Browning machine gun caliber .50, M2, aircraft, fixed and flexible. Page: 49
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TM 9-225
BROWNING MACHINE GUN, CALIBER .50, M2 35
seconds' delay occur and the bolt be opened before the powder burns,
injury to the firer or damage to the weapon, or both, may result.
c. Pierced primer.-Perforation of the primer cup by the firing pin
may be caused by an imperfect firing pin or very thin metal in the
base of the primer cup. There are various degrees of this perfora-
tion. A very small perforation will show the escape of gas by means
of a discoloration around the indent made by the firing pin. The
disk from a large perforation may be blown into the action of the
gun with such an escape of gas as to lower the velocity of the bullet.
d. Primer leak.-Gas generated by the explosion of the powder dis-
charge escapes between the walls of the primer cap and the primer
pocket, causing discoloration around the primer and the head of the
cartridge case. The discoloration may be slight, indicating a small
primer leak, or heavy, indicating a large primer leak.
e. Blown primer.-On firing the cartridge, the primer is blown com-
pletely from the pocket of the cartridge case. Although this is a
serious defect, it is seldom encountered.
f. Primer setback.-Pressure developed by the explosion of the
repellent charge forces the primer back against the face of the bolt.
On examination, it will be seen that the primer protrudes above the
head of the cartridge case. The setback of the primer may be slight
or heavy and is due to a defective bolt or cartridge.
g. Leak back of case.-Escape of gas into the action of the weapon
causes this leak. Discoloration due to this escape of gas is along the
body of the cartridge case.
h. Failure of case to ewtract.-This may be due to a poorly formed
or weak extractor, or a defective cartridge.
i. Blowback.-An escape of gas under pressure to the rear is com-
monly referred to as a blowback. Pierced primer, primer leak, blown
primer, primer setback, and ruptured cartridge are known as blow-
backs.
j. Split neck.--The neck of the cartridge case splits in firing and
is accompanied by an escape of gas. Seasonal cracks are of two
kinds; those which can be observed before firing, and those which are
evident after firing.
k. Split body.-A more or less regular longitudinal split in the
body of the case which allows gas to escape.
1. Stretch.-A continuous ring around the body of a fired cartridge
case which shows that the metal stretched when the cartridge was
fired and that with slightly more stretching a complete or partial
rupture would probably result. This is almost always due to im-
proper head space.49
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United States. War Department. Browning machine gun caliber .50, M2, aircraft, fixed and flexible., book, April 30, 1942; Washington D.C.. (https://digital.library.unt.edu/ark:/67531/metadc29988/m1/51/: accessed May 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.