Sentence:  "The <WSD>shunt</WSD> system", of which the 64-pr. is the only example now in the service, has been considered inferior to the Woolwich, because besides being unnecessarily complicated, the grooves which are cut with abrupt sharp angles weaken the gun. ... [I]n the <WSD>shunt</WSD> gun, however, in addition to the mere fact of the driving side of the double groove being shallow, and the loading side deep, the two grooves join in one deep one at 2 feet 7.5 inches from the muzzle, ... 
Meaning of the word marked with <WSD> tags:  The shifting of the studs on a projectile from the deep to the shallow sides of the grooves in its discharge from a shunt gun.