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ACOF (Abrams Master Gunner - 2016)
Terms in this set (130)
What is Ballistics?
The study of everything that happens to the projectile from the point of initial detonation of the round until the projectile comes to a complete stop.
What are the four phases of ballistics?
Internal ballistics, Transitional ballistics, External ballistics, Terminal ballistics
What does Internal ballistics deal with?
The projectile's behavior from the time the propellant's igniter is initiated until it exits the gun barrel.
What is obturation?
The means of preventing the escape of propellant gases over or through the breech closing arrangement (case base) or the projectile.
Static tube shape and muzzle displacement can influence what? What causes them?
The direction the round will take on shot exit. Static tube shape is caused by manufacturer irregularities. Muzzle displacement is caused by thermal bending and/or gravitational bending (droop).
What is In-bore Balloting?
Any transverse motion of a projectile in the gun tube.
What are the causes of in-bore balloting?
1. Projectile center of gravity (CG) and principal axis offset from the bore centerline. 2. Projectiles at manufacture are not perfectly concentric. 3. Projectile/gun tube clearances may exist at projectile surfaces. 4. Insufficient stiffness of the projectile/gun tube interface will exacerbate conditions caused by minimal balloting. 5. Projectile wear produces or widens gaps (clearances) between the projectile bourrelet surfaces and the gun bore. 6. Gun tube curvature (including bore irregularities) exist in all gun tubes. 7. Gas dynamics produce irregular pressures at the projectile base.
What is a bore evacuator?
A device on the gun barrel of a tank or AFV which helps prevent gases from venting back into the vehicle's fighting compartment when the gun breech opened to load another round.
How does a muzzle brake work?
By relieving the pressure that builds up in the barrel when a gun is fired. As the projectile accelerates down the barrel, it compresses the air in front of it toward the muzzle, increasing the pressure and turbulence in its path. The muzzle brake also directs gases propelled by the projectile outward to the sides, top and bottom, instead of releasing them in their natural path (straight ahead out of the muzzle in the path of the projectile). The net effect of the muzzle brake is to reduce recoil.
What are Transitional Ballistics?
Transition from internal to external ballistics and it describes the period from the instant the projectile leaves the muzzle, until the pressure behind the projectile is equalized and the propellant gases produced cease to have an effect on the projectile.
Describe Initial Yaw.
-Projectile initially leaves the muzzle, gases (no longer contained by obturator) rush past the projectile from its base to Ogive. -Projectile briefly experiences a tailwind which will cause it to try and tumble (so Ogive is facing gas flow). The gases only affect the projectile for a limited time so it will not tumble but will pitch and yaw. -Effects of the gases reduce, airflow reversed (ogive to base). The projectile will have moved offline due to reversed airflow striking projectile's side, slowing down the projectile and causing it to deviate from its intended line of flight. This deviation is termed initial yaw and is a major cause of the dispersion of rounds fired at the same point of aim.
What helps fin-stabilized rounds reduce initial yaw?
Closer tolerance in the manufacture of fin-stabilized rounds
What are External Ballistics?
The motion of the projectile under the effects of gravity and air resistance.
What are the three main methods free-flight projectiles can be stabilized?
Spin stabilization, Fin stabilization, Cone stabilization
Define Spin Stabilization.
Uses the gyroscope principle to stabilize the projectile by spinning it. Spin is achieved by rifling the barrel of the gun. This enables the projectile to be fired more accurately by controlling and minimizing the effects of gravity and air pressure (creates drift).
What is Drift?
The lateral deviation from the line of trajectory (AOB) due to the spinning of the projectile and the buildup of air pressure around the projectile nose. Drift direction is dependent upon the direction of the rifling. Drift is compensated for by CCF offset or offset in a ballistic reticle.
Describe Fin Stabilization.
Fin-stabilized rounds employ a set of fins at the rear of the sub-projectile that enables it to fly true to the target. To increase accuracy and minimize the effects of gravity and air pressure, the fin-stabilized projectile is spun at approximately 100 revolutions per minute (this slow spin is necessary because damage to the fins during separation of the sabots would cause the projectile to be steered offline). Fin Stabilized projectiles do not drift; the projectile tends to stay on the line trajectory so less compensation is needed with the sight reticle. Fin stabilized projectiles can be fired from smoothbore and rifled guns (rifled gun projectiles use slipping driving bands to minimize the effects of the rifling, as too much spin would reduce its stability).
