A biopsy device comprises a needle, a body portion, and a needle firing assembly. The needle firing assembly is operable to fire the needle distally relative to the body portion. The needle firing assembly includes two translating members, a resilient member, and a motor. The motor is operable to selectively move the first translating member distally and proximally. The second translating member is secured relative to the needle such that the needle and the second translating member translate unitarily. The resilient member compresses as the first translating member is moved distally toward the second translating member. The first translating member is then secured to the second translating and the translating members are moved proximally while holding the resilient member in the compressed state. The second translating member is released from the first translating member when they reach a proximal position, which allows the resilient member to fire the needle distally.