Forensic Ballistics Exam Notes - revision session

Exam Reminders and Guidelines

• Checklists and Processes: Remember to review your checklists and processes before the examination.

• Prohibited Items: Be aware of items not allowed in the exam hall. Refer to the CHEM 5001 Moodle pages for a list.

• Smartwatches: Smartwatches are not permitted.

• Pencil Cases: Use only clear pencil cases, if needed.

• Calculators: Scientific calculators are allowed, but remove the lids.

• Punctuality: Arrive on time to allow time to settle and prepare mentally.

• Exam Materials: Do not touch the exam paper and booklets until instructed.

• Student Card: Bring your student card, which contains your examination number.

Answer Booklets

• Examination Number: Write your examination number, not your student number, on the front of each booklet.

• Separate Booklets: Use a separate booklet for each question.

• Question Allocation: Answer all of question one in one booklet, all of question two goes in a different booklet, and so on.

• Number of Questions: Answer four out of the five questions available in the ballistics exam.

• Additional Booklets: If you attempt the fifth question, request an additional booklet from the invigilators.

• Best Four: If you answer all five questions, the best four will be graded.

• Examination Instructions: Pay attention to the instructions on the front of each exam paper to see how to complete each section.

Answering Questions

• Mistakes: If you make a mistake, do not get annoyed; simply put a line through it and continue.

• Additional Space: If you run out of space, request another booklet and continue with the same question number.

• Methodical Writing: Write methodically, step by step, clearly showing your work.

• Clarity: Ensure clarity in your calculations and explanations.

• Marking: The examiner will look for all possible marks, but clarity is essential to facilitate grading.

General Exam Questions

• Spellings: Spelling errors will be forgiven if the meaning is clear.

• Technical Terms: Hybrid or confused technical terms may not receive full marks.

• Drawings: Drawings are encouraged and can be beneficial, especially when labeled and relevant to the question.

Knowledge from Stage One

• Building on Prior Knowledge: Stage two topics rely on knowledge from stage one.

• Not Explicitly Tested: There won't be a specific question directly related to the material from stage one, but knowing a combination of subjects will help.

• Re-Emphasis: Stage one concepts will be re-emphasized throughout the modules/course.

Calculation Questions: Trajectories

• Types of Calculation: Two main types: top-down view with crosswinds and side-on trajectory (SUVAT type).

• Exam Paper: Focus on questions 4 and 5 from the 2020 exam paper.

• Question 4 Scenario: Medieval reenactment event with a crossbow target shooting competition.

• Given Information: Distance to target, velocity of crossbow bolts, crosswind velocity, and angle.

Crosswind Calculation

• Scenario: Calculate the lateral deviation due to a crosswind on a crossbow bolt.

• Diagram: Draw a diagram of the scenario, including the target, shooter, bolt direction, and crosswind.

• Coordinate Axes: Establish y-axis (bolt direction) and x-axis (perpendicular to y).

• Crosswind Angle: Note the crosswind angle of 30 degrees from the direction of the bolt (projectile path).

• Wind Velocity: Wind is going from left to right at 25 {km/h}.

• Distance: The shot to the target distance is 30 {m}.

• Bird's Eye View: It is useful to imagine a bird's eye view when performing these types of crosswind calculations and resolving vectors.

• Unit Conversion: Convert all values to SI units (meters per second) to ensure compatibility. The SI unit of velocity is meters per second.

  • The velocity of the bolt is 300 {feet/second}.

  • To convert from feet per second to meters per second multiply by 0.3048.

  • 300 {ft/s} \times 0.3048 = 91.44 {m/s}

  • The velocity of the wind is 25 {km/h}.

  • To convert from kilometers per hour to meters per second multiply by 1000/3600

  • 25 {km/h} \times \frac{1000}{3600} = 6.94 {m/s}

• Total Velocity: Determine the total velocity, it's the total velocity amount between both the wind system and the bolt.

• Resolving Vectors: Resolve the vectors into x and y components to simplify calculations.

  • X direction is Vx = Vw \cos(60).

    • V_x = (6.94) \cos(60) \approx 3.472

  • Y direction is Vy = Vb + V_w \sin(60).

