Just my 2 cents: While the technology certainly existed, Han army never used stone-thrower as siege weapon until Three Kingdoms period, AFAIK. However two other siege weapons can be found on Han period arsenal records: The lián nǔ chē (连弩车)and wǔ gāng qiáng nǔ chē (武刚强弩车, shortened to wǔ gāng chē 武刚车). The lián nǔ chē is (believed to be) an up-scaled version of the repeating crossbow. The wǔ gāng qiáng nǔ chē is a horse-drawn wagon armed with heavy crossbow. Usually formed into a Laager (Wagon fort). Battering ram or chōng chē(冲车)are recorded as well. Oh, and that gigantic siege tower lǚ gōng chē (吕公车)seems to be a much later design (Song dynasty and later).