A pneumatic impact device and method provide a high powered striking force against a target object. The device includes a core shell that houses a piston sub-assembly and a sear arm sub-assembly, and that further defines a forward gas chamber and a rearward gas chamber. The rearward gas chamber is loaded with compressed fluid via a handle actuator. A mostly external sear trigger assembly responds to the impact of a striker plate against the target object, thereby releasing a sear arm that then releases a piston, which is then accelerated forward by the compressed fluid charge. The device can be re-set manually via compressed fluid (e.g., air) in one embodiment, or automatically via a spring mechanism in another embodiment.