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Module 4: Modern Firearms Manufacture (MACHINING (drilling techniques for…
Module 4: Modern Firearms Manufacture
CASTING
molten metal is poured through a sprue hole of a sand mold to fill the cavities of the negative shape where it is allowed to cool; the part is removed for fine forming
fine forming prepares the firearm component for surface finishing and assembly
traditional alloys used for firearms manufacturing contain iron, which resulted in a brittle end-product
more modern casting uses stronger alloys that can produce precise parts, reducing the amount of further processing needed
die casting allows for a relatively quick and cheap way to manufacture parts using zinc alloys; however, these are much less precise, more prone to deformities and quick wear, and have poor strength
high-strength polymer plastics are now also being used for handgun frames, where plastic was generally only used for nonstressed parts in the recent past
FORGING & STAMPING
hand forging of iron or steel barrels was a common processes for manufacturing muskets, rifles, and handguns a long time ago
machine forging is now a fairly common process for gun manufacture due to its major benefit of increased strength and durability of iron alloys during the forging process compared to completely melting and casting it
stamping uses large sheets of flat metal to form the thinner parts of a firearm, and is common in military, law enforcement, and commercial firearms
MACHINING
drilling techniques for handguns and rifles form the foundation for the unique characteristics of each gun barrel that makes firearms identification possible
firearms parts that require a rounded surface require turning; the most common component that is turned is the barrel, where random marks produced in the bolt face transfer to the fired cartridge case and appear as breechblock marks
grinding is used to produce crude or refined surfaces on the firearm
milling can produce identifiable marks on breech faces, extractors, ejectors, ejection ports, noncircular firing pins, and cartridge guides that can transfer to the cartridge case
broaching creates spiraled grooves during the rifling process
hand fitting through the use of filing, stoning, and pressure may be required as a form of fine forming; these processes result in nonreproducible marks and patterns unique to that firearm
HIGH-STRESS LOAD PARTS
frames
receivers
slides
bolts
breechblocks
cylinders
LOW-STRESS LOAD PARTS
lock parts
repeating mechanism components
detachable magazines
pins, screws, springs
COSMETIC FINISHING
bluing used on steel parts provides a protective coating approximately two millionths of an inch thick through oxidative means
a protective coating can be applied to chrome or nickel through the process of electroplating
aluminum and titanium get protective coatings through the process of anodizing, which can produce a number of different colors
ASSEMBLY
subassembly is required for parts like hammers, triggers, cylinders, bolts, and slides
final assembly is completed through a combination of hand fitting and drop-in fitting then checked for proper fit through gauges or physical feel