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NIJ, Firearm's Examiner Course, Modules 3 and Module 4, retrieved Jan…
NIJ, Firearm's Examiner Course, Modules 3 and Module 4, retrieved Jan 28, 2020 ,https://firearms-examiner.training.nij.gov/
© Sara Hancock, Jan 2020
Propellants, Ammunition, and Firearms Development
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Firearms: Requires some means of predictably igniting a propellant, some device to facilitate the weapon being held and controlled, and a hollow tube for holding the propellant and projectile.
Components:
- Lock: ignition device
- Stock: added support
- Barrel: hollow tube
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Internal Ballistics Considerations: ignition, pressure, function of chamber design, chamber and cartridge dimensions, headspace consideration.
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Development:
- Ignition Systems
- Rifled gun barrels
- Breech-loading systems
- Repeating mechanisms
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Rifled Barrels: Rifling's are spiraled grooves on the inner surface of the barrel. It spin-stabilized the bullet.
Pennsylvania gunsmiths introduced use of tallow-soaked cloth or buckskin patches that made up the size difference between the ball and the barrel. The patch ensured that the powder remained behind the ball/bullet.
Shotguns:the place of powder charge meant it could be loaded with variety of size balls. Used in military units, hunters, and target shooters.
Breech-loading System:Transition from percussion cap to self-contained cartridge.
Needed:
- Hammer blow transferred to interior
- Arm had to be breech loaded
- Locking mechanism on arm required to contain cartridge
A weak point of percussion breech loading was the breech sealing. The shooter could be blasted in the face and eyes by hot gas. The tolerance of the breech mechanism needs to be loose enough to function under dirty conditions, and the sealing must be accomplished by expansion of the soft brass cartridge during firing.
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Actions
Top Break: barrel hinged to a separate frame that was operated by withdrawing a locking bolt to let the barrel tip down.
Falling Block: More powerful cartridge, frame slotted for breech block to slide down for loading and firing
Rolling Block: named for movement of breech block that rotates about 100 degrees to expose chamber for loading.
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Mauser: Had better safety mechanism than Mannlichers. Solid bridge provided support point for stripped clips to facilitate faster loading.
Repeating Mechanisms: A firearm that carried a supply of ammo and has means to move cartridges in and out of a single chamber.
Types of Firearms
Handgun: Cylindrical chamber with charge holes parallel to the long axis cylinder. Reliable percussion ignition allowed concentrating task of indexing cylinder behind the barrel.
Shoulder Arms: Firearms with long bolts that extracts a fired case from the chamber. Some are slide actioned which unlocked and opened for ejection and reload.
Box Magazine: magazines hold a large number of cartridges under the barrel. The cartridges are stacked vertically.
Automatic/Semiautomatic: Operates by an unlocked recoil-operated action called blowback. Based on the movement, it is either short recoil or long recoil.
Gas Operated: The gas from the barrel is redirected to work the repeating mechanism. The size of port depends on the position down the barrel, the operating pressure of the cartridge, and the rate of decreasing pressure.
Machine Guns: fire cartridges and have a locking system to secure breech. Usually a slower cyclic rate of fire, can be fed.
Ammunition:
- Propellant
- Projectile
- Cartridge cases
- Primer
Types
Fixed ammunition: propellant, projectile, and primer held together by cartridge.
Semifixed ammunition: artillery ammunition with separate components.
Projectiles: the component that does the work of the firearm.
The earliest projectiles were ball-shaped stones that eventually were replaced by common metal. Everything was scaled down to fit several types of firearms.
Cylindrical bullets eventually developed which Charles C. E Mini combined with the concept of an undersized ball. This increased accuracy, better gas sealing, and rapid loading.
Bullet Jackets: material surrounding bullet. Was first a cloth patch around the balls which caused bullet to spin. Eventually metallic bullet jackets developed that preserved integrity of bullet, facilitated engagement of rifling, and allowed rapid firing of bullets.
Two types:
- semi-jacketed: provide controlled expansion
- full metal: rigid tips feed reliably into chamber
Cartridge Case: contains other components, resists firing-pin blow during ignition, forms gas seal. The modern cartridge is flexible and expands under pressure to seal the rear of the barrel. It can remain intact at high pressures.
Naming Systems
North America has no defined naming system.
In Europe, the naming system is controlled by government agencies.
Case Design: The shape is linked to firearm evolution. Early cases were straight walled which gave way into bottlenecked cases, then rimless belted cases next.
Early Metallic
Flobert developed low-power cartridges known as rimfire. Rimfire was later improved on by Smith and Wesson.
Pinfire ignition was popular in Europe. However, to use it the gun must be slotted for pins.
Needle-fire systems placed the primer in the base of the bullet but the gas seal was insufficient.
Rimfire: Supplemental in US civil war because of simplicity in design and manufacturing. Early cartridges misfired frequently.
Centerfire: Pellet placed in the center of the cartridge base. Usually have a separate metal structure carrying pellet. Required thin and flexible casing.
Primer Pocket/Folded Head: Has central pocket for primer and anvil surface which activated priming compound when pin was struck. Case failed at fold over repeated use.
Balloon-Head: Modern case. Rim was forged, not folded to allow the primer pocket to balloon into the powders space. The only real failures were after repeated and extensive use. The solid head case eventually replaced balloon-head because the area around the primer pocket was filled in.
Modern Day: Boxer priming placed the anvil in the primer. Berdan priming makes the anvil part of the case.
Several materials are used including aluminum, brass, and mild steel.
Hybrid cartridge cases have a body of paper/plastic, plastic or composition base wad around primer, and thin metal base section to provide grip.
Primers: provided heat source to ignite propellant charge. Modern primers are chemicals. They provide an initial spark/flame, establish preignition pressure, and provide the gas seal. Mercury fulminate was commonly used but was replaced by potassium chlorate.
Smokeless Primers: Lead styphnate used because it did not produce corrosive residues. A combo of lead styphnate, antimony sulfide, and barium nitrate worked best. The combo can include sensitized, finely powdered aluminum, organic binder, and dye.
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Shotshell Primer: Case is largely nonmetallic so a battery cup is added to support the anvil and the flash hole has a paper or thin plastic cover.
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