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Firearms Examiner Training. Conrad W. 2013. Firearms Examiner Training.…
Firearms Examiner Training. Conrad W. 2013. Firearms Examiner Training. [Accessed 24 February 2020] from
https://firearms-examiner.training.nij.gov/module08/
.
Module 8: Examination of Firearms
I. Cycle-of-Fire Steps
A. Feeding
Can be manual or performed by various kinds of magazines and clips.
Insertion of cartridges into the chamber; the breech bolt pushes the cartridge into final position.
B. Chambering
Insertion of the cartridge into the chamber.
C. Locking
Most firearms are equipped with an interrupter mechanism that disconnects the trigger from the firing pin.
a. Making it impossible to fire until the mechanism is safely locked.
The breech bolt mechanism locks the cartridge into position in the barrel before firing.
D. Firing
When the breech is fully locked, a pull on the trigger mechanically translates to the firing pin release.
E. Obturation
When powder gases under high pressure are sealed to prevent them from jetting between primer cup and cartridge case, cartridge case and primer wall, and projectile and bore.
F. Unlocking
Reverse of the locking process and is frequently performed in conjunction with extraction.
G. Extraction
Extractor claws grasp the rim or groove of a cartridge case to extract the cartridge case from the chamber.
`1. Cartridge cases have a tendency to stick to the chamber after firing.
H. Ejection
Rotating on the fulcrum of the extractor, the case base is contacted on the opposite side by the ejector, which flips the case out of the actuating mechanism.
I. Cocking
The hammer spring is usually cocked when the bolt of a rifle, pistol, or repeater shotgun is retracted.
II. Evidence Receipt
A. Examination Documentation
Must be complete and accurate.
III. Firearms Identification Information
A. Includes
Brand name or trademark
Serial number
Model designation
Caliber designation
Importer, if applicable
B. Military Firearms
Typically don't have a caliber designation
Symbols and codes are used to identify the manufacturer.
C. Proof Marks
Some older foreign manufactured firearms will list a location, rather than a manufacturer.
D. Handguns
Revolvers
a. Most common types
ii. Double action
• Function
– Double-action revolvers allow the hammer to be cocked and released with a single pull of the trigger
– Most double-action revolvers have the capability to function in either the double- or single-action mode. However, some models are designed to fire in the double-action mode only; the hammer cannot be manually cocked and the trigger must be pulled.
– Used in the double-action mode, the cylinder is locked into place by the cylinder stop; the hammer does not lock into place since the cocking and releasing of the hammer is achieved in one motion.
• Ejection/extraction
– In double-action revolvers, the cylinder release device is generally located on the left rear of the frame, whereas in single-action revolvers, the loading gate is located on the right.
– By manipulating the release device, the cylinder will unlock and swing out to the left of the firearm. The front of the cylinder has an ejection rod, which is used to eject all the fired cartridge cases or cartridges from the cylinder with one movement.
i. Single action
• Modern ones generally include an integrated safety feature to prevent accidental discharge.
• Some single-action revolvers use a hammer block safety which, in the safe position, blocks contact between the cartridge and the hammer.
• Require manual cocking of the hammer before sufficient force on the trigger releases the firing mechanism.
b. Examination
i. Remove the cylinder (for double-action revolvers, open the cylinder)
ii. Inspect the cylinder for damage and smoke halos (may indicate which cylinder was fired last)
iii. Replace (in double action, close) the cylinder and check the functionality of the cylinder stop
• Cock the hammer until it locks and attempt to rotate the cylinder. (The cylinder stop located in the frame below the cylinder should hold the cylinder in alignment with the barrel.) Perform this check on all chambers.
• Manually hold the hammer to the rear while the cylinder stop is checked (double-action only (DAO) revolvers)
iv. Test the trigger pull
• Common methods
– Trigger weights
◊ Measuring trigger pull steps
4 more items...
– Spring scale
◊ Measuring trigger pull with a spring scale steps
4 more items...