What is Cone Stabilization?
A cone-stabilized round uses a cone shaped projection at the base of the projectile to induce drag, thus destabilizing the projectile at slower velocities which causes the round to tumble while in flight, reducing its overall range (limits the safety distance required for gunnery training). An example is M865 TPCSDS-T.
Why are sabot petals utilized?
To reduce in-bore balloting and smoothly carry the projectile in the gun tube.
Describe the interferences caused by sabot petal discard.
Damage to the projectile obturator or sabot petals may cause aerodynamic interference during the discard process and adversely affect the projectile trajectory. This will increase dispersion. Mechanical interference, such as sabot petals striking the fin assemblies, have the same effect. Proper inspection and careful handling of ammunition can prevent crew induced damage to the obturator and petals.
Define Terminal Ballistics.
Deals with the behavior of a projectile when it hits its target.
What is the most important consideration of terminal ballistics against armored targets?
What provides the greatest amount of penetration?
Focusing the largest amount of energy ono the smallest possible area of the target.
By what two means do armor-defeating projectiles achieve penetration of armored targets?
Kinetic Energy (KE) attack, Chemical Energy (CE) attack
How does a Kinetic round penetrate armor?
By concentrating maximum force on a single point.
What is Kinetic Energy?
The energy of motion
What is the formula to determine Kinetic Energy?
KE=Mass*(Velocity)2 / 2. As mass increases so does the KE. By doubling the velocity, the KE is increased by four times.
Why are modern tank guns smoothbore, not rifled?
Because practical rifling twists can only stabilize projectiles with a length to diameter ratio of 5:1 and also because the rifling adds friction and reduces velocity.
To get maximum force on the smallest area, antitank rounds have aspect ratios of what?
Length to diameter ratio of 10:1 or more.
KE penetrators are most effective when constructed how?
Constructed of a dense tough material, such as Tungsten or Depleted Uranium, and formed into a long, narrow, arrow-like projectile.
What is the length of the penetrator limited by?
The ability of the penetrator to withstand launch forces while in the bore and forces applied along its length at impact.
What are the three stages of Kinetic Energy penetration?
Setup, Penetration, Perforation
The initial contact the penetrator has with the target where a combination of mass and velocity are concentrated at a very small point (the tip of the penetrator). It is at this point the penetrator may posture itself to follow the path of least resistance.
At this point, the resulting force upon the target commences the penetration of the armor. The speed and effectiveness may be determined by the thickness of the target, its composition and density, other defensive aids, and countermeasures (ERA).
When the penetrator has violated the armor and achieved the desired effects associated with overpressure, intensive heat and the secondary effects of spalling. Crew could expect to be permanently incapacitated and the internal components of the vehicle rendered inoperative.
What is Chemical Energy (CE)?
Uses chemical reactions in order to cause penetration of a target. Most common forms of CE rounds are explosively formed projectiles (EFP) and HE projectiles (shaped charges).
What is a Shaped Charge?
A conical metal liner the projects a hypervelocity jet of metal able to penetrate into steel armor. In travel over long distances, the jet breaks up along its length into particles that drift out of alignment diminishing its effectiveness at a distance.
What is an Explosively Formed Projectile?
An explosive charge with a hollow lined cavity at one end and a detonator at the other. The detonating HE collapses the (often copper) liner into itself traveling at hypersonic speed (3000+ mps).
Explain the stages of Chemical Energy projectiles functioning.
On detonation of the CE warhead, energy is focused at the apex of the copper shaped cone, which collapses creating a high velocity shock wave of metal particles that penetrate the target through the process of erosion. CE projectiles can produce secondary effects of blast and shrapnel and provide anti-personnel and anti-material capability. Variations include the proximity (Doppler) fuse in air mode for MPAT and delaying function of obstacle reduction projectiles.
What are the three basic characteristics of vehicle design in relation to ballistic protection?
Firepower, protection, and mobility
Based on battlefield data, where is a vehicle most likely to be engaged?
