The term 'magnum chaser' is a slang term used to describe someone who is an avid collector of large-caliber firearms, such as magnum revolvers and rifles. The crossword solution for this term is 'opus, ' which is Latin for 'work' or 'TASK.' This term is often used to refer to a creative work, such as a book, painting, or musical composition. In the context of a magnum chaser, it could be interpreted as referring to the TASK of collecting large-caliber firearms.