– Digital scale
◊ Operate similarly to spring scales
v. Test the safety functions
• Should be documented
– Confirm that the revolver is empty
– Place a primed cartridge case into one of the cylinders
– Rotate the chamber so that it aligns with the barrel when the hammer is fully cocked
– Strike the trigger with enough force to release the hammer (but not so much force as to move the trigger all the way to the rear)
• If safety features functioning
– The hammer catches at the half-cock
– The transfer bar drops away from the firing pin
– The hammer block engages
• Ensure that the hammer and/or firing pin don't make contact with the primer
– If there are no marks on the primer to indicate contact with the firing pin, the safety functioned properly
– If there are marks on the primer, one or all of the safety features did not work properly
• If the primed case detonates, there are three possibilities
– The safety is not functioning properly; retest the firearm
◊ If the primed case detonates after retesting, improper function of the safety is confirmed
– The test was not performed properly; retest the firearm
– There is no safety feature present; examine the interior of the firearm to determine if a safety feature was present and subsequently removed
vi. Test fire the firearm
• General process
– Function
◊ Load firearm with one cartridge
◊ Announce intention to fire
◊ Discharge firearm
– Bullet recovery
◊ Properly mark cartridge case and bullets
◊ Determine appropriate recovery medium (water, cotton, etc.).
◊ Load firearm with one marked cartridge
◊ Place the firearm into the recovery system firing opening
◊ Announce intention to fire
◊ Discharge the firearm
◊ Repeat steps until number of test fires required (by laboratory policy) is complete
◊ Recover bullets and cartridge cases
– Additional Testing
◊ Full-automatic firing
◊ Single-action
◊ Double-action operation
– Revolvers
◊ In double-action revolvers with the capability of operating in single- or double-action mode, test fires should be obtained using both modes; markings may vary depending on the mode of discharge
– Firearms unsafe to discharge
◊ Using casting material, cast the barrel or the breech face firing area to provide microscopic detail for examination and comparison
• Drop Testing
– Process
◊ Place a one-inch-thick rubber pad onto a solid floor (such as concreter)
◊ Place a primed cartridge case in the chamber that will receive the hammer strike
◊ Cock the firearm
◊ Disengage the external safety
◊ Drop the firearm from a height of about three feet onto the pad
◊ Test all positions of the firearm - top, bottom, left side, right side, rear, and muzzle. (Before each drop, the primed case should be checked for firing pin indentations and the findings recorded)
– Outcomes
◊ The primed case does not detonate, indicating that the firearm will not discharge when dropped
◊ The prime case detonates
2 more items...
– Notes
◊ If the firearm is a double-action type, it should be tested in both single- and double-action modes
◊ If the firearm has an external safety device, it should be tested with the safety engaged
• Shock Test
– Modification of the drop test using a dead blow hammer
Pistols
a. Three types
i. Autoloading
• Semiautomatic
– Typically magazine-fed repeating firearms that require a separate pull of the trigger to fire each shot.
◊ The slide is pulled to the rear and released. This action
4 more items...
◊ Most semiautomatic pistols have one of three major actions
3 more items...
• Full automatic
– With a single trigger pull, pistols in full-automatic mode (with trigger fully depressed and cartridges in the feed system) do the following
◊ Fire the shot
◊ Extract and eject cartridge cases
◊ Continue the cycle (until ammunition is depleted or trigger is released)
◊ Feed cartridges
– Two categories
◊ Full automatic by design, with a selector switch that allows the shooter to fire in the full or semiautomatic mode
◊ Semiautomatic pistol modified to fire full automatic.
• Examination
– Determine the magazine capacity
◊ Load the magazine to capacity using dummy cartridges
◊ When no more dummy cartridges can be inserted into the magazine, the magazine should be placed into the firearm to ensure it will catch and function in the firearm
◊ If the magazine inserts and functions properly, the dummy cartridges should be removed, counted, and magazine capacity recorded.
– Cycle the action by pulling the slide to the rear and determine if a slide stop is present
◊ If present, lock slide to the rear; examine the extractor and ejector
◊ If not present, manually hold the slide to the rear; examine the extractor and ejector.