The front, within an arc of approximately 1100 mils (62 degrees).
What are the purpose of Sloped Armor?
Allows a greater equivalent thickness to attack; less armor is used to provide the same protection; contributes to weight saving; at high angles of attack it may cause ricochet (solid shot AP ammunition this angle is about 1250 mils).
Describe Homogenous Armor.
Most vehicles have their basic structure formed from rolled homogenous armor for strength and toughness against general threats. Rolling the armor elongates the grain structure in the steel to form long lines, which enables the stress of the steel when loaded to flow throughout the metal and not be concentrated in one area.
What is Spaced Armor?
Armor protection in the form of plates is separated by gaps. Shockwaves generated by CE rounds are obstructed when they pass through the air gap onto the internal armor.
What is Compound/Composite Armor?
Consists of layers of different material such as DU, tungsten, RHA, plastics, ceramics, or air. It is lighter than all-metal equivalent armor and occupies a larger volume for the same resistance to penetration. The cost is prohibitively high restricting its use to especially vulnerable parts. Its primary purpose is to deter HEAT rounds.
What are the three types of Reactive Armor?
Explosive Reactive Armor (ERA), Non-energetic Reactive Armor and Non-Explosive Reactive Armor, Electric Reactive Armor
What is Explosive Reactive Armor?
Consists of a sheet or slab of HE sandwiched between two plates. On attack the explosive detonates forcibly driving the metal plates apart to damage the penetrator. Against a shaped charge, the projected plates disrupt the metallic jet penetrator, providing a greater path-length of material to be penetrated.
What is Non-energetic Reactive Armor/Non-Explosive Reactive Armor?
Operate similarly to ERA but without the explosive liner. Two metal plates sandwich an inert liner such as rubber. When struck by a shaped charge's metal jet, some of the impact energy is dissipated into the inert liner layer and the resulting high pressure causes a localized bending or bulging of the plates in the area of the impact. As the plates bulge, the point of jet impact shifts with the plate bulging. It uses energy from the shaped charge jet rather than from explosives.
What is Electric Reactive Armor?
Made up of two or more conductive plates separated by space/insulating material, creating a high-power capacitor. When penetrated, the capacitor is discharged, transferring a great deal of energy into the penetrator, which may vaporize it or even turn it into plasma, significantly diffusing the attack.
What is Bar Armor?
Armor designed to protect against antitank RPG attacks. Rigid grid of slates are placed around the vehicle at a predetermined distance (11-19 inches) and on impact will crush or capture the warhead or cause damage to the fusing mechanism to prevent detonation. The stand-off distance disrupts the formation of the high velocity jet of copper should a round strike. This type of armor is not effective against attacks by HE and fragmentation RPG that explode before hitting the cage as well as tandem-charge such as RPG-27 & 29.
Define Theory of Fire.
Links the relationship between the projectile in flight, the influences of the gun and the sighting system to achieve a target hit at any range.
What is the Principle of Elevation?
A projectile fired from a gun at an object in line with the axis of the bore (AOB) will not strike that object, but will fall short because of the influence of gravity and air resistance on the projectile during its flight. To compensate for this, it is necessary to point the gun above the object to be hit.
What are the Principal Definitions in the Principle of Elevation?
They deal with the main aspects of elevation. They are: Horizontal Plane, Axis of the Bore, Line of Sight, Angle of Sight, Tangent Elevation, Quadrant Elevation
Define Horizontal Plane.
The horizontal plane (HP) is an imaginary line drawn through the gun trunnions, parallel to the Earth's surface, but ignoring the curvature of that surface. It is the staft point of determining the amount of elevation required.
Define Axis of the Bore.
AOB is an imaginary line passing through the center of the bore.
Define Line of Sight.
The LOS is an imaginary line passing through the sight and the target.
Define Angle of Sight.
The AOS is the vertical angle formed between the LOS and the HP. When the LOS is above the HP, the angle formed is positive. When the LOS is below the HP, the angle formed is negative. The AOS governs whether more or less elevation is applied to the gun in order to hit the target. The tank cannot account for AOS.
Define Tangent Elevation.
The vertical angle formed between the LOS and the AOB when the gun is laid.
Define Quadrant Elevation.
