4 . 4 . 4 . 2 A m m u n i t i o n . T h e M60 high pressure test cartridge shall
b e used for the high pressure resistance test, selected lots of M80
ball cartridge which gave an average mean radius of 4 inches or less
in 600) yard ammunition acceptance tests shall be used in the targeting
a n d accuracy tests and unselected lots of M80 ball cartridge shall be
u s e d in the functioning and reliability tests (see 6.1).
4 . 5 Test methods.
4 , 5 . 1 Tightness of draw test. The barrel and receiver assemblies
s h a l l be tested for tightness of draw requirements (see 3.3.18) using
the inspection equipment in accordance with Drawing F7271792. The
b a r r e l and receiver holdting fixture shall be secured to a bench or other
s u i t a b l e s u r f a c e . The barrel and receiver assembly shall then be secured
i n the fixture as specified on the applicable drawing and the torque
a p p l i e d to the receiver in the direction to disassemble it from the
4 . 5 . 2 Headspace test. Rifles shall be examined for headspace
r e q u i r e m e n t (see 3.3.19) a f t e r p r o o f f i r i n g , p r i o r t o a c c e p t a n c e} u s i n g
the inspection equipment in accordance with Drawing F7274733. The
r i f l e shall be held in a horizontal position with the bolt open. The
s p r i n g loaded plug shall then be inserted in the barrel chamber and the
b o l t manually returned to the fully locked position, The indicator portion
o f the gage shall be set to zero using the setting check as specified on
t h e applicable drawing and then inserted in the barrel from the muzzle
e n d until it contacts the spring loaded plug. T h e indicator shall then
b e read to determine if the headspace is within the specified requirements.
4 . 5 . 2 . 1 In the event of a dispute over the test results when tested
a s specified in 4.5.2, the referee test method shall be as specified in
4 . 5 . 2 except that rifles shall be examined with the operating rod dis-
c o n n e c t e d from the bolt.
4.5.3 Firing pin indent test. Rifles shall be tested for firing
p i n indent requirement (see 3.3.26 ) using the inspection equipment in
accordance with Drawings D7271741 and C7318984. The rifle shall be held
i n a horizontal position with the bolt held open and the copper compres-
s i o n cylinder holding fixture containing the copper compression cylinder
s h a l l be inserted in the barrel chamher. T h e bolt shall be manually
r e t u r n e d to battery position and the trigger pulled to release the hammer
a n d indent the copper cylinders T h e holding fixture shall be removed
f r o m the rifle and the depth of the indent in the copper cylinder computed
b y measuring the distance from the original surface of the copper cylinder
( b e f o r e indentation) to the bottom of the firing pin impression. The
i n d e n t shall be visually examined to determine of the concentricity re-
quirement has been met.