    • V_y = 91.44 + (6.94) \sin(60) \approx 97.454

• Angle Deviation: In this step the angle of deviation is calculated; that angle is based on combined values from both vectors.

  • \tan(\theta) = \frac{Vx}{Vy}

  • \theta = \tan^{-1}(\frac{Vx}{Vy})

    • \theta = \tan^{-1}(\frac{3.472}{97.454}) \approx 2.04 \t{degrees}

• Lateral Deviation: The last step is to combine with the distances to complete the vector calculation.

  • Draw a seperate distance diagram. In this you are given 30 meters to target.

  • \tan(\theta) = \frac{x}{30}

    • X = 30 \tan(2.04) \approx 1.07 \t{meters}

• Final Answer: The deviation amounts to about 1 meter to the right due to the crosswind.

Question 4B and 4C Wounding and Trauma on the Pelvic Region

• Pelvic Bone Trauma (Crossbow Bolt):

  • Describe the type of bone trauma that is expected. (e.g., chipping).

  • Provide the justification for the expectations.

• Pelvic Bone Trauma (High-Velocity Rifle Bullet):

  • Compare and contrast effects from both examples.

  • Discuss projectile and speed differences.

  • Understand that Kinetic energy equals \frac{1}{2} m v^2

  • Fully penetrating wounds will occur, as well as bevelling and cracking.

Classifying The Described Weapon

• The Law: The UK Law is sometimes a little uncertain and can be argued in a number of ways. It depends on what is being discussed (e.g., Previous casework).

• Begin with Section 2 (Shotguns): Always start by sectioning it as though it is in section 2 which has the most strict/explicit information.

• Measurements: Barrel length = 635 \t{mm} and Overall length = 1070 \t{mm}, Shotguns have specific lengths, this could potentially be one.

• Smooth Bore: The question describes the weapon is having a smooth bore which would put it within the shotguns classification.

• Bore Diameter: The bore diameter is 64 \t{mm}, under the firearm acts, shotguns must be under 2 inches ( 50mm} approximately).

• Final Classification: With a bore diameter above 2 inches there is no way for it to be put inside the section 2 act. With the nature and build of the system it is potentially a section one weapon. It must be argued that it follows the dimensions that allows classification as section one.

  • The barrel length must be larger than 30\t{cm}.

  • The overall length must be larger than 60\t{cm}.

Described Weapon Trajectory

• Scenario: Projectile fired into the sky at a 60 degree angle with a muzzle velocity of 200\t{m/s}.

• Vertical Distance: What will be the horizontal distance of the projectile given a building with a height of 20\t{meters}.

• Simplified Calculations (SUVAT): With air resistance is negated then basic SUVAT methods apply straight away.

• SUVAT Parameters:

  • S = Displacement, how far something has travelled.

  • U = Initial Velocity, this is how fast something is going to start with.

  • V = Final Velocity, simply how fast something is at the end.

  • A = Acceleration, the rate that velocity changes at.

  • T = Time, how long is this happening for.

• X Direction: Always use rate rather than SUVAT. This formula is simply rate = \frac{distance}{time}.

• Find Time: You can then user the time component to find out how long it will take to hit a specified object (e.g., height of a tower).

• Y Direction (Going Up):

  • S = ?, this is the variable we need to figure out how high max height is, so that we can take it off the tower at a later point.

  • U = 200* \sin (60) = 173.2 \t{m/s}.

  • V = 0, with this system we know that what goes up must come down, so when it stops at the top of it's trajectory we simply count backwards to find the landing point. It is important that is is stated that it is zero at max height when performing examination.

  • A = -9.8 \t{m/s^2}, we can't use a positive value, because the system is going up not down.

  • T = ? this variable is what we need to figure out to find the overall distance. In this section if is the time it takes to for the upwards trajectory.

  • SUVAT Formular is V = U + AT, simply rearranged to find T = \frac{V-U}{A}, T= \frac{0-173.2}{-9.8} = 17.67 \t{seconds}.