The angle formed between the AOB and the HP when the gun is laid. It is a combination of TE, plus or minus the AOS.
What are the Secondary Definitions in the Principle of Elevation?
The aspects of principles of elevation that require consideration when the gun is fired. They are: Line of Departure, Jump Angle, Angle of Projection, Angle of Departure.
Define Line of Departure.
The line the projectile takes the instant it leaves the muzzle. Can be above or below the AOB depending on whether jump is positive or negative.
Define Jump Angle.
The vertical angle formed between the AOB and the LOD when the gun is fired. Caused by gun movement upon firing. The angle will vary depending on the gun and type of ammunition being fired.
Define Angle of Projection.
The vertical angle formed between the LOS and the LOD when the gun is fired. A combination of TE and jump.
Define Angle of Departure.
The angle formed between the HP and the LOD. A combination of QE and jump.
What are the factors affecting the angle of elevation?
1. Range to target 2. Elevation of the target 3. Jump 4. Gravitational Bending (droop) 5. Meteorological Influence 6. Muzzle velocity
How does Range to Target affect the angle of elevation?
The greater the range the further the projectile must travel and therefore, the longer gravity and air resistance can act upon it. To compensate for the increasing tendency of the round to drop short the TE is increased with increasing range.
How does Elevation of the Target affect the angle of elevation?
If the target is on the same level as the HP there is no AOS. If the target is above or below the HP, an AOS must be calculated and applied to the elevation factor in order to hit the target.
How can Jump be accounted for?
By using a CCF
What does the Jump Angle consist of?
Muzzle Point Angle (MP), Muzzle Crossing Velocity (CV), Center of Gravity Jump at the Muzzle, Aerodynamic Jump (AJ), Sabot Discard Jump (Sabot round only)
How does Gravitational Bending (droop) affect the angle of elevation?
Droop forms a vertical angle between the AOB at the breech and the AOB at the muzzle. Initial effects of droop can be overcome by zeroing. As the barrel heats up during firing droop will increase which can cause a low fall of shot and the gun may have to be re-boresighted or aimed slightly higher. If re-boresighting has occurred, it must be remembered that droop will decrease as the barrel cools down. The MRS enables the gunner to make field corrections for droop as necessary.
How does Meteorological Influence affect the angle of elevation?
The effects will vary depending on the gun and velocity of ammunition being fired. Wind may affect the air drag on a projectile and cause a decrease of velocity (range for a given angle of projection may vary). It is a small effect which only becomes significant at longer ranges. An increase in air density will decrease the velocity of the round (can be accounted for within the system, manual inputs).
How does Muzzle Velocity affect the angle of elevation?
The velocity of the projectile will determine the amount of elevation required to hit a target at a given range. A projectile with a low MV requires a larger AOP than one with a high MV because gravity and air resistance have a longer time to affect the projectile. Gun wear and charge temperature will affect MV. Hot propellant will burn faster and create more pressure than cold propellant. A change in MV results in the round traveling too far or falling short. Gun wear and charge temperature can be compensated for in a vehicle with a computerized FCS.
What factors affect line?
Drift, Throw-off, Crosswind, Trunnion Tilt (CANT)
How does Drift affect the angle of line?
Drift can cause a miss for line. It can be overcome through the use of ballistic sights and computerized FCS which compensate for drift within the reticle or computer. When firing using firing tables, a drift factor is normally included in the table.
How does Throw-Off affect the angle of line?
Throw-off refers to the horizontal angle formed between the AOB and the LOD when the gun is fired. It can be equated to jump in the HP. Throw-off can be compensated for during zeroing with sights.
How does Crosswind affect the angle of line?
A crosswind can force a projectile off its intended line of trajectory (moving laterally across the AOB). The greater the velocity of the wind and the longer the time of flight, the more effect the wind will have. Low and medium velocity rounds are more susceptible as are rounds that employ fin stabilization. As a result, the gun may have to be aimed off in AZ. FCS incorporate a crosswind sensor to assist in reducing the influence of crosswind but the wind at the gun is not the same as the wind at the target and the gunner may still have to apply an aim off.
How does Trunnion Tilt (CANT) affect the angle of line?
