Your analysis is right, and so's your sentence. Percussum isn't really that odd, though there's no real need for it. It's the ordinary Latin way of saying H. hit C. with a club and killed him. Latin makes much use of perf. pass. participles -- it has to, since that's about the only participle it has! (Pres. and fut. actives used much less often.) In Greek you'd use an active aorist (past) participle, H. having hit C. with a club killed him, but poor impoverished Latin can't do that.