– Determine if the firearm is capable of full automatic fire
◊ Determine if a selector switch is present
2 more items...
◊ Cock the firing mechanism
◊ Pull the trigger and keep it pulled rearward
◊ Holding the trigger to the rear, pull the slide to the rear and release the slide
◊ Release the trigger
◊ Pull the trigger to the rear to release the firing mechanism; if the firing mechanism has already been released, then the firearm did not disconnect and it fired in full-automatic mode when the slide was manipulated when the trigger was pulled and kept it pulled rearward
– Test the trigger pull
◊ Common methods
3 more items...
– Test the safety functions
◊ Safety is functioning properly
5 more items...
◊ If the safety is functioning improperly (If the primed case detonates, the safety is not function properly)
5 more items...
◊ Test the disconnector
4 more items...
◊ The firing mechanism should not be released; the trigger should move forward and reset
4 more items...
– Test fire the firearm
◊ General process
4 more items...
◊ Drop Testing
3 more items...
◊ Shock Test
1 more item...
ii. Single- and multibarreled
• Designed to fire only one shot at a time.
• Examination
– Open the action and determine the capacity
– Test the trigger pull
◊ Common methods
3 more items...
– Test the safety functions
◊ If safety features functioning properly
5 more items...
◊ If safety features functioning improperly (If the primed case detonates, the safety is not function properly)
5 more items...
– Test fire the firearm
◊ General process
5 more items...
◊ Drop Testing
3 more items...
◊ Shock Test
1 more item...
Trigger Systems
a. Can have
i. Single-action trigger system
• Most common system
• Only function of the trigger is to discharge the firearm
• The firearm cannot be cocked by use of the trigger.
ii. Double-action trigger system
• The hammer can be at rest.
• Pulling the trigger cocks the hammer and fires the weapon.
iii. Double-action-only (DAO) trigger system
• Cocks and fires the firearm after each shot.
• The hammer returns to the rest position after each spot.
E. Long or Shoulder Firearms
Rifles
a. Action types
i. Bolt
ii. Pump (or slide)
iii. Autoloading
iv. Lever
v. Falling block
vi. Rolling block
b. Magazines
i. Removable box
ii. Internal box
iii. Rotary
iv. Tubular
c. Visual Examination: will determine
i. Type of magazine
ii. Type of action
iii. Caliber designation (this can be difficult to determine when examining foreign and/or military rifles because most are not marked with the caliber designation)
iv. Telescopic sights, (most of which have multiple adjustments within the scope)
• These settings should be recorded, including the variable magnification setting
v. Safety - most rifles have some type of external safety and possibly a disconnector safety.
Shotguns
a. Single-barrel
i. Action types
• Break open
• Pump (or slide)
• Bolt
• Semiautomatic (gas and recoil operated)
ii. Choke types
• Full (most restriction)
• Modified (some restriction)
• Cylinder (no restriction)
b. Double-barrel
i. Typically have a break open action
Examination
a. Determine the magazine capacity, if present
i. Load the magazine to capacity using dummy cartridges
ii. When no more dummy cartridges can be inserted into the magazine, the magazine should be placed into the firearm to ensure the magazine will catch and function in the firearm
iii. If the magazine can be inserted and functions properly, the dummy cartridges should be removed, counted, and the magazine capacity recorded.
b. Cycle the action to confirm proper functionality
c. Determine if the firearm is capable of full-automatic fire
d. Determine if a selector switch is present
i. If a selector switch is present, the firearm may be capable of full-automatic fire
• Perform full automatic functionality test according to laboratory protocols
– Determine automatic fire functionality
◊ Insert a minimum of three cartridges into the magazine
◊ Pull and hold the trigger to the rear; all three cartridges should fire
– Confirm automatic fire functionality
◊ Load a number of cartridges into the magazine
◊ Fire a short burst of full automatic fire and release the trigger
2 more items...