When one gun trunnion is higher than the other and quadrant elevation is applied to the gun, a line error will be introduced. This error is caused by the gun being elevated obliquely instead of on a vertical plane. Trunnion tilt not only causes a line error (deflection) but will also affect the amount of quadrant elevation applied in the vertical axis.
What is the Error Budget?
The influence of the hardware, environmental conditions, and human factors that affect accuracy and consistency.
Measures how close the mean point of impact of a number of rounds is to the point of aim.
The ability to strike close to the same point over a number of rounds in order to create a small shot group.
What are the three major categories of the error budget?
Fixed biases, Variable biases, Random errors
What is Fixed Bias?
Error sources induced by ammunition, weapon, and fire control system design and manufacturer that at any given range will cause the round to miss the desired aiming point in a constant direction. These errors are predictable and can be compensated for.
What are the Fixed Bias'?
System Parallax, Ballistic Drift, Mean Jump
What is Parallax?
The apparent movement, or difference in apparent direction, of an object as seen from two different points not on a straight line with that object.
What is System Parallax? What are the corrections for System Parallax?
The vertical and horizontal distance between the center line of the main gun and the optical axis of the sights. Corrections: GPS/CITV: computer calculates a correction from 200-4000 meters (M1A1), 200-5000 meters (M1A2) based on proper input of the correct tank to target range during boresighting. GAS: The system parallax is minimized on GAS by completing an accurate boresight at a set range of 1200m.
What is the amount of System Parallax between the GPS, CITV, TIS, and GAS and the axis of the bore?
GPS: Up 20", Right 29"; CITV: Up 26", Left 28"; TIS: Up 20", Right 35"; GAS Down 5", Right 12"
What is Ballistic Drift? What are the corrections?
Drift is the lateral deviation from the line of trajectory (AOB) due to the spinning of the projectile and the buildup of air pressure around the projectile nose. Projectiles will drift in the same direction as the spin caused by the rifling of the main (the largest contributing factor to ballistic drift is rifling). Corrections: GPS: the computer offsets drift in the ballistic solution. GAS: ballistic reticle.
What is Mean Jump? What are the corrections?
The average difference between the actual impact of a group of rounds fired over many occasions and the intended strike of those rounds, given that all inputs to the FCS are correct or within tolerance. The CCF consists of two numbers in x, y coordinate reflecting the horizontal and vertical offsets needed to null out mean jump in the respective axis. A CCF of 0,0 would equate to firing the system from boresight. Corrections: GPS/CITV: CCF, GAS: on a fully operational system it's corrected by conducting a Precision Alignment of the GAS. On a degraded system where the GPS cannot be used as a reference point the SCF should be used.
Define Variable Bias
Errors whose value remains nearly constant when firing one type of ammunition at a particular target at a given range (single engagement), but can change considerably from one engagement to the next.
What are the Variable Bias'?
Boresight/Boresight Retention, Cant, Crosswind, Fire Control, Air Density, Ballistic Solution, Muzzle velocity variations, Range Estimation, Optical Path Bending, Variable Jump, Zeroing Errors
What are Boresight/Boresight Retention errors?
What is the correction? Boresight initial errors can occur due to tolerances in the MBD, round-off in splitting means, or if the MBD operator and gunner are not sighting on exactly the same target aiming point. Boresight retention errors occur when the relationship between the end of the tube and GPS changes as in the case of gun tube droop, thermal bending of the gun tube, or turret deformation. Boresight retention can also be affected by inaccuracies in performing an MRS update. Correction in all sights is training.
What are the causes of Boresight Retention errors?
Gravitational bending (droop), Thermal bending, Turret deformation, Inaccurate MRS update, MBD tolerance, Round-off errors (mean readings), Gunner and/or TC not sighting on the same exact point (gun/sight)
What are Cant Errors? What are the corrections?
Occurs if the vehicle is on a side slope and one gun trunnion is higher than the other. When this happens quadrant elevation is applied to the gun a line error will be introduced. This line error is caused by the gun being elevated obliquely instead of on the vertical plane. Correction: GPS: POS/NAV, H/TPS, Cant unit as backup; GAS: manual correction (1/2 target form opposite direction of Cant for HEAT and MP-HE DM11 in azimuth only; no correction for KE/MPAT).
