c. Misfires with Shock Tube.
(b) Obtain new like component and spool back
to initiating point.
(1) The most common cause of a misfire in a
(c) Install new igniter and attempt to fire (range
shock tube priming system is the initiating element, usu-
clearance received, etc.)
ally an M81 igniter. The most common failures with this
item are incorrect placement and securing of shock tube
within the M81, and poor cut of shock tube.
After the charge has been fired, deal with
(2) If two or three retries with the M81 do not re-
the unfired relay cap and its attached (par-
sult in firing, cut the shock tube, replace the igniter with
tially fired) shock tube in accordance with
a new one and repeat firing procedure assuring the shock
standard procedures for disposing of an un-
tube is properly attached to M81 with a clean cut.
fired blasting cap.
(3) Another misfire mode with the M81 is that the
primer fires, but blows the shock tube out of its securing
mechanism without firing it. (This would usually be due
(7) If the first component of the firing train was
to the shock tube not having been properly inserted and
not the one which failed, check out each low strength cap
secured in the igniter). The corrective action is to cut ap-
(M12, M13) until fault is found. Refer to (6) to replace
proximately 3 feet from the end of the shock tube, re-
low strength component, spool back. If all low-strength
place the igniter, and repeat firing procedure.
components have fired, see FM 5-250 for placing supple-
(4) If the igniter appears to have functioned prop-
erly (primer pops and smokes) but the charge did not
(8) If the failed component appears to be the final
fire, cut one-foot section from the shock tube starting ap-
high strength blasting cap, it may be replaced as above if
proximately six inches from the igniter. Hold the one-
it is above ground and easily accessible. If the failed high
foot piece of shock tube so that one end is over the palm
strength cap is below ground, basic clearing procedures
of the hand and gently blow through the other end. If a
of 6 (b) above apply. If it is placed in a plastic explosive
fine powder is blown from the shock tube, it has not
charge, it must not be disturbed.
fired. If this is the case, install a new igniter on the fresh-
ly cut end of the priming shock tube.
(9) The brightly colored tags attached to the shock
tubes of M11, M15 and M16 caps are there to help locate
(5) If the igniter/initiating element functioned
the caps and to avoid digging too close to them.
properly and if no fine powder was blown from the shock
tube in the previous step, or the shock tube was heard to
fire or its flash was seen, observe the standard half hour
waiting time before going down range to check the next
element(s) in the priming train.
The red tag is one meter from the detonator
(M11, M15 and M16) and the yellow tag is
two meters from the detonator. They pro-
vide a visual indicator to determine if caps
have functioned with the unfired relay cap
NEVER YANK OR PULL HARD ON
and its attached (partially fired) shock tube
THE SHOCK TUBE BECAUSE IT
in accordance with standard procedures for
MAY ACTUATE THE DETONATOR.
disposing of an unfired blasting cap.
(6) After the waiting time has passed, proceed
down range and check the detonator of the first compo-
nent in the priming train. If the detonator has not fired:
(a) Cut one foot forward of detonator.