ii. If no selector switch present
• Perform full automatic functionality test according to laboratory protocols
– Determine automatic fire functionality
◊ Insert a minimum of three cartridges into the magazine
◊ Pull and hold the trigger to the rear; all three cartridges should fire
– Disassemble, examine, and document modifications
e. Cock the firearm
f. Pull the trigger
g. Holding the trigger to the rear, cycle the action
i. If the firing mechanism is released, the firearm may be capable of full-automatic fire
ii. If the firing mechanism is not released, the firearm is functioning properly
h. Determine the choke if the firearm is a shotgun
i. Check markings (if present) on barrel
ii. Measure interior diameter of muzzle
iii. If choke is adjustable, index the choke relative to the barrel using a metal scribe
i. Test the trigger pull
• Common methods
– Trigger weights
◊ Measuring trigger pull steps
∆ For single-action trigger pull, cock the firearm. For double-action trigger pull, do not cock the firearm
∆ Place the trigger under the top portion of the rod
∆ Slowly lift the firearm upward with the rod, bringing force on the trigger
2 more items...
∆ Continue until the least weight required to cause the firearm to discharge without the weights leaving the rest is determined.
– Spring scale
◊ Measuring trigger pull with a spring scale steps
∆ Cock the firearm
∆ Attach one end of the scale to a fixed object and position the other end against the trigger
∆ Slowly pull away from the fixed object until the firearm discharges
∆ Record the pounds of pressure required to discharge the firearm as indicated on the scale
– Digital scale
◊ Operate similarly to spring scales
j. Test the safety functions
i. If the safety features are functioning properly
• Check for an external safety device; this should be clearly marked in most long guns
• Confirm that the firearm is empty
• Function the action and cock the firearm
• Place the safety in the safe position
• Pull the trigger
ii. If the safety features are functioning improperly (If the primed case detonates, the safety is not function properly)
• Confirm that the long gun is empty
• Place a primed cartridge case in the chamber
• Function the action and cock the firearm
• Place the safety in the safe position
• Pull the trigger
iii. Test the connector (The firearm should not fire. If the long gun fails either the external safety or the disconnector test, it may still function, but not as designed.)
• Confirm that the long gun is empty
• Function the action and cock the firearm
• Ensure that the external safety is disengaged
• Pull the trigger and hold it to the rear while cocking the firearm. (The hammer or striker should not fall; the trigger should move forward and reset.)
• Cock the firearm again
• Disengage the external safety
• Open the action far enough to take it out of battery
• Pull the trigger
j. Test fire the firearm
i. General process
• Function
– Load firearm with one cartridge
– Announce intention to fire
– Discharge firearm
• Bullet recovery
– Properly mark cartridge case and bullets
– Determine appropriate recovery medium (water, cotton, etc.).
– Load firearm with one marked cartridge
– Place the firearm into the recovery system firing opening
– Announce intention to fire
– Discharge the firearm
– Repeat steps until number of test fires required (by laboratory policy) is complete
– Recover bullets and cartridge cases
• Additional Testing
– Full-automatic firing
– Single-action
– Double-action operation
• Rifles
– High-powered rifles can present difficulties in the recovery of fired bullets due to potential bullet fragmentation. Refer to laboratory policy for the correct methodology
• Firearms unsafe to discharge
– Using casting material, cast the barrel or the breech face firing area to provide microscopic detail for examination and comparison
ii. Drop Testing
• Process
– Place a one-inch-thick rubber pad onto a solid floor (such as concreter)
– Place a primed cartridge case in the chamber that will receive the hammer strike
– Cock the firearm
– Disengage the external safety
– Drop the firearm from a height of about three feet onto the pad
– Test all positions of the firearm - top, bottom, left side, right side, rear, and muzzle. (Before each drop, the primed case should be checked for firing pin indentations and the findings recorded)
• Outcomes
– The primed case does not detonate, indicating that the firearm will not discharge when dropped
– The prime case detonates
◊ Field strip the firearm
◊ Examine the major internal components to determine if there are any broken or missing parts
• Note
