | 1. Breach recess area: the threaded end of the cannon that is inserted into the breechring 2. External machined surfaces: surfaces of the cannon that are machined for fitting external components |
| How many holes are in the bore evacuator and what are their position? | -5 holes -Evenly spaced around the gun tube |
| At what angle are the holes in the bore evacuator drilled? | -30 degrees towards the muzzle |
| The bore evacuator is what kind of system? | -Eccentric pressure scavenging system |
| What is the purpose or function of the bore evacuator? | -It aids in the evacuation of spent propellant gasses |
| What is the operation of the chamber and bore? | 1. Initial detonation & cartridge case combustion 2. Rear obturation occurs 3. Fwd obturation occurs 4. Projectile fwd movement 5. Bore evacuator operation 6. Shot exit 7. Automatic breach ops 8. Extraction & ejection begin 9. Residual gasses evac |
| What PSI is the bore evacuator tested to? | 225 psi +/-5 psi |
| If the bore evacuator or breach is not operating properly, what will happen? | Flare backs may occur one the breach is opened due to gasses and propellant remaining in the gun tube |
| How many types of gun tube wear are there and what are they? | 1. Erosion 2. Eccentricity 3. Pitting 4. Cracking |
| What is erosion? | A complex phenomenon resulting from extreme chemical reactions under extreme temperatures and pressure that cause an enlarging or damaging of the bore due to firing. |
| What is the first indications of erosion? | Hairline cracks or checkering of the base metal |
| What is eccentricity? | the widening of "bell mouthing" of the bore near the muzzle |
| What is the condemnation criteria for eccentricity? | When the muzzle is widened enough to prevent proper boresighting |
| What are the two types of cracking? | 1. Interior 2. Exterior |
| Why do cracks grow worse? | From continued firing |
| What type of cracks condemn the gun tube? | Interior: cracks 1/8(.125) inch in length Exterior: cracks 1/4(.25) inch in length |
| What is pitting? | Damaging of the gun tube do to corrosion on the surfaces |
| What type of pitting condemns the gun tube interior? | -Zone 1: .03 inches deep or 20% of the total surface -Zone 2: .05 inches deep or 20% of the total surface -Zone 3: ignore pitting in zone 3 |
| What type of pitting condemns the gun tube exterior? | -Unpainted surfaces: .02 inches deep or 80% of the total surface -Painted surfaces: .04 inches deep or 80% of the total surface |
| What is the thickens of the chrome plating on the inside of the gun tube? | .5mm |
| Is chrome stripping, flaking or chipping permissible? | Yes |
| What is the purpose of the chrome lining in the gun tube? | To extend the life of the gun tube and delay erosion of the base metal |
| What is borescope? | An internal 360 degree visual inspection of the bore from the chamber to the muzzle |
| When should borescope be conducted? | -After every 150 EFC rounds after the first 300 EFC rounds have been fired -Within 180 days prior to firing -When troubleshooting indicates you should -Anytime a new cannon tube is installed, even if new -If you're not sure the tube has been inspected |
| What is the condemnation criteria fore the gun tube? | -1500 EFC rounds fired -5mm wear into the base metal |
| What is the condemnation criteria of the breechring? | 4500 EFC rounds fired |
| Why are recoil exercises conducted? | To re-establish the fluid film between the packing, seals and sliding surfaces |
| What is the length of the recoil spring before it is installed, installed and relaxed & installed and compressed? | -Before installed: 41 inches -Installed and relaxed: 24.88 inches -Installed and compressed: 12.88 inches |
| How often must a recoil exercise be conducted? | At least every 180 days |
| How is the recoil system exercised? | Back and forth 3 time 6-8 inches |
| What are the methods used to conduct a recoil exercise? | 1. Gun mount exercise kit 2. M3 oil pump 3. Firing one round (least preferred) |
| Recoil is defined as what? | The same force that propels the round towards the target drives the gun rearwards |
| What form is used to store historical gun data? | DA Form 2408-4 |
| How do you check to see if the breech actuator cable is adjusted correctly? | Use a feeler gauge between the operating lever and lug and the breech operating cam. The distance should be between .005 and .010 inches. |
| How far does the breech travel during recoil? | 12 inches |
| State the special life data found on the DA Form 2408-4. | Dual Condemnation Criteria, 1500 EFC rds or 5mm wear into the base metal. Borescope every 150 EFC rds. Breechring life 4500 EFC rds |
| When do DA Form 2408-4s have to be mailed into TACOM if AEPS is down? | -April 10th of each year -October 10th of each year |
Created by:
pmbussell