There was a series of Japanese films made in the 70's which are considered as nothing less than "sado-porn" by the few who have actually managed to see them, in which the extent of the depiction of violence and brutality was taken to unbearably brutal extremes as opposed to physical, special-effects reliant gore. I don't really know anything about them but I know one of the offerings was the cheerfully titled Oxen-Split Torture, which kind of speaks for itself.
There was also a video-short shot in the late 70s known simply as The Castration Movie, made by associates of the underground avant-garde 'Psychic TV' troupe. Proliferated in hushed circles throughout the years, it's very realistic and convincingly rudimentary and austere, and has only really been debunked as not being a genuine 'snuff' movie since the Internet came along.