MIL-PRF-71168A(AR)
be white in color. The manufacturer's initial or registered
trade mark (upper case), last two digits of the year of
manufacture and a lower case "S" shall be legibly stamped on the
cartridge head surface. Stamping shall not encroach the primer
pocket or head bevel.
3.4.4 Primer sensitivity. The average height (h) and
standard deviation (s) of the height of fire shall be such that h
+ 3(s) ≤ 33 cm and h - 3(s) ≥ 6 cm.
3.5 Operating requirements. Each cartridge shall provide
the following functional, operational, and performance
capabilities when fired from an unmodified standard issue M60 and
M240B machine gun without any ancillary devices, sighting systems
or modifications.
3.5.1 Chamber pressure. The mean chamber pressure of
cartridges conditioned for not less than 2 hours at 21°C ± 1°C
and fired at that temperature shall not exceed 365 MPa nor shall
the 3-Sigma Standard Deviation of the ambient rounds exceed 400
MPa. No individual chamber pressure shall exceed 400 MPa at any
temperature from -20°C ± 1°C to 40°C ± 1°C.
3.5.1.1 Chamber pressure at extreme temperatures. The mean
chamber pressure of cartridges conditioned for 6 to 12 hours at
-20°C ± 1°C and 40°C ± 1°C and fired at those temperatures, shall
not increase more than 50 MPa above the mean chamber pressure
obtained at 21°C ± 1°C.
3.5.2 Velocity. The mean velocity of cartridges
conditioned for 6 to 12 hours at 21°C ± 1°C, fired at that
temperature and measured at 23.77 meters from the muzzle of the
weapon shall not vary by more than ± 6 percent from the design
velocity. The design velocity is the mean velocity (uncorrected)
obtained during design verification at 21°C ± 1°C.
3.5.2.1 Velocity at extreme temperature. The mean velocity
of cartridges conditioned at -20°C ± 1°C and 40°C ± 1°C for 6 to
12 hours and fired at those temperatures shall not vary by more
than ± 10 percent from the mean velocity at 21°C ± 1°C.
3.5.3 Action time. The action time (overall primer
ignition, propellant burning, plus the time taken for the bullet
to exit the barrel) of cartridges conditioned for 6 to 12 hours
at 21°C ± 1°C, -20°C ± 1°C and 40°C ± 1°C and fired at those
temperatures shall not exceed 4 ms.
3.5.4 Dispersion. The average mean radius of the impact of
10 rounds at a distance of 100 meters shall not exceed 78mm.
3.5.5
Cyclic rate.
The cartridges shall function the in
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