FAILURES AT PRACTICE WITH T. & P. FUZE MARK IV. 541 
(a) The head may set back and break the central tube, or 
the head may be broken off on impact. 
(b) If the disc supporting the bullets is weak the weight of 
the bullets setting back on to it may cause it to buckle 
down and tear away the central tube from the fuse 
socket. 
In either case the continuity of the passage for the flash of the fuze 
is broken, and it can not reach the bursting charge in the base of the 
shell. 
5 and 6.—If the spindle, and with it the head, of the fuze is broken 
off or distorted on impact so that the fire hole in the seating of the 
time ring is practically left uncovered, a portion of the flash passes 
upwards and the remainder may not have sufficient strength to ignite 
the bursting charge. 
9. —In soft ground the shell may penetrate so far that the burst 
cannot be seen, the fuze will not be extinguished as the composition 
contains its own supply of oxygen and does not require a supply of 
external air for burning. 
10. —The percussion arrangement can not be relied on to act at 
angles of incidence less than 2°, that is at ranges less than about 1,000 
yards in the 12-pr. 6 cwt., and 1,150 yards in the 15-pr. 
12. —In addition to the results explained under (3) bad clamping 
has a tendency to cause short bursts, because if the time ring and 
leather washer are not well pressed down on to their seating on the 
fuze body the flame has a tendency to jump across from one portion of 
the composition to another and cause it to burn short. 
13. —In this case the fuze might be fired set at 2, or on the short 
portion of the time ring. 
14. — In fuzes previous to 152 thousand it was found that the time 
safety pin sometimes sheared when firing percussion shell, the pin has 
been strengthened and the fuze is now free from this defect. 
15. -—A burst in the gun may be caused by a rebound of the needle 
pellet, this could only happen if the centrifugal bolt had not engaged 
in the slot in the body or had been left out. 
A short burst may be caused by 
(a) The needle pellet creeping; this is almost impossible in 
the Mark IV., as a feather in the body engages in a slot 
in the pellet and compels them to move together more¬ 
over the spring checks any tendency to this. 
(b) A defective washer under the composition ring or de¬ 
fective seating under the washer may allow the flame 
of the composition to jump as explained under (12). 
16. —A weak shell may break up in the bore, this is most improbable 
with a forged steel shell; or if the steel disc supporting the bullets is 
too weak to sustain the shook of discharge, the whole mass of the 