    • Once we have the final Time you can use the value to figure what the final displacement it. Formular for that task is V^2 = U^2 + 2AS, rearranged slightly to be S = \frac{V^2 - U^2}{2A}, with the values inserted gets the result S = 1530.612.

• Y Direction (Going Down):

  • S = 1530.612-20 = 1510.612 \t {meters}.

  • U = 0 \t{m/s}, initial velocity is zero as this is a falling motion only.

  • V = ?? What we are going to find.

  • A = 9.8\t{m/s^2}, as the projectile is going down so too is gravity.

  • T = ? What we need to find given these values.

  • SUVAT being used = S = UT + \frac{1}{2} A T^2, however in this circumstance the equation is simplified to S= \frac{1}{2} A T^2 to find the equation for T with the variable removed, now simply needs to be rearranged T = \sqrt{\frac{2S}{A}}, resulting in \sqrt{\frac{2*1510.612}{9.8}} = 17.55 seconds

    • New Step, given the upwards journey time and then the downwards journey time both need to be added together to find the overall time of flight.

    • Total Time T+=T then \frac{17.67 + 17.55}{1} = 35.232 \t{seconds}

• Total Horizontal Distance: Now we have our parameters, and we can find the solution for this projectile as it travel through the air.

  • Displacement X = \frac{velocityX * time}{1}

    • dX = \frac{200* Cos(60)*35.232}{1} = 3523\t{meter or approximately 3.5 kilometers}

Impact Velocity

• Final Stage Vector: To achieve, this step is mostly calculating and combining. Vectors to ensure the right values are achieved.

• Formulas

  • velocityY = U + AT

    • V = 0+(9.8*17,55) = 172m/s

  • velocityX = 200 * COS(60)

    • Combining vectors is an import part of this step, for it to achieved it must be performed using a particular method, known as Pythagoras. this method can be only used when working with right angle triangles ONLY. Vi = \sqrt{Vx^2 + V_y^2}

    • The formula can then be applied V_i = 199 \t{m/s}.

Tissue Simulants

• Types and Examples

  • Simulants: skin, soft tissue, hard tissue

Skin Simulants

• Examples

  • Leathers

  • Silicones

• Note: Silicones are more uniform.

Soft Tissue Simulants

• Examples

  • Ballistic gels

  • Synthetic gels

  • Soap

• Advantages

  • Synthetic gels can be re-used without issue.

  • Soaps give a visualisation of temporary cavities that open up.

Bone Simulants

• Examples

  • Polyurethane (cheap and expensive).

  • Multi-layered polyurethane (expensive syn bone).

Temporary Cavity

• Definitions

  • The result of the passing projectile.

  • A transfer of energy into radial acceleration.

  • Leads to tearing and braking points.

  • Transfers kinetic energy into a potential state.

  • Pulsation effects of elastic potential.

  • Can suck dirt and debris into the wound itself.

Exam Reminders and Guidelines

• Checklists and Processes: Remember to meticulously review your checklists and processes well in advance of the examination. Ensure all steps are understood and preparations are complete.

• Prohibited Items: Be acutely aware of items that are not permitted in the exam hall. A detailed list is available on the CHEM 5001 Moodle pages. Familiarize yourself with this list to avoid inadvertent violations.

• Smartwatches: Smartwatches are strictly not permitted due to their potential for misuse.

• Pencil Cases: Use only clear pencil cases to facilitate easy inspection by invigilators, if required.

• Calculators: Scientific calculators are allowed. Ensure that calculator lids are removed before the start of the exam.

• Punctuality: Arrive on time to allow adequate time to settle, organize your materials, and mentally prepare for the examination. Late arrivals may not be permitted to enter the exam hall.

• Exam Materials: Do not touch the exam paper and booklets until you are explicitly instructed to do so by the invigilator.

• Student Card: Bring your student card, which contains your examination number, and place it visibly on your desk for verification.

Answer Booklets

• Examination Number: Write your examination number, not your student number, clearly on the front of each booklet. Ensure the number is legible to avoid any confusion during grading.

• Separate Booklets: Use a separate booklet for each question to ensure clarity and organization of your answers.

• Question Allocation: Answer all parts of question one in one booklet, all parts of question two in a different booklet, and so on. Adhering to this instruction helps in streamlined grading.

