Sentence:  The tin cylinder, filled with iron balls, which is fired from our smooth-bored guns, was unsuitable for a rifled gun, because the breaking up of such a projectile in the bore was likely to injure the rifling. Then again, lead balls could not well be substituted for iron ones on account of their liability to <WSD>conglomerate</WSD> or adhere together in lumps. 
Meaning of the word marked with <WSD> tags:  To combine together into a larger mass.