Describe Crosswind Errors. What are the corrections?
Wind moving laterally across the AOB can force a projectile off its intended line of trajectory. The greater the wind velocity and the longer time of flight, the more effect the wind will have. Correction: GPS: Crosswind sensor. GAS: no correction.
Describe Fire Control Errors. What are the corrections?
Errors and stresses of both physical and environmental nature applied to the various components of the fire control system. The FCS cannot compensate for most of these stresses such as design tolerances, metal fatigue, and vehicle vibrations. The FCS can compensate for muzzle displacement (thermal bending, gun tube droop). Thermal bending is normally caused by uneven cooling of a warm or hot barrel (one side cools more quickly than the other). Gun tube droop is from gravity acting on the gun and can disturb the gun-sight relationship established through boresighting. The thermal shroud minimizes thermal bending by up to 50% but does nothing about the gravitational effect. Corrections: good maintenance, frequent boresighting, MRS updates.
Describe Air Density Errors. What are the corrections?
Air density is the weight of a certain volume of air which consists of water vapor in the air, air temperature, and barometric pressure. Air density affects the ballistic characteristics of the projectile in flight during the external ballistics phase. It varies with temperature and altitude. The computer accepts data for barometric pressure and temperature and compensates for air density. Correction: manual inputs for barometric pressure and air temperature; no correction for water vapor. (no corrections in GAS)
Describe Ballistic Solution Errors. What are the corrections?
Errors associated with calculating a ballistic solution based on incorrect information applied to the computer by the crew or by the automatic inputs. Some of the incorrect inputs are: incorrect ammunition selected, incorrect range determined, unknown failure of an automatic input, incorrect CCF, H/TPS not alighted, incorrect ammo SUBDES, incorrect manual inputs. Correction: Ballistic solution as an error source is a training problem. Crews must be trained properly on: conduct of fire, maintenance.
Describe Muzzle Velocity Variations Errors. What are the corrections?
Changes in the velocity of the projectile due to characteristics of the ammunition or weapon. Muzzle velocity variations causes: tube wear (high number EFCs), propellant temperature, change of loading density, tube length, loss of muzzle velocity employing Canister in cold weather. Correction: good cannon maintenance, ammunition temperature input, good manufacturing procedures and quality control, good manufacturing and design.
Describe Range Estimation Errors. What are the corrections?
Errors associated with incorrect determination of a range to a specific target. When an incorrect range is introduced to the ballistic solution there will be an elevation error. Correction: training
Describe Optical Path Bending, its conditions, and corrections.
Optical path bending is the apparent illusion of target movement created by emitted solar radiation (commonly called refraction). Under certain light and environmental conditions the path of light (line-of-sight) may not appear to travel in a straight line. The point of aim taken up by the gunner, while it may appear to be correct, could be incorrect and result in rounds missing targets. Conditions: Day - clear skies, flat terrain, wind less than 10 MPH, ranges over 1500m. Night - clear skies, flat terrain, wind less than 4 MPH, ranges over 1500m. Corrections: Find an elevated firing position (at least 10m above intervening terrain), Day - aim ½ target form high, Night - aim ½ target form low.
Describe Variable Jump. What are the corrections?
The average difference between actual impacts for a particular occasion and the intended strike of those rounds, given all inputs to the FCS are correct or within tolerance. Correction: standard sight adjustments after subsequent round misses.
Describe Zeroing Errors. What are the corrections?
Zeroing is the firing technique used by the crew to align direct fire sights to the center of a shot group, known as the MPI. Any errors in zeroing will cause accuracy problems later on. Correction: training.
What is Random Error?
Random error sources are those that vary for each round fired. They cannot be predicted from one round to the next, nor can the crew compensate for them.
What are the Random Errors?
Round-to-round Dispersion, Gunnery Lay Error.
What is Round-to-Round Dispersion? What are the corrections?
Round-to-round dispersion refers to the spread between impacts of 2 or more rounds in relation to the MPI when fired under identical conditions. There is a spread of shots around a central point, this area is called the dispersion zone. As the range to the target increases so does the size of the dispersion zone. There is no way the crew can compensate for dispersion. Factors that may cause dispersion: crosswind, thermal bending, lot number. Correction: Re-engage (all sights). There is no compensation for dispersion, but using the reengage technique a target hit may result.