• Number of Questions: Answer four out of the five questions available in the ballistics exam. Choose the four questions you are most confident in answering.

• Additional Booklets: If you attempt the fifth question, request an additional booklet from the invigilators. Clearly indicate on each booklet which question you are answering.

• Best Four: If you answer all five questions, the best four will be graded. Therefore, focus on providing thorough and accurate answers to the questions you select.

• Examination Instructions: Pay close attention to the instructions on the front of each exam paper to understand how to complete each section correctly. These instructions provide essential guidance for answering questions effectively.

Answering Questions

• Mistakes: If you make a mistake, do not become flustered; calmly put a neat line through it and continue with your answer. Avoid excessive scribbling, which can make your work difficult to read.

• Additional Space: If you run out of space in a booklet, request another booklet from the invigilators and continue with the same question number. Clearly indicate that the answer is continued on the additional booklet.

• Methodical Writing: Write methodically, step by step, clearly showing your work and the logic behind your solutions. This is particularly important for calculation-based questions.

• Clarity: Ensure clarity in your calculations and explanations. Define any symbols or notations used, and provide brief explanations to support your steps.

• Marking: The examiner will look for all possible marks. Clarity is essential to facilitate grading. Ensure your answers are well-structured and easy to follow.

General Exam Questions

• Spellings: Spelling errors will generally be forgiven if the meaning is clear. However, strive to use correct spelling to present a professional image.

• Technical Terms: Hybrid or confused technical terms may not receive full marks. Use precise and accurate technical language relevant to the subject.

• Drawings: Drawings are encouraged and can be highly beneficial, especially when they are clearly labeled and directly relevant to the question. Use diagrams to illustrate concepts or processes.

Knowledge from Stage One

• Building on Prior Knowledge: Stage two topics often build upon knowledge acquired during stage one. Review stage one material to reinforce your understanding.

• Not Explicitly Tested: There won't be specific questions directly related to the material from stage one. However, knowing a combination of subjects will enhance your ability to tackle complex problems.

• Re-Emphasis: Stage one concepts will be re-emphasized throughout the modules and course to reinforce their importance and relevance.

Calculation Questions: Trajectories

• Types of Calculation: Focus on two main types: top-down view with crosswinds and side-on trajectory (SUVAT type). Practice both types to build proficiency.

• Exam Paper: Pay particular attention to questions 4 and 5 from the 2020 exam paper as valuable examples.

• Question 4 Scenario: This question involves a medieval reenactment event with a crossbow target shooting competition. Understand the context and variables provided.

• Given Information: You will be given information such as the distance to the target, velocity of crossbow bolts, crosswind velocity, and angle. Note all given values accurately.

Crosswind Calculation

• Scenario: Calculate the lateral deviation due to a crosswind on a crossbow bolt. This requires understanding vector components and wind effects.

• Diagram: Draw a clear diagram of the scenario, including the target, shooter, bolt direction, and crosswind. Label all components for clarity.

• Coordinate Axes: Establish a y-axis (bolt direction) and an x-axis (perpendicular to y). These axes will help in resolving vector components.

• Crosswind Angle: Note the crosswind angle of 30 degrees from the direction of the bolt's projectile path. This angle is crucial for resolving wind velocity into components.

• Wind Velocity: The wind is blowing from left to right at 25 {km/h}. Convert this to meters per second for consistency.

• Distance: The distance of the shot to the target is 30 {m}. Ensure all distances are in meters for accurate calculations.

• Bird's Eye View: It is useful to imagine a bird's eye view when performing these types of crosswind calculations and resolving vectors, as this provides a clearer understanding of the geometry.

• Unit Conversion: Convert all values to SI units (meters per second) to ensure compatibility. The SI unit of velocity is meters per second.

  • The velocity of the bolt is 300 {feet/second}. Adhere to this conversion, you must use the units as part of your answer

  • To convert from feet per second to meters per second multiply by 0.3048.

