Sentence:  In length, this gun was the same as the French, but weighed 9 cwt. less. It was rifled in six grooves on the <WSD>shunt</WSD> plan, in the form in which it has been generally applied to large guns, with the difference that some of the angles of the grooving were rounded off. ... To impede fouling, a slightly greater windage was allowed in the chamber of the <WSD>shunt</WSD> gun, the diameter there being 0.04 greater than at the mouth of the bore. 
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.