What is Gunner Lay Error? What are the corrections?
When the gunner fails to make a correct lay to the target aiming point while either boresighting or engaging targets. It is a significant error source and primarily a training problem. To reduce this error, each gunner must be trained to end his lay in elevation. Gunnery lay errors are influenced by: inability to identify the center of target, inability to properly superimpose the reticle on the center of target, firing too quickly due to criticality of time, optical path bending, parallax. Correction: training.
What are the prerequisites for LFAST?
1. PMCS 2. AACs 3. Boresighting with MBD 4. Collimation checks of the MBD 5. Plumb and sync (M1A2 only)
What is a boresight device?
An optical instrument used to accurately define the axis of the bore of a gun at the muzzle end.
What is the purpose of MBD collimation?
Makes boresighting faster and more accurate (50% more accurate).
What are the specifications of the MBD?
Magnification: 10x, Field of View: 4.5o (79.96 mils), Focal Range: 300", Adjustment: +1 to -4, Reticle Line Width: .06 mils with 1 mil circle, Weight w/o case: 9.75 lbs
When are MBD Collimation checks conducted?
Prior to boresighting, during routine maintenance
What are the conditions for MBD Collimation?
1. Hydraulic pressure 1500-1700 Psi 2. Turret power on 3. 500-1200 meter panel with defined right angle 4. Parallax shield if range less than 500 meters 5. Tolerance is 1 reticle line width
What are the reasons for loss of MBD Collimation?
Loose collimation screws, stripped collimation screws, inoperative MBD, mishandling of MBD, tube wear (bell mouthing)
What is the purpose of boresighting?
Boresighting establishes a base of information to make a system parallax correction by establishing a relationship between the axis of the bore and the sights. When the proper tank-to-target range is entered into the computer during boresighting, this gives the computer the baseline from which all later system parallax corrections will be made.
What are the two methods of boresighting?
MBD, Two point reference method (string method)
What are the GPS boresight adjustments?
The GPS allows up to 7.5 mils of movement in any direction, normally only less than 3 mils should be necessary to boresight. If more than 5 mils of movement are required recheck the procedure.
What is the frequency and conditions to boresighting?
Change of TC/Gunner, loss of boresight or demonstrated loss of accuracy, in training, before each gunnery table, in combat: before anticipated combat, after extensive road march, as the tactical situation permits
What is the purpose of CCFs?
Refine and improve the ballistic solutions and are obtained from stationary tank firings. They also correct for mean jump.
What are two ways to enter information into the GCDP?
Keypad, 4-way adjust buttons
What is boresight loss?
Any movement of the sights or gun away from the initial alignment.
What is boresighting loss caused by?
Shape changes due to heating and cooling; boresighting when the gun tube is warm, firing when the gun tube is cool; Firing or other shocks to the system; Changes in weather conditions
What is the most reliable method of correcting boresight loss?
Boresighting. The MRS is an alternate method available to use when time is of the essence.
Who makes up the proofing team?
The most technically proficient TCs, gunners and preferable an experienced turret mechanic
What are the duties of the proofing team?
At home station, assist training crews in procedures for live-fire gunnery; During screening test, assist in the preparation and conduct of the test.
What does the success of the proofing team depend on?
Eliminating the following before the first round is fired: mechanical faults, crew errors
How does a tank pass the screening test?
Hit one out of the first two rounds fired within the circle
What is an erratic round? What happens if the second strike is erratic?
The dispersion between strikes is more than the width or height of the circle. Stop the test and check the system.
What are the methods of zeroing?
Common zero, 500 meter zero
What is Common Zero? What are its advantages and disadvantages?
The zero value from different tanks are averaged together to create a zero value for the fleet. Advantages: overall accuracy is achieved, minimal expenditure of ammo. Disadvantages: less accurate with a specific tank; some crews will have less confidence in their system.
What is the 500 meter zero? What are its advantages and disadvantages?
An individual zero done at 500 meters. Advantages: less tank-to-target distance (easier for crew to identify holes in panel); when performed correctly, more accurate for a specific tank. Disadvantages: time consuming; requires large quantity of ammunition.
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