  • 300 {ft/s} \times 0.3048 = 91.44 {m/s}

  • The velocity of the wind is 25 {km/h}. Adhere to this conversion, you must use the units as part of your answer

  • To convert from kilometers per hour to meters per second multiply by \frac{1000}{3600}

  • 25 {km/h} \times \frac{1000}{3600} = 6.94 {m/s}

• Total Velocity: Determine the total velocity by considering both the wind system and the bolt velocities combined. In this case, these are added by splitting them up into vectors.

• Resolving Vectors: Resolve the vectors into x and y components to simplify calculations.

  • X direction is Vx = Vw \cos(60).

  • V_x = (6.94) \cos(60) \approx 3.472

  • Y direction is Vy = Vb + V_w \sin(60).

  • V_y = 91.44 + (6.94) \sin(60) \approx 97.454

• Angle Deviation: In this step, the angle of deviation is calculated based on combined vector values.

  • \tan(\theta) = \frac{Vx}{Vy}

  • \theta = \tan^{-1}(\frac{Vx}{Vy})

  • \theta = \tan^{-1}(\frac{3.472}{97.454}) \approx 2.04 {degrees}

• Lateral Deviation: The final step is to combine with the distances to complete the vector calculation. Begin this stage by drawing a separate distance diagram for distance calculation.

  • \tan(\theta) = \frac{x}{30}

  • X = 30 \tan(2.04) \approx 1.07 {meters}

• Final Answer: The resulting deviation amounts to approximately 1 meter to the right due to the crosswind. Ensure your answer specifies the direction and magnitude of the deviation.

Question 4B and 4C Wounding and Trauma on the Pelvic Region

• Pelvic Bone Trauma (Crossbow Bolt):

  • Describe the type of bone trauma expected from this scenario (e.g., chipping). Include details like fracture patterns.

  • Provide a detailed justification for your expectations, referencing energy transfer and mechanisms of injury. Consider that a crossbow-fired projectile will cause less trauma than that of a bullet fired at high velocities.

• Pelvic Bone Trauma (High-Velocity Rifle Bullet):

  • Compare and contrast the effects of a crossbow bolt versus a high-velocity rifle bullet. High velocity rounds are determined to be those rounds that exceed 2000 ft/s.

  • Discuss the differences in projectile characteristics and speeds and their effects on bone trauma. Include specific details such as wound track size, fragmentation, entrance and exit wounds to produce a concise answer.

  • Understand that Kinetic energy equals \frac{1}{2} m v^2 and how this relates to the severity of wounds. More massive projectiles and greater velocities will cause more trauma to the intended target.

  • Fully penetrating wounds will occur, as well as bevelling and cracking. Explain the mechanisms behind these phenomena in the context of the question.

Classifying The Described Weapon

• The Law: Be aware that UK firearm legislation is complex and open to interpretation, often relying on specific case precedents. Always consider multiple angles.

• Begin with Section 2 (Shotguns): Always start by assessing whether the weapon could be classified under Section 2, which contains the most stringent criteria.

• Measurements: The provided dimensions are Barrel length = 635 {mm} and Overall length = 1070 {mm}. Shotguns have precise length requirements, which you should verify against the legal standards.

• Smooth Bore: The question states the weapon has a smooth bore, which is a typical characteristic of shotguns; smooth bore weapons have no rifling machinations inside the barrel.

• Bore Diameter: The bore diameter is 64 {mm}. Under the Firearms Act, shotguns must have a bore diameter less than 2 inches (approximately 50mm).

• Final Classification: Given the bore diameter exceeds 2 inches, the weapon cannot be classified under Section 2. Given the construction and attributes, classify the weapon under Section 1—provided it meets dimensional criteria.

  • The barrel length must be larger than 30 {cm}.

  • The overall length must be larger than 60 {cm}.

Described Weapon Trajectory

• Scenario: A projectile is fired into the sky at a 60 degree angle with a muzzle velocity of 200 {m/s}. Calculate the horizontal distance the projectile travels, given a building with a height of 20 {meters}.

• Simplified Calculations (SUVAT): Assuming air resistance is negligible, basic SUVAT equations can be applied. Note such assumptions for clarity.

• SUVAT Parameters:

  • S = Displacement, representing the distance traveled.

  • U = Initial Velocity, representing the starting velocity.

