Page 138 - FAT 105 4.17 MOODLE
P. 138
its concentricity is key. When the bullet Because the barrel is an extremely criti-
leaves the muzzle, the high pressure gas- cal component, it is always made of steel,
ses pushing against it will still act upon stainless steel, or some other steel alloy.
it in the open atmosphere. If the muzzle Only steel (and its alloys) can be trusted
shape is damaged or not concentric, it will to withstand the forces experienced when
direct the gas unevenly around the bul- a cartridge is discharged. The heat treat-
let, forcing it off of its intended course. A ment of the barrel is also critical to its
concentric muzzle will distribute the exit- performance. The barrel must exhibit a
ing gasses evenly around the bullet, caus- certain amount of “flex” or elastic defor-
ing little to no disruption in trajectory. mation in order to contain the huge pres-
sures inside. A barrel that is too hard may
There are different shapes of muzzle crown
be brittle and crack or break instead of
each with their own benefits, though the
flex under pressure.
concentricity of the crown is more impor-
tant. The most popular muzzle shapes are There are basically three manufacturing
flat, round, and 11°. A flat crown is exactly processes used to complete firearm bar-
what its name implies: flat. The flat crown rels and form rifling. All three processes
is perfectly 90° perpendicular to the bore, begin in the same manner, as a solid rod
with a slight 45° bevel at the bore. The blank. The blank is then drilled under-
round crown is also appropriately named sized (smaller than the final dimensions),
because the muzzle shape is rounded. The lapped, and polished. This is where the
11° or “target” crown has gained a lot of three processes differ. The three basic
popularity as a precision muzzle crown. rifling forming processes are hammer
The 11° crown consists of an 11° bevel, forged, button, and cut. The three process
perpendicular from the bore. This slight can be used to form both traditional ri-
bevel is believed to be the best shape for fling as well as polygonal rifling with
the smoothest transition of the exiting varying numbers of lands and grooves (3,
gasses. This ensures the exiting gasses do 4, 5, 6 lands).
not disrupt the bullet’s intended trajectory.
Figure 12: Various firearm barrels.
134
