SB 742-1
j. This label which reads "Warning: Remove container
a. All models which have a safe setting, except for Fuze, extension and reduce propellant to not more than 25 and
increments before firing in 4.2 inch mortar M2" is applicable
MT, M565. Fuze, MT, M565 not set on safe is a major defect
only to the M2 mortar. The M2 mortar was classified obsolete
b. All models with fuzes requiring a safety wire or pin.
on 13 June 1957, and there are no known weapons in any U.S.
inventory. Some allied countries may still be using the M2
c. M328 series with tetrytol bursters (see para K-2).
mortar; therefore, whenever lots are encountered with missing
d. Red face must not be visible.
labels, a remark should be included on the DSR card to ensure
the lot is not shipped FMS or Grant Aid.
e. Propellant broken below the seam, or total loss of 1/8 to
increment, will be classified a major defect. Propellant
k. Obturator.
broken, but not below the seam, or total loss less than 1/8
(1) The obturator bristles must slant clockwise when
increment, will be classified an incidental defect.
viewed from the rear of the cartridge.
f. When a component is damaged to the extent that its
(2) The bristle strips must be fully seated in the
functional effectiveness has been destroyed, it will be classified
obturator groove with no obvious bulging of the bristle strips
as a defect.
above the obturator groove.
g. Normally done only during initial receipt inspection.
(3) Two slits and white dots on the obturator must be
Assure that gage flange makes even contact with forward edge
of projectile when fully inserted. If possible, establish cause oriented towards the rear of the round, the trailing edge of the
for projectile's failure to gage (such as cocked liner, fuze well obturator must be thinner than the leading edge when
liner not fully inserted, foreign matter in threads, damaged assembled to the cartridge.
threads, etc.).
(4) Other obturator damage (including the bristle
h. Does not apply to new type plug (polyethylene) which strips) which would adversely affect the round's fit in the
mortar tube or result in obturator failure will be cause for
does not require a spacer.
cartridge rejection.
i. Caked explosive in the threads will be classified as a
defect. Explosive dust will not be considered a defect.
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