  • V = Final Velocity, representing the velocity at the end.

  • A = Acceleration, representing the rate of velocity change.

  • T = Time, the duration of action.

• X Direction: Always use rate instead of SUVAT formulas. The formula is rate = \frac{distance}{time}.

• Find Time: Use the computed time to determine the duration until impact with a specified height (e.g., a tower).

• Y Direction (Going Up):

  • S = ?, indicating we must find the maximum height to deduct the tower height later.

  • U = 200 \times \sin (60) = 173.2 {m/s}.

  • V = 0, as vertical velocity is zero at the trajectory's peak. Clearly stating this condition is important for an examination setting.

  • A = -9.8 {m/s^2}, utilizing a negative value because the projectile ascends against gravity.

  • T = ? requiring us to compute the ascent time.

  • SUVAT Formula: V = U + AT, rearranged to T = \frac{V-U}{A}, which calculates to T = \frac{0-173.2}{-9.8} = 17.67 {seconds}.

  • Once the final time is calculated, the displacement can be derived using V^2 = U^2 + 2AS, rearranged to S = \frac{V^2 - U^2}{2A}, which gives S = 1530.612.

• Y Direction (Going Down):

  • S = 1530.612-20 = 1510.612 {meters}.

  • U = 0 {m/s}, starting from rest as the projectile begins to descend.

  • V = ? to be calculated.

  • A = 9.8 {m/s^2}, as the projectile accelerates downwards due to gravity.

  • T = ? which needs to be found.

  • SUVAT formula used: S = UT + \frac{1}{2} A T^2, simplified to S= \frac{1}{2} A T^2 because U is zero. Solving for T gives: T = \sqrt{\frac{2S}{A}}, resulting in \sqrt{\frac{2 \times 1510.612}{9.8}} = 17.55 seconds

    • New Step, given the upwards journey time and then the downwards journey time both need to be added together to find the overall time of flight, this ensures the most accurate calculations

    • Total Time T+=T then \frac{17.67 + 17.55}{1} = 35.232 {seconds}

• Total Horizontal Distance: Using the calculated parameters, determine the projectile's horizontal range.

  • Displacement X = \frac{velocityX \times time}{1}

  • dX = \frac{200 \times Cos(60) \times 35.232}{1} = 3523 {meter or approximately 3.5 kilometers}

Impact Velocity

• Final Stage Vector: This step involves computing and synthesizing vectors to ascertain the correct impact velocity.

• Formulas

  • velocityY = U + AT

  • V = 0+(9.8 \times 17,55) = 172m/s

  • velocityX = 200 * COS(60)

  • Combining vectors requires Pythagoras' theorem, applicable exclusively to right-angled triangles: Vi = \sqrt{Vx^2 + V_y^2}

    • Applying the formula yields V_i = 199 {m/s}.

Tissue Simulants

• Types and Examples

  • Simulants: skin, soft tissue, hard tissue

Skin Simulants

• Examples

  • Leathers, cheap and easy to use depending on the application

  • Silicones, offer high degrees of replication for medical application. Offer great flexibility and can be easily molded

• Note: Silicones are more uniform than that leathers, which can provide a greater consistency for a lab based test that requires it.

Soft Tissue Simulants

• Examples

  • Ballistic gels, widely used in various forms of testing, but can be costly to produce.

  • Synthetic gels, often more cost effective, and offer similar results when compared to ballistic gels.

  • Soap

• Advantages

  • Synthetic gels can be re-used without issue and are simple to clean.

  • Soaps give a visualization of temporary cavities that open up.

Bone Simulants

• Examples

  • Polyurethane (cheap and expensive depending on application and requirements).

  • Multi-layered polyurethane (expensive syn bone, often used in live based medical procedures}.

Temporary Cavity

• Definitions

  • The result of the passing projectile, it describes the space that it passes through at any given time.

  • A transfer of energy into radial acceleration, what pushes everything outwards from the path. This depends on the type of round used (e.g., hollow point vs FMJ rounds).

  • Leads to tearing and braking points within organic material.

  • Transfers kinetic energy into a potential state, allows for the surrounding tissue