– If the firearm has an external safety device, it should be tested with the safety engaged
iii. Shock Test
• Modification of the drop test using a dead blow hammer
F. General Firearm Examination
Ensure that the firearm is unloaded
Determine the brand and model
Determine caliber designation
a. Measure the bore diameter
b. Measure the chamber, if possible
c. Research the type of design
d. Determine the country of origin (many of the older bolt-action rifles were manufactured for various countries, each of which used a different type of military ammunition)
e. Obtain the cartridge dimensions by casting the chamber, if necessary
Determine the action type
Determine the safety type
Determine if any modifications or alterations have been made
Observe anything else unusual about the firearm
Note the type of sighting system and any accessories present
Examine the bore (interior of the barrel) and determine class characteristics (number of lands and grooves and direction of twist)
a. Examine the interior of the bore to ensure it is free of projectiles
b. Check the bore for the possible presence of biological material or gunshot residue. If biological residues are present, notify the proper laboratory section
c. Check for bulges or damage to the bore
d. Examine the chamber and/or forcing cone area for damage or cracking
Test the trigger pull
a. Common methods
i. Trigger weights
• Measuring trigger pull steps
– For single-action trigger pull, cock the firearm. For double-action trigger pull, do not cock the firearm
– Place the trigger under the top portion of the rod
– Slowly lift the firearm upward with the rod, bringing force on the trigger
◊ If the weights come off the rest without the firearm discharging, add more weight to the rod
◊ If the firearm discharges before the weights come off the rest, remove weight from the rod
– Continue until the least weight required to cause the firearm to discharge without the weights leaving the rest is determined.
ii. Spring scale
• Measuring trigger pull with a spring scale steps
– Cock the firearm
– Attach one end of the scale to a fixed object and position the other end against the trigger
– Slowly pull away from the fixed object until the firearm discharges
– Record the pounds of pressure required to discharge the firearm as indicated on the scale
iii. Digital scale
• Operate similarly to spring scales
Test the safety feature
a. Fundamental safety rules when handling a firearm
i. Always keep a firearm pointed in a safe direction
ii. Always keep your finger off the trigger until ready to shoot
iii. Always keep a firearm unloaded until ready to use
b. In the laboratory
i. Be aware of all safety policies and procedures of the laboratory and their implementation
ii. Be responsible for your own safety and that of others in the working environment
iii. Handle every firearm as if it were loaded until it has been checked
iv. Follow the procedure for the particular laboratory regarding the receipt of loaded firearms
Test fire the firearm
a. General process
i. Function
• Load firearm with one cartridge
• Announce intention to fire
• Discharge firearm
ii. Bullet recovery
• Properly mark cartridge case and bullets
• Determine appropriate recovery medium (water, cotton, etc.).
• Load firearm with one marked cartridge
• Place the firearm into the recovery system firing opening
• Announce intention to fire
• Discharge the firearm
• Repeat steps until number of test fires required (by laboratory policy) is complete
• Recover bullets and cartridge cases
iii. Additional Testing
• Full-automatic firing
• Single-action
• Double-action operation
b. Drop Testing
i. Process
• Place a one-inch-thick rubber pad onto a solid floor (such as concreter)
• Place a primed cartridge case in the chamber that will receive the hammer strike
• Cock the firearm
• Disengage the external safety
• Drop the firearm from a height of about three feet onto the pad
• Test all positions of the firearm - top, bottom, left side, right side, rear, and muzzle. (Before each drop, the primed case should be checked for firing pin indentations and the findings recorded)
ii. Outcomes
• The primed case does not detonate, indicating that the firearm will not discharge when dropped
• The prime case detonates
– Field strip the firearm
– Examine the major internal components to determine if there are any broken or missing parts
iii. Notes
• If the firearm is a double-action type, it should be tested in both single- and double-action modes
• If the firearm has an external safety device, it should be tested with the safety engaged
c. Shock Test
i. Modification of the drop test using a dead blow hammer